Useful Tips

On fire - ABS: Diagnostics of a malfunction of the brake system


The brake system requires close attention. Do not use a vehicle with a faulty brake system. Therefore, each motorist must know the main malfunctions of the brake system and identify them by external signs. This article discusses the main malfunctions of the hydraulic working brake system of a car.

In accordance with the design of the brake system, malfunctions can be conditionally divided into malfunctions of the brake mechanism, malfunctions of the brake drive and malfunctions of the brake booster.

Distinguish the following disc brake malfunctions:

  • wear, damage or contamination (oiling) brake pads,
  • wear, deformation, seizure on the surface of the brake discs,
  • loosening of the mount, deformation of the caliper.

The main brake failure include:

  • jamming of the piston of the working cylinder,
  • brake fluid leak in the working cylinder,
  • jamming of the piston of the main cylinder,
  • brake fluid leak in the master cylinder,
  • damage or clogging of hoses, pipelines,
  • air leaks in the system due to loosening of the mount.

The vacuum brake booster may have the following problems:

  • insufficient discharge in the intake manifold,
  • damage to the vacuum hose,
  • amplifier follower valve malfunction.

All of the listed malfunctions of the brake system to a greater or lesser extent reduce the braking performance of the car, therefore they are dangerous for all participants in the movement.

Causes of brake malfunctions are:

  • violation of the rules of operation of the brake system (violation of the frequency of maintenance, the use of low-quality brake fluid),
  • low quality of components,
  • ultimate service life of system elements,
  • exposure to various external factors.

The malfunction of the brake system is indicated by various deviations from normal operation, the so-called external symptoms of malfunctions, which include:

  • deviation from rectilinear movement during braking,
  • large stroke of the brake pedal
  • grinding when braking,
  • screech, whistle when braking,
  • reduced pedal effort when braking,
  • increased pedal effort when braking,
  • pedal vibration when braking (not to be confused with pedal pulsation when operating the ABS system),
  • low brake fluid in the reservoir.

To facilitate monitoring of the state of the brake system in the design of the car, various sensors are used. The measurement results by sensors of the system parameters are displayed in the form of signals of the corresponding lamps on the dashboard, the readings of the on-board computer. On a modern car, the following brake lights:

  • low brake fluid
  • brake pad wear
  • ABS system malfunctions,
  • ESP system malfunctions (ASR).

To establish specific malfunctions of active safety systems, computer diagnostics of the car is used.

How to find out what happened to the anti-lock braking system?

Before the appearance of the "ABS" system in automobiles in the 70s of the 20th century, those systems were less safe when compared with today's modern cars. This was especially true of the moment when the driver had to move either on a wet or on a snowy icy road. In those years, old cars were usually equipped with not very high-quality wheels (tires), not quite reliable rear-wheel drive, as well as a regular and simple brake system without any electronics. But today, as you know friends, everything has changed for the better. Nowadays, most of the drivers do not even think about the modern brake systems that are on the machines. Today, each of us (drivers) feels confident and reliable behind the wheel of a car, even when driving on a road that is covered with snow a few centimeters or is specifically icy. The thing is as follows. Most modern cars in our time are equipped (equipped) with front-wheel drive, which gives drivers confidence when they are driving a car. Moreover, these cars are also equipped with the latest modern electronic safety systems that control the grip of the car with the road surface, and excellent modern rubber, which demonstrates on the slippery road just some miracles of adhesion to such a track. One of the most important systems in any modern car today is the anti-lock braking system (ABS), which significantly reduces the braking distance of the car and prevents the wheels from locking, which can lead to loss of traction and therefore further to skidding.

The ABS system has already become standard equipment in the automotive industry; today it is installed on virtually every modern car manufactured by car manufacturers. As we have written more than once, this "ABS" system consists of several parts, namely, speed sensors that are installed specifically on the wheels of the machine, an electronic control unit for the anti-lock braking system, and also hydraulic valves, which are detected by a specific signal from the electronic unit here - they also regulate a certain braking force in each wheel without resorting to the driver’s help (without his participation).

Wheel sensors "ABS" monitor the speed of rotation of each wheel of the car and constantly transmit data to the auto-computer. As soon as the ABS system unit begins to notice (see) that the wheel stops spinning, it immediately activates the hydraulic brake system valves and it, in turn, immediately begins to reduce the brake pressure in this wheel itself. As a result, the pressure of the brake fluid in the wheel immediately drops and the braking force decreases, which further contributes to the unlocking of the wheel and the return of traction. This process is repeated several times per second through the machine’s computer until the car stops completely or the driver himself releases the brake pedal.

The ABS control unit and the car computer each time the ignition is turned on automatically conducts a self-test of the anti-lock brake system. That is, every time you start a car, an automatic test of the ABS system takes place immediately. In the event that during the self-test the auto-computer does not receive enough data from the sensors, from the ABS control unit and from the hydraulic valves of the brake system, the signal lamp with the “ABS” symbol lights up on the car dashboard. For example, let’s say if the car’s computer or the same ABS control unit did not receive a return signal from the hydraulic pump of the brake system or from the same valve installed on each wheel, then the signal “ABS error” will immediately light up on the tidy (on the panel), - in the form of an icon (indicator).

