ABS performs the following functions:
- Improving driving stability when avoiding obstacles, even during braking.
- Reduced stopping distance during heavy braking while maintaining vehicle stability and control even when cornering.
The anti-lock braking system works based on information from four sensors transmitted to the ABS unit. The system controls each wheel individually and reduces the fluid pressure in the wheel brake mechanism, the wheel of which begins to block.
Under normal conditions, the standard brake system applies the brakes until a wheel lock is detected by the ABS control unit. When the ABS control unit detects a blocked wheel, it controls each valve to increase or decrease the pressure.
The ABS control unit determines the speed and deceleration rate of each wheel based on information from the wheel speed sensors. When braking, the wheel speed decreases and the ABS unit detects the difference between the vehicle speed and the wheel speed. If the deceleration of some wheels exceeds the expected value, the ABS unit detects the start of a blockage and opens the appropriate solenoid valves to reduce the brake fluid pressure. In this case, the wheel speed increases and the pressure relief solenoid valve closes and the brake fluid pressure in the working brake cylinder of the corresponding wheel increases.
ABS hydraulic system: 1 – the brake pipeline of the right forward wheel; 2 – the brake pipeline of the left forward wheel; 3 – the brake pipeline of the right back wheel; 4 – the brake pipeline of the left back wheel; 5 – a brake hose of the right forward wheel; 6 – a brake hose of the left forward wheel; 7 – a brake hose of the right back wheel; 8 - brake hose of the left rear wheel; 9 - hydroelectronic ABS control unit (GEBU); 10 - vacuum brake booster and master brake cylinder
EBD (Electronic brake force distribution)
EBD is additionally used instead of a pressure regulator to perfectly distribute pressure to the front and rear brakes.
- improving the performance of the basic braking system;
- compensation for the difference in friction coefficients;
- abolition of the pressure regulator;
- malfunction signaling by a control lamp.
Pilot lamps
The ABS warning lamp indicates the degree of ABS performance.
The ABS warning lamp lights up in the following cases:
- within 3 s after switching on the ignition;
- in the event of a ban on the operation of ABS in the event of a malfunction;
- if the ECU does not turn on when the ignition is on;
- in diagnostic mode.
The EBD warning light indicates the EBD's health.
The EBD warning lamp lights up in the following cases:
- during initialization after switching on the ignition (3 s);
- in the event of a ban on the operation of EBD in the event of a malfunction;
- if the ECU does not turn on when the ignition is on;
- when the parking brake is applied or the brake fluid level is too low.
Features of the ABS system
Sound when checking the ABS system. When starting the engine, a dull thud is sometimes heard from the engine compartment. It is related to the system health check.
Sound during ABS. The sound of the electric motor of the ABS valve body (howling sound). Scraping sound accompanied by vibration of the brake pedal.
During ABS operation, sounds are emitted from the chassis of the car, which are caused by repeated cycles of braking and releasing the wheels (deaf blows coming from the suspension; tire creaking).
Great stopping distance. On some road surfaces, including snowy or gravel roads, vehicles equipped with ABS may have longer braking distances than usual. Therefore, when driving on such roads, the car owner must be careful and drive at a reduced speed.
Vibration of the brake pedal is normal.
ABS Brake Fault Codes
Cable part of the ABS hydroelectronic control unit connector
The cable part of the connector for the ABS hydro-electronic control unit is shown in the figure. The addressing of the cable part of the ABS hydroelectronic control unit connector is shown in the table.
Contact addressing of the hydroelectronic control unit connector (GEBU) ABS systems
Number contact | Address (contact assignment) | Maximum current | Minimum current | Note |
1 | - | - | - | |
2 | - | - | - | |
3 | - | - | - | |
4 | EBD warning lamp | 30 mA | 5 mA | |
5 | Diagnostic interface | 6 mA | 3 mA | |
6 | Right front wheel sensor | 16 mA | 6 mA | |
7 | Right front wheel sensor | 16 mA | 6 mA | |
8 | Right rear wheel sensor | 16 mA | 6 mA | |
9 | - | - | - | |
10 | Left rear wheel sensor | 16 mA | 6 mA | |
11 | Left front wheel sensor | 16 mA | 6 mA | |
12 | «Weight» | 5-15 A | 2.5 A | ABS control |
13 | Voltage a/b 1 (Lapan food) | 5-15 A | 2 A | ABS control |
14 | Voltage a/b 2 (motor power supply) | 20-39 A | 10 A | ABS control |
15 | «Weight» | 20-39 A | 10 A | ABS control |
16 | - | - | - | |
17 | - | - | - | |
18 | - | - | - | |
19 | - | - | - | |
20 | ABS warning lamp | 30 mA | 5 mA | |
21 | - | | | |
22 | Stop signal switch | 10 mA | 5 mA | |
23 | Right rear wheel sensor | 16 mA | 6 mA | |
24 | Ignition | 1 A | 500 mA | |
25 | Left rear wheel sensor | 16 mA | 6 mA | |
26 | Left front wheel sensor | 16 mA | 6 mA | |
Hydroelectronic control unit (GEBU) ABS
Withdrawal
Remove the air filter and air intake pipe.
