Diagnostics of the anti-lock braking system ABS

The most intense way of braking is skidding. But the main disadvantage of braking with a complete blocking of all four wheels is the uncontrollability of the car at the time of braking. At the same time, the question: how to check the ABS and have it serviceable becomes especially relevant.

With this, the car goes into a skid. This effect is especially felt on a slippery road (asphalt wet after rain, a road covered with light ice in the autumn-spring period), a dirt road. You can get out of a skid by releasing the brake pedal. Drivers of non-ABS vehicles use intermittent braking by depressing and releasing the brake pedal to prevent the vehicle from drifting into an uncontrolled skid.

In driving schools, novice drivers are also taught intermittent braking.

But this method is well applicable in predictable situations and bad in emergency situations when emergency braking is required. There is no time for frills.

In addition, braking systems not equipped with ABS have a large variation in braking force. That is, it may well turn out that the front right wheel is completely blocked by brake pads, and the other three wheels are still not completely blocked. The consequences of such a scatter are an attempt by the car to spin around a locked wheel. Which on a slippery road will definitely lead to a sharp skid of the car.

ABS controls the angular speed of the wheel, and if one wheel is blocked by the pads earlier than the others, the system simply unlocks it and equalizes the braking force.

How does a skid happen?

When the car is in motion, they adhere to the road surface due to the force of friction. Excess moisture under the wheels is removed into the gaps of the tread. When braking hard, the tire tread begins to slip on the road surface. At this moment, everything that falls under the wheels of a car can play a fatal role. This is not only a pebble, but also ice under the wheel and just moisture from the rain.

If a spinning wheel jumps over a pebble, then when the wheel is locked, it will play the role of a stop and create unnecessary resistance, an anchor around which the car will tend to turn around. And since the movement is the mass multiplied by the acceleration, then it is enough just to start skidding, everything else in the accident will be done by the force of inertia.

The same is true if under the wheels on one side there is clean asphalt, and under the wheels on the other side there is a crust of ice. But even on dry pavement, the car will definitely spin due to the difference in wheel load. So the problem of directional stability appeared along with the invention of the automobile.

The essence of ABS

Engineers have developed an anti blocking system. Modern anti-lock braking systems prevent complete blocking of the wheels during braking, which ensures vehicle directional stability.

ABS, allows no more than 13% slippage of tires on the road surface when the wheels are blocked.

But the anti-lock braking system can be adjusted independently, according to your preferences and driving style. The driver does not need to “play” with the brake pedal, take into account the condition of the road surface. It does not require any special ones, ABS will do everything itself.

Now, anti-lock braking systems are installed on almost all modes of transport, with the exception of rail. ABS is also used in passenger aviation, where uncontrolled skidding with additional braking by the wheels can lead to a guaranteed departure of the aircraft from the runway.

What is an anti-lock braking system

It consists of electric valves, modulators and an electronic data processing unit. Electromagnetic sensors read the angular speed of the wheel and send pulses to the electronic processing unit. Depending on the readings, the electronic unit through the modulators opens or closes the solenoid valves built into the brake system, which controls the fluid pressure.

Now, all modern cars are equipped with an anti-lock braking system and you probably can’t find a driver who doesn’t understand how important it is to prevent a car from going into an uncontrolled skid when braking. As well as the importance of how to check the operation of the ABS and its functions.

ABS faults

A slight crackle when pressing the brake pedal is rather the norm. You hear the work of modulators. If the ABS is faulty, a warning light will illuminate on the instrument panel.

If the system is working, it lights up when the ignition is turned on and goes out when the engine is started.

The ABS signal glowing while the engine is running is a sign of a system malfunction.

There are four ABS fault conditions in total:

1. Error detection during self-test and ABS off. Critical error in the controller unit or breaks in the sensor harnesses. Angular velocity measurement signals are not read.
2. ABS turns on, successfully passes the self-test and turns off. Breakage in wiring harnesses, poor “Plus” or “Ground” contact, oxidation of contacts at the junctions, breakage of the power wire or controller ground, short circuit of the sensor to ground.
3. ABS turns on, passes self-test, finds an error, but continues to work. Most often caused by a break in any one sensor. Information about the angular velocity of the wheel is taken from an additional sensor. Also, such a malfunction can be caused by different tire pressures or different tread patterns. ABS. A flat tire, or a rougher tread than the other three wheels, will always slow the wheel down a little while driving. The same is true for the wheels installed on the car with varying degrees of tire wear.
4. ABS does not turn on. Critical errors caused by a break in the wiring harness from the sensors, a broken wire near the sensor, worn hub bearings, play or breaks in the wheel sensor rotor (comb).

