DIY abs fault diagnosis

DIY ABS diagnostics

A car's Anti-lock Braking System is a system that regulates the brake fluid pressure in the brake circuits, which helps prevent the wheels from locking during braking. In other words, this system prevents skidding, which provides the following benefits:

Increasing vehicle stability.
Reducing braking distance.
Saving rubber and preserving the studs on car tires.

In addition to its primary function, anti-lock braking system sensors and valves are used for many other vehicle systems. For example, exchange rate stability system or emergency braking assistance system.

The stability control system brakes certain wheels during sharp turns or drifts, which significantly improves safety performance.

Brake Assist keeps the brake pedal depressed until the vehicle comes to a complete stop.

How the anti-lock braking system works

How to diagnose ABS yourself? — to answer this question with confidence, it is important to know the structure of the system itself. To do this, let’s look at several individual parts of it:

Speed sensors. Sensors are located near each wheel of the car. They transmit information about the rotation speed of each wheel to the ABS control unit.
ABS control unit. The control unit receives signals from speed sensors, analyzes the situation, and, in the event of a wheel lock, transmits a command to the hydraulic control unit.
The hydraulic control unit, having received a signal about a blocked wheel, closes the brake fluid channel going to this wheel.

The result is that as soon as the wheel is locked, the system “releases” it. Once this happens, it is blocked again. All this happens with high frequency, and as a result, the wheels rotate at maximum effort, but without switching to skidding.

DIY ABS diagnostics

The very first sign of a malfunctioning ABS system is a light on the dashboard. After it lights up, it is important to immediately make a diagnosis. Let's consider the actions that need to be taken if the ABS malfunctions:

Check the fuses and relays of the anti-lock braking system control unit.
Compare the tire pressure - it should be the same everywhere.
Examine the rotor of each sensor for contamination.
Use a tester to measure the resistance in each of the sensors with the ignition on. Lift the wheel on a jack and rotate it and observe the changes.
Check the integrity of the wires coming from the sensors to the control unit.
Check the integrity of the wires going to the ABS hydraulic unit.

The best diagnostic option would be to check by connecting a laptop or smartphone to the diagnostic connector - this will save a lot of time and instantly determine the cause of the breakdown.

ABS Lada Vesta error codes and their interpretation

Diagnosing ABS yourself is a rather difficult task if you do not have diagnostic equipment (cable, laptop, and software). If you have the ability to read errors, then by comparing their codes with the description, you can much faster determine the cause of the malfunction. The following are the errors that “light up” the anti-lock braking system malfunction light:

U0121 - no data from the ABS system controller
U0122 - no data from ESP system controller
U0415 - incorrect data from the ABS system controller
U0416 - Invalid data from the ESP system controller

In most cases, the absence of data from the controller indicates a malfunction. If the diagnostics indicate errors U0415 or U0416, then there is a high probability of sensor malfunction or damaged wires. Also, do not forget that with different tire pressures, the control system may receive incorrect data from the controller and indicate the last two errors.

Anti-lock braking system and safety

Many people mistakenly believe that ABS does not bring any benefit and is even an obstacle to safe driving. This is a rather deep-rooted opinion, and to the question “how do you justify this?” very often you can hear something like “on loose snow, ABS increases the braking distance.” In fact, the length of the braking distance is not particularly different.

But the main goal of this system is not to shorten the braking distance, but to increase traction during braking. It is impossible to brake by skidding and at the same time go around an obstacle - the wheels will not obey you.

But if your car is equipped with an ABS system, then you don’t have to worry - feel free to press the brake pedal all the way and continue to maneuver.

It is important to understand that your mind adapts to this system, and it is very difficult to get used to the ABS not working. It is for this reason that it is necessary to immediately diagnose and repair the anti-lock braking system at the first sign of a malfunction.

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Source: https://olade.ru/diagnostika-ABS-svoimi-rukami

Checking the ABS system yourself: how to find the problem and fix it?

An anti-lock brake system is an essential component of any modern car. Not all domestic drivers are accustomed to this technical equipment. But some have already learned not only to take advantage of its benefits, but also to independently diagnose the operation of the system.

The essence of ABC is that during emergency braking, the movement of all four wheels is prevented from blocking. This works to increase vehicle stability and reduce braking distance. It is especially important when driving on slippery surfaces - gravel, icy, wet asphalt. The car does not skid, the level of controllability remains high, although the brake pedal is pressed to the limit.

ABS is a complex complex that is connected to the braking system.

Key parts are a hydraulic unit that modulates fluid pressure, wheel speed sensors, their location, and a computer that processes information from the sensors and transmits it to the main unit. Location: under the hood, in the space between the brake cylinders.

Method of operation of the anti-lock brake system

A strong press on the brakes is detected by sensors, and the system deciphers this as the car skidding. There is a signal about the need to reduce the braking force.

The pressure of the special fluid in the brake line decreases, and the wheels are unlocked. Didn't succeed the first time? The system will continue to try until the brake pad tension is relieved.