Pay friends your attention specifically to that, in spite of the malfunction of the ABS system and the appearance of its burning “ABS signal-sign” in the car itself, as a rule, the mechanical brake system continues to work and you can safely without fear of continuing to drive the car, but already without this electronic system to help lock the wheels during braking. That is, in other words, we can say that if the ABS system breaks down, you can safely use your car. True, in this case, you must be extremely careful when braking on a wet, snowy or slippery road, since without this "ABS" system the wheels of your car may lock up periodically. Therefore, friends, we do not recommend you to operate your machine without a corresponding repair for a long time in the event of an ABS system malfunction. Thus, it should be clear to all drivers that in the event an auto-computer issues an “ABS system error”, it is necessary to establish the cause of this malfunction as soon as possible and eliminate it as soon as possible.

Malfunction of the ABS system.

And so let's say. In your car, on the dashboard the signal lamp or the icon warning you about problems with the anti-lock brake system lights up. What should be done in this case?

First, first you need to make sure that the illuminated indicator icon indicates exactly the problem with the "ABS system", and not the malfunction of the entire brake system of the car.

To do this, you must carefully listen to your car when braking and turn your attention to the brake pedal. If during braking you started to hear extraneous noises (whistles, knocks, creaks, etc. sounds) or the brake pedal in the car became too soft (softer than usual), then your task is the direct road to the technical auto center, where specialists must conduct a thorough diagnosis of the entire braking system of the machine. Please remember that all these signs indicate a serious malfunction of the entire brake system of the car, which can lead you to traffic accidents. Therefore, friends, remember, if the brakes of your car have become very bad, soft and not quite ordinary, we do not recommend that you take the public road with such brakes, as this can be very dangerous. In this case, you must call the tow truck.

Also, in order to specifically find out that the illuminated "ABS" symbol icon of the malfunction was the cause of the anti-lock braking system of the car, you also need to make sure that there is no air in the braking system of the car, that the brake pedal on the car is still stiff, and not too soft, and still make sure that the brake system is not leaking brake fluid. To do this, you must first check the brake fluid level in the tank, and then only all the brake pipes and hoses for their depressurization or breakage.

In addition to everything else, one must remember that when the ignition is turned on, having seen such an illuminated "ABS symbol icon" on the dashboard, one should never panic. Maybe this is just a common mistake of the car’s electronics. Therefore, in such a situation, turn off the ignition and remove the key from the lock, and then turn on the ignition again and check again if the "ABS icon symbol" appears again on the tidy (panel). Repeat this process several times. It is possible that this is really a car computer error and after several such ignition on and off, this “ABS” system error will simply disappear.

If, nevertheless, after several attempts to turn the ignition on and off, this “ABS” system error on the dashboard does not disappear, that is, it does not disappear, then you have two options:

The first is to go to a car service and conduct a thorough computer diagnostics of the entire car. The main feature of the ABS system diagnostics is the following, that is, in the electronic interrogation of the ABS unit with the help of special equipment for all kinds of errors in its system.

With the help of such diagnostics, a specialist will be able to quickly determine the "error code" in the "ABS" system, which specifically led to the appearance of an alarm "ABS symbol icon" on the dashboard.

Also, this same "error code" will give a specific hint where exactly you need to look for the cause of the malfunction of the entire "ABS" system.

The second option is needed only for those drivers who want to get to the bottom of this truth on their own and on their own. In order not to use (not use) the expensive diagnostic equipment for testing the "ABS" system, you need a service manual for your car (a book on the repair and maintenance of your car model), also a simple car tool that is sold in any car shop and naturally a multimeter high impedance (high impedance). If you can’t find the necessary book on repairing your car model for sale, please search for it on the Internet or download it to your computer or smartphone.

Friends, we draw your attention to the following, that in some cars you can get direct access to the diagnosis of the same "trouble codes" that are stored in the car's computer, and all this without using a special diagnostic scanner. To do this, you need to check each electronic unit of your car (including the "ABS" control unit) using the old proven method, namely, using two simple wires that you must connect to the corresponding connectors on the electronic systems of the car. For example, you can connect these two wires to check the circuit closure in the same “ABS” control unit, for which you need to connect these two wires directly to the “ABS” control unit connector and close the wires with a pin or a regular paper clip. If after this procedure the error of the “ABS symbol icon” disappears from the dashboard, the cause of such an error is located in the control unit for the anti-lock brake system. In the same way, in the same way, you can connect with a paper clip or pin and without using wires, other specific and necessary contacts.