How is it treated?

Check the degree of wear of the tires of the wheels. Check tire pressure. It must be the same. Check the play of the hub bearings, the condition of the wheel sensor rotor (comb).

In case of severe contamination of the “comb”, clean it with a brush dipped in kerosene. As a rule, the "comb" is available for cleaning even with the wheel removed in "near home" conditions. Access from a lift or from a car pit is not difficult.

If the comb is chipped, replace it. Check the condition of the wires to the sensors. Check the condition of the sensors (serviceability, short to ground). If the listed procedures did not give any result, then, most likely, the matter is in electronics. But as practice shows, mechanical parts fail much more often than electronics. In order not to sort through all the possible causes of breakdowns in sequence, for accurate diagnosis it is desirable to obtain an error code.

Some blocks do not remember error codes and must be diagnosed during operation.

ABS Diagnostics

Currently, blocks can exchange either fast or slow codes. There are diagnostic adapters for blocks with quick codes.

Reading information starts when the ignition is switched on. Then everything is simple. See the manual for a description of the error code. Unfortunately, there are situations when the unit turns on, but does not respond to the poll. Then you will have to look for manuals for your block, read the description and ring the necessary circuits. You may have to open the control unit and solder the diagnostic adapter to the controller board itself.

Slow codes

Control units with slow codes p/n 535 907 379 have an additional gray diagnostic connector. The socket we need in this connector is called L-Line. It is marked, its location on the chip can be found in the manual or specification. For slow code diagnostics, an appropriate adapter can be purchased. It is equipped with an LED, a series of flashes of which will allow you to determine the fault code. But you can do without this device.

The easiest way to check the ABS and get trouble codes is with the "ABS Fault" light on the instrument panel. We take two wires. We securely fasten one to the "mass". We connect the second to the chip (it is gray), to the L-Line output. Turn on the ignition and jumper the wires for 4 seconds. Turn off the ignition and open the wires. The "ABS fault" signal on the instrument panel starts flashing. This at least indicates that the block has responded.

The first signal will always be "0". This is a 3 second light signal. It will be followed by a series of flashes with an interval of 1 second, which is the error code. The code is a four-digit (four-digit) number.

Each series of flashes, separated by a three-second pause, is a digit in the discharge.

For example: three flashes in a row with a long pause will mean the number 3. Five flashes and a long pause - 5, etc. After four series of flashes separated by pauses, a long light signal “0” will follow. We count the number of flashes between long pauses and write the discharge on paper. The result is a code. Something like - 5324. After that, the code will be repeated again.

To find out the next code, it is necessary to close the wires connected to the chip and to the ground during the “0” signal. The list of errors ends with four successive long light signals "0".

A list of error codes in English can be found at VORM. There is a Russian-language list from the VAG concern, but it is less complete.

The ABS controller does not take into account the number of errors. If, during the poll, 3 errors were generated from the front left wheel and one from the rear right wheel, the controller will display a message about two errors, not four.

Checking the ABS sensor

The easiest method is to drive the car to a car service. But if this is not for you and you like to get to everything on your own, then prepare:

• tester;
• soldering iron;
• heat shrink tape;
• repair pins.

Must be posted. According to the service manual, remove the housings of the control units and controller connectors. This must be done in accordance with the manual, since each model has its own characteristics.

We connect the pins to the sensor connectors and measure the resistance with a tester.

The resistance of a good sensor should be within 1 Kom. Although it will not be superfluous to look at the description of the limits of permissible resistance on your model. You also need to check for a short to ground.

When the wheel is rotated by hand, the resistance of the sensor should change.

If the resistance of the sensor is within the limits specified in the manual and the sensor responds to the rotation of the wheel, then it is alive and well.

If you find a wire break or short to ground, repair the problem. Connection of wires should be carried out only by soldering. This will ensure the reliability of fastening and the absence of oxides appearing in places of ordinary twists and, accordingly, will reduce the resistance of the current passing through the junction.

The sensor has a polarity, so you need to connect the wires in accordance with the marking or color of the wires specified in the manual. There is an easier option. Before removing the wires, mark them according to the polarity of the connection.

Insulate the soldering area with heat-shrinkable insulating tape. Do this procedure for the rest of the wheels.

Conclusion!

Activities such as checking and adjusting the ABS are more often carried out when malfunctions occur. However, experts recommend doing this procedure regularly.

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