The operation of ABS is schematically: braking - analysis - disinhibition process.

The system's response speed is very high. It starts working even before the wheel locks. The driver sees a corresponding signal on the control panel and feels characteristic shocks in the pedal. If the warning message does not disappear from the screen, this indicates a problem.

You should not rely entirely on the system. It creates a false illusion of driving safety for the driver. It is not always possible to shorten the braking distance of ABS, especially when it comes to cornering. In addition, the system is difficult to predict. A motorist is rarely able to determine where his braking distance ends.

Should I be afraid of ABS malfunctions? This system does not need repair often, as it is equipped with fuses and special relays. Failure means that the brakes now work without additional control, but this does not directly affect their functionality.

So you can drive a car with a problematic anti-lock braking system, but it’s better not to. Many drivers ignore the danger and overestimate their level of control over the vehicle. Even the most experienced motorist can make mistakes when braking in an emergency.

So as soon as the first signs of a malfunction appear, repair it.

How to understand that the ABS is broken

In the simplest cases, the problem will be indicated by an indicator on the control panel. A sensor that lights up for 10 seconds turns on while driving and indicates a malfunction. In most cases, problems can only be identified while driving.

Individual failures are evident at a certain speed - 25 km/h.

Before a thorough search, you need to exclude two points:

recent tire change. Studded tires on the drive wheels increase the diameter, causing the rear and front elements to rotate at different speeds, which causes the malfunction sensor to light up;
The abs sensor can also trigger slippage.

False signals have been eliminated, let's move on to serious malfunctions.

Causes and symptoms of ABS problems

The sensor wire broke and the controller unit broke. Signals about angular velocities are not transmitted, the error signal lights up, and the system turns off.
Wheel sensors are faulty. The system turned on, performed self-diagnosis, found an error, and continued working. The contacts have oxidized, the connection to the system power supply is broken. Another option is that the wheel sensors have shorted to ground.
Tires have different pressures, different tread patterns, and different degrees of rubber wear. One of the wheels goes slower than the others. Indications of angular velocity are transmitted by an additional device.
Mechanical damage to parts: separators and grilles may break, the hub bearing may wear out, play may appear, the wheel sensor rotor may break, and the operation of the pump may be disrupted.

Mechanical causes of the malfunction prevent the ABS from even starting.

Most of the above problems can be solved on your own. After all, complete replacement of equipment is very expensive. As the experience of auto mechanics shows, wheel sensors break more often than other parts. They are located next to the hubs and take on all the dirt. By examining them, you can begin the diagnosis.

The most unpleasant thing that can happen is that the control unit turns out to be faulty. And it is very expensive. But the complex works with a protective relay and rarely creates problems for the motorist. Therefore, you can check the block last. The procedure begins with the front wheels:

remove the sensor, clean with kerosene, white spirit;
checking the ABS sensor involves a thorough inspection of the wheel hub teeth. The revolutions are read from them. Dirty, clogged teeth – incorrect information and system freeze;
remove and clean the reverse gear sensor;
how to check if the electrical resistance is correct? Compare with the readings from the car's factory manual:
lift the body with a jack, spin the wheel, and while rotating, measure what voltage passes through the sensor winding. Compare with indicators from the directory;
check the bearings. A worn hub is one of the most common causes of problems. After cleaning with kerosene and checking by shaking, the faults will become obvious. Replace parts if necessary. Use a multimeter to check the operation of the sensor.

Did the procedure fail? The next step is checking the protective relay. Its location is indicated on the car wiring diagram. The device has aluminum walls and a plastic cover. There are a couple of fuses inside and it is quite possible that one of them simply burned out. When buying a car on the secondary market, you need to inquire about the location of the protective relay from the previous owner.

Are the fuses ok but the system is still faulty? Let's diagnose the relay itself:

disconnect the electrical connector;
connect the voltmeter probes to the first two numbered block pins;
turn on the ignition, measure the network voltage - 20V. There is no voltage - check the negative connector to see if the connection has gone to ground of the car;
remove the relay, connect to the battery (terminals number 5 and 6). Give 12 V. Clicks are heard - the device is working, if not - it needs to be replaced.

Checking the abs sensor

The first thing is to remove the dirt. The next step is to measure the voltage in the node. The norm is 800-1200 Ohms, but there are nuances, it is better to check the factory data in the manual. The network grows endlessly - a sign of a break. Resistance is zero - there is a short circuit in the circuit.

https://www.youtube.com/watch?v=8wGuwnuPS9Q

All wiring must be tested. Here are the indicators that are considered acceptable: insulation - 20 kOhm or more, legs - from 6 to 25 Ohm.

Sensor problem? It needs to be replaced with a new one. If the entire system is examined, but a fault is not found, then the problem is in the control unit. You should not deal with it yourself - you will have to have it checked at a service station and repaired by qualified technicians.