If, dear motorists, your car is equipped with a more modern computer, where the diagnosis of error detection is carried out only by connecting the scanner to the diagnostic port "OBD II" (On-Board Diagnostic), then to establish the cause of the "ABS symbol icon" on the dashboard, you you will need only electronic diagnostics, which you can do either in the technical center, or yourself, but with the help of the inexpensive error scanner you purchased to the "OBD II" port.

Suppose the following, that you do not have any information about errors in the car computer, which led to the appearance of the “ABS symbol icon” on the dashboard. Do not rush to conduct computer diagnostics. First, check the fuse for the ABS control unit yourself. Indeed, the common cause of a malfunction of the "ABS" system is the usual failure of a fuse in the control unit of the anti-lock brake system.

And so we follow further, you checked a safety lock of the control unit "ABS" which appeared to be in working condition. What to do now? And now you have to use a multimeter to check the voltage and resistance in all electronic parts of the "ABS" system. To do this, read the manual for the operation and repair of your car, namely, with all the relevant control voltage values ​​and the corresponding resistance in the sensors "ABS" and in the electronic unit "ABS".

True, we must not forget to check the main wiring harness that is connected to the ABS control unit before this. Carefully inspect the entire wiring harness responsible for the operation of the entire ABS system for damage. Also, pull the connector of this wiring harness out of the "ABS" control unit and carefully inspect all the contacts in the connector for contamination or oxidation. All contacts on the wires in the harness must be clean. If the contacts need to be cleaned, use a special aerosol spray to clean the electrical contacts and connectors, take and clean the connector from this contamination.

Also, when inspecting the contacts of the ABS harness connector, pay attention to contact corrosion.Please remember that even microscopic oxidation and corrosion chemicals can seriously affect the resistance in the electrical circuit of the ABS system. By wires, as many people know, a small voltage of electricity (millivolts) is transmitted and even the slightest increase in resistance due to contamination of the connector contacts can lead to malfunction of the entire electronic part of the ABS system, and also cause an error in this system, which leads to lights on the dashboard display "ABS".

If the ABS system controller looks complete and in working condition, and disconnecting the ABS system wiring harness connector from the anti-lock brake system unit did not help you solve the problem of the burning "ABS symbol icon" on the dashboard, then it is time to check the speed sensors wheels that transmit information to the ABS control unit. To do this, you must initially measure the resistance of these sensors, comparing them with the reference values ​​specified in the repair manual for your car.

If this resistance is within acceptable standards, then proceed to a visual inspection of the wheel speed sensors themselves, the wires themselves suitable for them and to inspect (inspect) the state of each axis of the gear gear (or on each wheel hub) that are installed on the wheel of the machine . As a rule, similar sensors related to mechanical sensors were installed on old cars.

Also, today, in many modern cars, sensors are currently used that need electricity. As a rule, "ABS sensors" based on the "Hall effect" (a semiconductor wafer is installed inside the sensor) are used, which, when interacting with a magnetic ring on the wheel hub, record a change in the magnetic field itself and the rate of electron formation on the plate inside the "ABS sensors".

Unfortunately, not in all cars these "ABS sensors" and wires through which the signal from the sensors is sent to the "ABS" control unit are reliably protected from the aggressive external environment. Ultimately, these wires and sensors can fail due to damage and dirt getting on them.

In order to check the condition of the wheel speed sensors and the ABS system wires, it is necessary to start by removing the wheels from the machine, namely, lifting the machine one at a time from the right side and removing each wheel.

So you get free access to sensors and wires.

If, while inspecting the "ABS" system wiring harness and wheel speed sensors, you find any damage (or the wheel speed sensor is not securely attached or it is loose), then you can assume that you found the cause of the error on the dashboard, which I informed you about the ABS system malfunction.

But if, when inspecting these wires and the "ABS sensors", you did not find any external damage on them, then remove all the "ABS" system speed sensors from the hub (or from the axis) and check their resistance, as we said, with a multimeter ( if you have not done this before). Control resistance values ​​in wheel speed sensors can be found in special books on the repair and operation of your car model.

We also advise all car owners to inspect the wires of the ABS wheel rotation sensors from time to time, do this even if the anti-lock braking system of the machine is working properly and the “ABS symbol icon” does not light up on the dashboard. Here's the thing: all wires and wheel rotation sensors are located at the bottom of the car and they are constantly exposed to aggressive environmental influences. Remember friends, that the main enemy for wires and sensors is salt, which is found in road reagents, in water and in snow.

For what reasons does the “ABS” indicator on the dashboard light up if the sensors and the control unit with wires of the “ABS system” are working?

If after testing you find that all electronic parts of the "ABS system" are in good condition, and the "ABS symbol icon" on the dashboard is still lit, then most likely the problem itself is connected to the hydraulic valve system of the "ABS system", which unfortunately not subject to partial repair.

In this case, you need to contact the technical center in any way for diagnostics of the hydraulic brake system of your car and possible subsequent repairs. We also advise you to remove the hydraulic "ABS block" and test it yourself yourself with the help of special equipment, using specialized literature. Good luck friends!