GEBU pin connector
Disconnect the GEBU connector with a double lock by pulling it up.
Disconnect the brake pipes from the GEBU.
GEBU bracket mounting bolts (indicated by arrows)
Unscrew the bolts securing the GEBU bracket and remove the GEBU.
The tightening torque of the GEBU bracket mounting bolts is 8–10 Nm.
Attention!
- GEBU disassembly is not allowed.
- It is allowed to transport and store the GEBU in a vertical position with plugged holes.
- Do not drain fluid from the HEBU.
Installation
Install the GEBU in the reverse order of removal.
Tighten the bolts for fastening the GEBU to a torque of 8–10 Nm, the fitting for fastening the brake pipelines to a torque of 13–17 Nm.
Wheel sensor signal voltage test
Put the car on a lift, turn off the parking brake.
Disconnect the GEBU connector and check the contacts of the cable part of the connector.
Note. When checking, remove the double clamp of the contact connector and attach the control device to the wires from the side opposite to the connector contacts. Attaching the measuring probes of the device to the contacts themselves does not provide a reliable connection
Using a tester or oscilloscope, check the signal voltage of the wheel sensors by rotating the corresponding wheel at a speed of 0.5-1 s-1.
Connecting a control device for checking the voltage of the wheel sensors signal
wheel sensor | Connector Pin Numbers |
Left front | 11, 26 |
Right front | 6, 7 |
Left back | 10, 25 |
Right rear | 8, 23 |
Signal voltage when measured with an oscilloscope, V:
- lower level - 0.535 (at 7 mA)
- upper level - 1,050 (at 14 mA)
Wheel speed sensors
Front wheel speed sensor: 1 – contact connector of the front wheel speed sensor; 2 - front wheel speed sensor
Rear wheel speed sensor: 1 - rear wheel speed sensor
Removing the front wheel sensor
Bolt of fastening of the forward wheel sensor
Loosen the front wheel sensor mounting bolt.
In the engine compartment, disconnect the front wheel sensor connector.
Remove the wheel sensor wiring fasteners.
Remove the wheel sensor.
Removing the rear wheel sensor
Disconnect the rear wheel sensor connector at the wheel hub.
Remove the brake drum by unscrewing the screw securing it to the wheel hub.
Remove the four bolts securing the rear wheel hub to the rear suspension beam.
Removing the rear wheel hub
Remove the rear wheel hub through the brake mechanism.
Attention! Do not remove the wheel sensor from the hub with hammer blows, as this may damage the sensor.
Removal of air from a hydraulic drive of brakes
The operation is carried out to effectively remove air from the brake hydraulic drive and fill the hydraulic unit of the anti-lock brake system, brake pipelines and the main brake cylinder with brake fluid.
The HI-SCAN diagnostic tool is used to bleed air from the hydraulic brakes of vehicles equipped with an anti-lock system. During this operation, the device, connected to the diagnostic socket under the instrument panel, controls the solenoid valves and the electric pump of the anti-lock system.
Remove the brake fluid reservoir cap and fill the reservoir with brake fluid.
When topping up, use only DOT-3 or DOT-4 brake fluid.
Attention! If brake fluid gets on the paintwork of the body, immediately wash it off with plenty of water.
Note. When using the special bleeder, do not depress the brake pedal.
Attach a clear plastic hose to the bleeder valve on the wheel cylinder and dip the other end of the hose into a clear container half filled with brake fluid.
Connect the HI-SCAN device to the diagnostic connector located under the instrument panel.
Using the HI-SCAN tool, turn on the electric pump and the solenoid valves of the anti-lock system.
Follow the instructions on the screen of the HI-SCAN.
Attention! To prevent burnout of the motor windings of the anti-lock pump, do not exceed the maximum allowable time of its operation, indicated on the screen of the HI-SCAN device.
Press the brake pedal several times, opening the bleeder valve until air bubbles no longer appear in the fluid flowing out, then tighten the bleeder screw.
Carry out the described operation on the remaining wheels of the vehicle in the following order: rear right wheel (in the direction of the vehicle), front left wheel, rear left wheel, front right wheel.
The moment of an inhaling of unions of prorolling 7–13 Н·м.