Source: http://cars-bazar.ru/remont/proverka-datchika-abs

How to check the ABS sensor with a tester or multimeter, find out its performance using an oscilloscope, test diagram + video and other nuances of the issue

ABS sensors play an important role in the operation of the car's braking system - the braking efficiency and uninterrupted operation of the unit as a whole depend on them. The sensor elements send data about the degree of rotation of the wheels to the control unit, and it analyzes the incoming information, building the desired algorithm of actions. But what to do if you have doubts about the serviceability of the devices?

Symptoms of a device malfunction

The fact that the ABS sensor is faulty will be indicated by an indicator on the instrument panel - it lights up when the system is deactivated, which turns off even if there is the slightest problem.

Evidence that ABS has ceased to “interfere” with the operation of the brakes:

Wheels constantly lock during heavy braking.
There is no characteristic knocking noise with simultaneous vibration when pressing the brake pedal.
The speedometer needle is delayed relative to acceleration or does not move from its original position at all.
If two (or more) sensors on the dashboard are faulty, the parking brake indicator also lights up and does not go out.

The ABS indicator on the dashboard indicates a system malfunction

What to do if the ABS warning lamp on the car’s dashboard does not behave quite correctly? You should not immediately change the sensor; first, the devices should be checked - this procedure can be performed independently, without resorting to the services of highly paid craftsmen.

Ways to check functionality

To determine the condition of a part, we will perform a series of steps to diagnose it, moving from simple to complex:

Let's check the fuses by opening the unit (inside the passenger compartment or in the engine compartment) and inspecting the corresponding elements (indicated in the repair/operation instructions). If a burnt component is found, we will replace it with a new one.
Let's inspect and check:
- integrity of connectors;
- wiring for abrasions that increase the risk of a short circuit;
- contamination of the part, possible external mechanical damage;
- fixation and connection to ground of the sensor itself.

If the listed measures do not help to identify a device malfunction, it will have to be checked using instruments - a tester (multimeter) or an oscilloscope.

Tester (multimeter)

This method of diagnosing the sensor will require a tester (multimeter), instructions for operating and repairing the car, as well as PIN - wiring with special connectors.

The device combines the functions of an ohmmeter, ammeter and voltmeter

To obtain complete information about the performance of the ABS sensor, you need to measure the resistance in the device circuit:

We lift the car with a jack or hang it on a lift.
Remove the wheel if it prevents access to the device.
Remove the cover of the system control unit and disconnect the controller connectors.
We connect the PIN to the multimeter and the contact socket of the sensor (the connectors for the rear wheel sensors are located inside the cabin, under the seats).
We connect the PIN to the tester and the contact socket of the sensor
We measure the resistance (tester in ohmmeter mode) at the contacts of the device. We compare the readings of the device with the car’s operating manual, where the required parameters should be indicated.
We check the electrical circuit by ringing the sensor wiring for a possible short circuit.
We spin the wheel manually and at the same time measure the resistance - the tester readings should change depending on the rotation speed.
We switch the tester to the “voltmeter” mode and measure the voltage on the sensor - we turn the wheel at a frequency of 1 rev/sec, monitoring the readings of the device. Voltage parameters from 0.25 to 1.2 V are considered optimal, but it should be taken into account that increasing the wheel speed necessarily increases them.

The device readings must correspond to the data specified in the repair and operation manual for a particular vehicle. If the device resistance:

below the minimum threshold - the sensor is faulty;
approaches zero - short circuit;
unstable (jumping) at the moment of twitching of the wire - a violation of contact inside the wiring;
infinity or no readings - wire break.

Video “Diagnostics of the ABS sensor”

How to check using an oscilloscope (with connection diagram)

In addition to self-diagnosis of the sensor with a tester (multimeter), it can be checked using a more complex device - an oscilloscope.

The device examines the amplitude and time parameters of the sensor signal

To diagnose the ABS sensor with an oscilloscope, you must:

Fully charge the battery so that during the measurement you can observe voltage drops (jumps) on the connectors or conductors.
Find the touch sensor and disconnect the upper connector of the part.
Connect an oscilloscope to the contact socket.
Connecting the device to the ABS sensor connector (1 - toothed disc-rotor; 2 - sensor)
Rotate the suspended wheel (by lifting the car on a jack or lift) at a constant frequency of 2-3 revolutions per second.
Detect the amplitude of signal oscillations on the device display.
Rotate the second wheel of the axle and similarly detect vibrations.

The serviceability of the ABS sensor is indicated by:

equal amplitude of signal fluctuations when the wheels of one axle rotate;
absence of amplitude beats when diagnosing with a sinusoid signal of lower frequency;
maintaining a stable, even amplitude of signal fluctuations not exceeding 0.5 V when the wheel rotates at a frequency of 2 rps.

Note that an oscilloscope is a rather complex and expensive device. Modern computer technologies make it possible to replace this device with a special program downloaded from the Internet and installed on a regular laptop.

Video “Laptop instead of an oscilloscope”

Checking a part without instruments

The easiest way to diagnose a device without instruments is to check the magnetic valve on the induction sensor. Any metal product (screwdriver, wrench) is applied to the part inside which the magnet is installed. If the sensor does not attract it, it is faulty.

What to do if a breakdown is detected

What to do with the ABS sensor if a malfunction is detected? If the problem point is the device itself, it will have to be replaced, but in the case of electrical wiring, you can fix the defect yourself. To restore its integrity, we use the “soldering” method, carefully wrapping the joints with insulating tape.

If the ABS indicator on the dashboard lights up, this is a clear sign of a sensor failure.

The described steps will help identify the cause of the breakdown, but if you lack knowledge and experience, it is better to contact a car service center.

Otherwise, illiterate diagnostics of the condition, coupled with improper repair of the device, will reduce the effectiveness of the anti-lock braking system and can provoke an accident.

Source: http://pol-z.ru/sposobyi-proverki-datchika-abs/

Diagnostics and principle of operation of the ABS sensor

With the advent of the new braking system, vehicle safety during emergency braking has increased. The system began to be installed in the 70s. The ABS system includes a control unit, a hydraulic unit, wheel brakes and speed sensors.

The main device of the ABS is the control unit. It is he who receives signals from touch sensors in the form of the number of wheel revolutions and evaluates them. The data obtained is analyzed and the system draws a conclusion about the degree of wheel slip, their deceleration or acceleration. The processed information is sent in the form of signals to the magnetic valves of the hydraulic unit, which performs the control task.

Pressure is supplied from the brake master cylinder (MBC), which ensures the appearance of pressure in the brake caliper cylinders. Thanks to the pressure force, the brake pads are pressed against the brake discs.

Regardless of the situation and the force the driver presses the brake pedal, the pressure in the brake system will be optimal. The advantages of the system are that each wheel is analyzed and the optimal pressure is selected, thereby preventing wheel locking.

Full braking occurs due to the pressure in the brake drive system, regulated by ABS.

This is the principle of ABS operation. On vehicles with rear-wheel drive and all-wheel drive, there is only one touch sensor, which is located on the rear axle differential. Information about the possibility of blocking is taken from the nearest wheel, and the command about the required pressure is transmitted to all wheels.

The device that controls magnetic valves can operate in three modes:

With the inlet valve open and the outlet valve closed, the device does not prevent pressure from increasing.
The inlet valve receives the appropriate signal and remains closed, without changing the pressure.
The exhaust valve receives a signal that the pressure is decreasing and opens, while the inlet valve closes and the pressure decreases as the check valve turns on.

Thanks to these modes, the pressure decreases and increases in a stepwise system. If problems arise, the ABS system is deactivated and the braking system operates without its participation. On the dashboard, the corresponding indicator indicates problems with ABS.

Sensor check

If the abs sensor is faulty, it does not transmit the necessary commands to the system and the automatic braking system ceases to perform its functions: when braking, the wheels lock. If the message on the dashboard lights up and does not go out, then you need to urgently contact service.

The induction type sensor is an induction coil that works in tandem with a toothed metal disk located on the wheel hub. Often the cause of the malfunction is a broken wire. It is this fault that we determine using a tester, a soldering iron and pins for repair.

The pins are connected to the connectors and the tester measures the resistance of the abs sensor, which must be within the limits specified in the operating manual. If the resistance tends to zero, then this indicates the presence of a short circuit. If it tends to infinity, then there is an open circuit.

Then the wheel is checked and the resistance is checked, it must be changed, in this case the sensor is working. If breaks are found during inspection, they must be repaired. Breaks should be connected only by soldering, not twisting, to avoid new breaks, oxidation, etc. Each device has its own marking, wire color and polarity. We must adhere to these data.

If the sensor is broken, you need to figure out how to remove the abs sensor and replace it. When choosing a device, you must first of all focus on quality.

To fully diagnose the sensors, you must not only check the contacts of the device itself with a tester, but you should also ring all its wiring. One of the reasons for incorrect operation is a violation of the integrity of the wiring. If the devices are working properly, then the resistance indicators are as follows:

leg – front right abs sensor (7 - 25 Ohm);
insulation resistance level – over 20 kOhm;
leg – rear right abs sensor (6-24 Ohm).

Many cars have a self-diagnosis system. They display error codes on the information screen, which can be deciphered using the operating instructions.

What kind of malfunctions can there be?

There are four ABS fault conditions:

During the self-test, an error is detected and the ABS is deactivated. The reason may be an error in the controller unit or the presence of breaks in the wiring of the rear right abs sensor, or any other sensor. No angular velocity measurement signals are received.
After switching on, ABS successfully undergoes self-diagnosis and turns off. The reason may be broken wires, oxidation of contacts, poor connection at the contact points, broken power wire, short circuit of the sensor to ground.
After turning on, the ABS undergoes self-diagnosis and detects an error, but continues to work. This can happen if there is a break in one of the sensors.
Information about the angular speed of the wheel comes from an additional device. The cause of this malfunction may be due to different tire pressures and tread patterns. If one tire is flat, or one wheel has a rougher tread than the others, the wheel will slow down. The same effect will occur if the car is equipped with tires with different degrees of wear.
ABS doesn't work. The reason may be a break in the wires, the wire near the sensor may have broken off, the wheel bearings may have worn out, there is play or there may be breaks in the wheel sensor rotor.

To correct problems, you need to check the play, tire pressure, and the condition of the wheel sensor rotor (comb). If the comb is chipped, it must be replaced. Check the condition of devices and wires that connect to them. If these measures do not help, then the problem is in the electronics. In this case, for accurate diagnosis you need to get the code.

Video “Diagnostics of the ABS sensor”

The recording shows how the process of diagnosing the ABS sensor of a BMW car takes place.

Source: http://MineAvto.ru/remont/tormoznaya-sistema/datchik-abs-828.html

DIY ABS diagnostics: faults and their causes

When purchasing an imported car, many cannot get enough of its comfortable operation. Today, a vehicle is comparable to a computer, as it is packed with a variety of electronics designed for comfort and reducing the risk of accidents.

Technical equipment responsible for safety includes such an interesting option as ABS (Antilock Brake System).

Although it has long been established in Russia and has become the standard equipment for all new cars, there are still those who have encountered it for the first time.

The purpose of ABS is to prevent all four wheels from locking during emergency braking.

This allows the vehicle to maintain stability when driving, and on surfaces with a low coefficient of adhesion (gravel, wet asphalt, snow, ice) to shorten the braking distance.

In addition, ABS allows the car to remain controllable even with the brake pedal fully depressed and not skid. This multi-component unit, connected to the brake system, is located under the hood between the master cylinder and the brake caliper cylinders.

The ABS system consists of a main hydraulic unit for modulating fluid pressure, a sensor system that monitors the rotation speed and location of the wheels, as well as a computer in which information from the sensors is processed and sent signals to the main unit.

The ABS sensor system monitors the speed of rotation of the wheels and the vehicle itself.

When you press hard on the brake pedal, the sensors detect that the car is skidding and send a signal to the unit to reduce the braking force, after which the fluid pressure in the brake line drops and the wheels are unlocked.

Moreover, if the brake pads do not release, the process is repeated until it returns to normal. In short, the entire work of ABS comes down to the cycle of braking - analysis - disinhibition.

The system works instantly, even before the wheel locks; a signal about this is sent to the dashboard and characteristic shocks appear in the brake pedal. When the inscription on the instrument panel is permanent, this indicates a malfunction of the ABS.

Remember that no matter how active ABS is in terms of safety, the main thing is still the driver.

The presence of ABS in a car creates the illusion of safety for many, but in practice, even if the system takes control of turns and directional stability, it in no way reduces the braking distance.

With ABS, it is not easy to calculate the braking distance and predict where the vehicle will stop.

Although modern ABS systems have fairly high reliability and can operate for a long time, they, like any other systems, can fail. This happens extremely rarely, because the electronic units are protected by special relays and fuses. If a breakdown does occur, it does not in any way affect the performance of the entire braking system.

The ABS module simply turns off, and the braking system begins to operate normally. You should not ignore the violation, as you may overestimate your capabilities or simply forget yourself during emergency braking. At the first sign of a malfunction, you should not immediately go to a service station; you can try to solve the problem yourself - by diagnosing the ABS.

The first sign of a system failure is an indicator on the dashboard. When the sensor does not go off within 6-10 seconds or turns on while driving, the system is faulty and is not functioning properly.

It is important to know that module failure cannot be detected only when the vehicle is stationary; some failures can only be recognized when driving at speeds of 25 km/h. Before you start looking for problems, remember if you have changed the tires on your wheels.

Since often, in order to save money, many install studded tires in winter only on the drive wheels. And since the diameter increases slightly, the wheels begin to rotate at different speeds, which causes the system to blink.

In addition, there are cases when the sensor lights up during slipping, but, as a rule, in both cases the indicator does not light up for long or flickers from time to time.

There can be quite a lot of problems with the anti-lock braking system; there are 4 common causes of ABS malfunction:

There are breaks in the abs sensor wire or a malfunction of the controller unit. In this case, an error is displayed, signals about changes in angular velocities stop being sent, and the entire system turns off.
Failure of wheel sensors. When the ABS, after switching on, undergoes self-diagnosis and finds an error, but continues to work. The reason is most often oxidation of the contacts, poor connection to the system power supply, or a short circuit of the wheel sensors to ground.
Different tire pressures and tread patterns. As a rule, information about the angular velocity in this case comes from an additional device. When one of the wheels is flat or the tread of one wheel is rougher than the others, it begins to slow down. In addition, the same effect can be observed if you install tires with different degrees of wear.
Mechanical damage to elements - wheel bearing separators, grilles, broken wire near the sensor, wear of the wheel bearing, presence of play and fracture of the wheel sensor rotor. With these breakdowns, the ABS does not start at all. This could also include a failure of the ABS pump.

All of the above problems can be solved on your own; sometimes it is enough to identify the problem and repair some ABS units rather than having to completely replace the expensive equipment.

The most vulnerable in the ABS circuit are the wheel sensors, which are located next to the rotating hubs and axle shafts.

The location of the sensors is poor, since dirt and increased play in the hub bearings can cause a malfunction in their operation, thereby nullifying the entire operation of the anti-lock brake system.

ABS sensor on a car wheel

Often the performance of the unit is affected by the voltage between the battery terminals. If the voltage is reduced to 10.5V or lower, the system itself may abruptly shut down through the safety block.

Since the safety relay always reacts to unacceptable surges and voltage fluctuations in the vehicle network. Such situations can be avoided if you do not disconnect the electrical connectors with the ignition on and the engine running.

You need to constantly monitor the connection contacts on the generator and do not start the engine by “lighting up”.

The most expensive part to replace is the control unit, but as mentioned above, it is protected by a relay, which reduces the risk of its breakdown. The only thing that can disable it is a temperature difference, which we also described above. Therefore, the central part of the system can be safely excluded or moved to the last check point.

Do-it-yourself ABS diagnostics starts with the front wheels:

We remove the sensor.
We clean it from dirt and accumulated deposits with kerosene or white spirit.
We inspect the teeth on the wheel hub. It is from them that the sensor reads high-speed revolutions; when the teeth are clogged with dirt, then the data is read incorrectly, which leads to the ABS freezing.
We remove blockages from them, and we do the same with the reverse gear sensor.
Afterwards, you need to check the electrical resistance, which is specified in the vehicle’s factory manual. When you cannot find out the exact resistance, go to the store and ask the seller about the resistance for your vehicle model.
When everything is in order with the sensors, switch the multimeter to voltmeter mode, which measures alternating voltage.
Raise the car with a jack and spin the wheel, and while rotating it, measure the voltage in the sensor winding. You can also find out the normal unit of voltage from your car's manual.
Let's move on to the bearings. Wheel hub wear is the most common cause of system failure. You still need to clean them from dirt with kerosene and check them by shaking them. If they are faulty, it will be revealed immediately. It is necessary to replace worn elements and check the operation of the sensor with a multimeter.

ABS block repair

When inspection and cleaning of the sensor parts did not produce results, then perhaps the problem lies in the protection relay, which, as we know, protects electronic circuits from voltage fluctuations in the vehicle’s on-board network.

Finding a protective relay is easy if you have the electrical diagram of the machine on hand. The relay walls are most often made of aluminum, and the cover is made of plastic.

Under the cover there are two or one fuses that may simply blow out, then they need to be replaced.

If this is not the case, then perhaps the pressure drops have damaged the protective relay itself. To diagnose it, we take the tester again and go through the points:

We disconnect the connector from the electrical unit, which is located near the relay. The standard connector has 25 pins.
We put the tester in the voltmeter position.
We connect its probes to the first and second pins of the block. It is easy to confuse them, since they are numbered.
With the ignition switch on, we measure the twenty-volt voltage of the on-board network.
If there is no voltage, then check the integrity of the fuses and check the negative connector number two for connection to the machine ground.

When no problems are identified in this part, we proceed to checking the relay itself. It is necessary to remove the protective relay from the car and connect two wires from the battery terminals to the relay terminals marked 5 and 6. The working relay, when connected to 12 volts, will make clicks; when they do not, you need to replace it.

Replacing the ABS sensor

Alternatively, the ABS system can be checked using an ELM-327 scanner .

An induction type sensor is an induction coil paired with a toothed metal disk located above an impulse rotor connected to the drive shaft or wheel hub.

If the sensor is broken, you can find out with a tester, a soldering iron , or repair pin Next, proceed to measuring the resistance voltage in the node.

Around the pole core there is a winding connected to the magnet. This proximity allows the magnetic field to freely pass to the inductor.

And since the rotor rotates and the interdental cavities change, the magnetic flux passing through the winding core changes. Such changes create alternating voltage, the level of which must be measured.

The voltage frequency and amplitude depend on the number of wheel revolutions.

The pins are attached to the connectors, and the tester measures the resistance of the abs sensor. When measuring, the resistance rate is within 800-1200 ohms , but it is better to look at the passport and check with the permissible unit.

When the network increases to infinity, a network break has occurred, and if the resistance shows zero, then a short circuit has occurred in the sensor circuit. To conduct a complete diagnosis of the sensors, you need to test all the wiring of the device with a tester.

When everything is normal the readings will be like this:

insulation resistance level – more than 20 kOhm ;
leg – front right abs sensor 7-25 Ohm ;
leg – rear right ABS sensor 6–24 Ohm .

When a breakdown is detected during inspection of the sensor, there is no point in repairing it. If a malfunction is not found, then it is not recommended to interfere with the operation of the central unit yourself. Technicians will review the fault codes previously stored in the device and take appropriate action.

Source: http://sibloma.ru/avtoremont-i-tyuning/diagnostika-abs-svoimi-rukami-neispravnosti-i-ix-prichiny

Diagnostics and repair of ABC - anti-lock brake system of foreign cars

Diagnostics and repair of ABS - anti-lock braking system of foreign cars, using the example of Mercedes cars. But the article will also be useful to owners of other foreign cars, including motorcycles, since the operating principle of many systems is the same.

Having bought an imported car stuffed with electronics, many drivers cannot get enough of its comfort and convenience until something breaks down.

And here certain difficulties begin, from which some drivers begin to think about whether to go back to the good old and very simple Zhiguli. After all, the garage master Uncle Vasya, through whose hands an army of domestic cars passed, will no longer help here.

And many repairmen of inexpensive car services often shrug their shoulders when some electronic system fails. And in large car repair shops, just for troubleshooting, the cost of diagnostics can unpleasantly surprise a not very wealthy driver.

Well, if some electronic unit burns out, then the price of a new one can be thousands of dollars, that is, half the cost of the entire machine. But is everything so complicated in a foreign car? Consider, for example, troubleshooting the ABS system.

I have already written about the design of the anti-lock braking system (ABS), and those interested can read about it in detail here. When starting the engine of a car equipped with an anti-lock brake system, the indicator light for this system on the instrument panel lights up and goes out after about 6 to 10 seconds, notifying the driver that everything is in order with the system.

But let’s say that you are driving a car along the road, and while driving, this light flashes on the instrument panel and does not think of going out.

This means that the anti-lock brakes no longer work, but your brakes are fine, just like on a regular older car.

Only now, with sharp braking, especially on a slippery road, the wheels will lock and the car will go into an uncontrollable skid, which can lead to dire consequences.

And a driver who is accustomed to a working ABS system will typically apply the brakes more forcefully than a driver driving an older car without the system.

This means you need to either get used to using your foot more smoothly when braking (which can be useless on a slippery road), or restore the functionality of the ABS.

Naturally, it is better to try to find the reason for the failure of the anti-lock system, which has saved the lives of many drivers, especially beginners.

Before troubleshooting, first remember if you have changed the tires on the wheels of your car. Indeed, often, when replacing summer tires with studded winter tires, some drivers, in order to save money, install winter tires only on the drive wheels, for example the rear ones, and they turn out to be slightly larger in diameter than they are on the front axle of the car.

This means that now the front and rear wheels will begin to rotate at different speeds when the car is moving, and this circumstance, in most cases, can cause the light on the dashboard to light up.

In addition, the light may come on in other cases, for example, when, while driving through mud, sand or snow, your car lies on its belly and has been skidding helplessly for 5-10 minutes.

In such cases, the light necessarily turns on, and it can also light up if the brake light switch (rear brake light switch) is faulty.

But as a rule, in the cases described above, the light does not burn for long, or periodically flashes and goes out.

But if, nevertheless, the lamp lights up on the dashboard and is constantly on, this means that the ABS system is not working (it has turned off). In this case, each driver must decide for himself whether to get used to pressing the brakes more smoothly, or to still restore the functionality of the system, which will significantly increase the safety of the driver and others, especially on slippery roads.

Diagnose the ABS system yourself.

I want to immediately warn drivers not to be afraid of large monetary costs for repairs, since the most expensive part - the control unit (brains) of the system - very rarely fails. This is facilitated by a special relay, which on many foreign cars protects not only the ABS control unit, but also other important electronic circuits.

Therefore, in most cases, the culprits of problems are less expensive parts, that is, special sensor devices - sensors that are located very close to the rotating parts of the wheel (next to the hub).

Moreover, the sensors operate in unfavorable conditions, since in bad weather they can be washed by streams of dirty water. And brake wear products also usually end up on the sensors, covering them with a coating that is difficult to wash off.

It is better to start diagnostics with the front wheels. First, remove the sensor (see Figure 1) and wash it from dirt and brake wear products. You can first wash it with a damp rag (dirt), and then moisten the rag with kerosene or white spirit and use it to wash away deposits that are difficult to wash off.

After removing the sensor, through the resulting window (the socket in which the sensor was located), we carefully examine the teeth on the wheel hub.

Using these teeth, the sensor (sensor) accurately reads the revolutions of the wheel of a car or motorcycle, and if these teeth are clogged with dirt, the sensor will lose count and the readings will naturally be read incorrectly, and this causes the system to fail (or fail).

Therefore, the teeth and sensors of all wheels must be washed from dirt (including the sensor installed in the reverse gear).

After washing the parts from dirt, you next need to check the electrical resistance of the sensors disconnected from the plugs. To do this, set the multimeter to ohmmeter mode (measure resistance) and connect the probes to the connector of each sensor and measure the resistance.

What the sensor resistance of your particular car should be can be found in the factory reference literature for your car.

The front wheel sensors of Mercedes have a resistance in the range of 1.1 - 2.3 kOhm, and the resistance of the rear wheel sensors is approximately 0.6 - 1.6 kOhm.

If you cannot find literature that contains the resistance of the sensors of your particular car, then I advise you to go to a car store, taking a multimeter (tester) with you.

Ask the seller to show you new sensors specifically for your car or motorcycle model, and after measuring the resistance of the new sensors (front and rear wheels), record the readings and then compare these readings with the standard sensors installed on your car.

After checking the resistance of the sensors, you need to switch the multimeter to the voltmeter position, which measures alternating voltage. Next, you should jack up the car and then spin the wheel by hand, while measuring the alternating voltage that appears in the sensor winding when the wheel rotates. The sensor structure is shown in Figure 2.

When the wheel is rotating, the alternating voltage must be at least 100 mV (for Mercedes). If the voltage on your car is less than the specified value, then the sensor should be replaced with a new one (for each make of car, look for the voltage value in the manual of your car or motorcycle).

But there is one more thing to consider. The most common cause of system failure may be dirt or wear on the wheel bearings.

Therefore, before looking for a replacement sensor, wash everything from dirt as described above and check the bearings of your wheel hub by shaking the hanging wheel with your hands.

If they are worn out, replace them, and after replacing the wheel bearings, recheck the sensor with a multimeter.

If, after washing the parts (sensors and teeth) from dirt and checking them with a multimeter, it turns out that all the parts are working, but the light on the panel continues to light, then the protection relay may have tripped. The relay protects the electronic circuits of the ABS system from voltage fluctuations in the vehicle's on-board network (the relay is shown in the photo on the left).

If the relay is triggered, then the engine may begin to start poorly, or run unstably at idle speed (maybe both).

In this case, many people believe that the electronic unit has failed, but the cause of the problem is actually very simple.

For example, the battery is discharged to 10 - 10.5 volts, or, on the contrary, there is a sharp increase in on-board voltage (more often happens when lighting a cigarette from another car).

Finding a protective relay on any car is not at all difficult if you have the electrical diagram of your car or motorcycle. On Mercedes cars, the protection relay is installed behind the battery (under the plastic shield).

The relay body is most often made of aluminum, and the cover is made of transparent plastic. Under this transparent cover there are a pair of fuses (there is only one).

Look under the cap and check the fuses, most likely they are blown, naturally they need to be replaced.

It happens that replacing fuses does not help, because power surges have damaged the relay itself. To check it, you will again need a multimeter (tester).

Before checking, you need to disconnect the connector (usually it has 25 pins) from the electronic unit, which is most often located near the protective relay. Next, set the multimeter to voltmeter mode to measure DC voltage.

We connect the multimeter probes to the 1st and 2nd pins of the electronic unit (they are numbered) and measure the presence of 12 volt on-board voltage on them (of course, with the ignition switch on).

If there is no voltage of 12 volts at terminals 1 and 2, check the fuses again, and if they are intact, then check connector number 2 with a tester (continuity tester) to see if it is connected to the ground (minus) of the car. If not connected, then connect ground to it with a separate wire from the car body (or from the negative terminal of the battery).

If this does not help, then you need to check the protective relay itself. Remove the relay from the car and connect a pair of wires from the battery terminals to relay terminals numbered 5 and 6. A working relay, when 12 volts are applied to terminals 5 and 6, will make characteristic clicks. If you don’t hear clicks, then go to the store for a new relay (taking the faulty relay as a sample).

I hope that after the checks described above and the replacement of failed parts, finally the lamp on the instrument panel no longer lights up.

And this means that the anti-lock brake system on your car is working again, and prevents dangerous skidding, even on slippery roads.

And in order to prevent a subsequent recurrence of ABS failures, you should remember the tips written below, which are not at all difficult to follow.

Tips for drivers to help avoid ABS malfunctions.

Do not allow the battery terminals to oxidize; a special lubricant is sold to prevent this.
Securely tighten the terminals on the battery pole posts with a wrench, and cover the positive terminal with a plastic cover.
When the engine is running or the ignition switch is turned on, do not under any circumstances disconnect various electrical plugs (connectors), except those that the instructions for your specific car or motorcycle model allow you to disconnect.
Frequently check that the wires are securely attached to the generator terminals and that the terminals are clean, as poor electrical contact can cause unwanted surges in the machine’s on-board voltage.
Before welding work on the body, be sure to remove both the negative and positive terminals from the battery posts.
When charging your battery directly on the car, using a charger, also remove both wires (both positive and negative) from the pole posts of the battery, and fasten them securely so that they do not accidentally fall on the battery posts (watch out for this when welding ).

I hope that this article will be useful to those drivers who have decided to independently diagnose and repair the anti-lock brake system (ABS) of their car or motorcycle, good luck to everyone.

Source: http://suvorov-castom.ru/diagnostika-i-remont-avs-antiblokirovochnoj-sistemy-tormozov-inomarki/