Anti-lock braking system (ABS) 8.1 Bosch

Vehicles in optional specification are equipped with the anti-lock braking system (ABS) of the 8.1 series from «Bosch».

The ABS is effective during emergency braking on roads with mixed surfaces (for example, asphalt — ice) and prevents the locking of wheels that are in less favourable grip conditions (on ice), ensuring the minimum braking distance of the vehicle for that road surface while maintaining its stability and steerability.

This ABS has an electronic brake-force distribution (EBD) function, which prevents the locking of the rear wheels that causes rear-axle skidding when braking a partially laden vehicle.

The electrical part of the ABS consists of 4 «Bosch» speed sensors located in the vehicle's wheel assemblies, a «Bosch» hydraulic unit with an integrated electronic control unit in the engine bay on the left, an ABS wiring harness, an ABS power harness, an ABS fault indicator and an EBD fault indicator in the instrument cluster.

ABS configuration for various modifications

On the «GAZelle» vehicle with 4×2 wheel arrangement, the «Bosch» hydraulic unit 0 265 231 980 and the speed sensors are installed:

• 0 265 008 029 — front right;
• 0 265 008 030 — front left;
• 0 265 008 033 — rear left;
• 0 265 008 034 — rear right.

On «GAZelle» vehicles with 4×4 wheel arrangement, the hydraulic unit 0 265 232 204 and the speed sensors are installed:

• 0 265 008 211 — front right/left;
• 0 265 008 033 — rear left;
• 0 265 008 034 — rear right,
• and additionally an acceleration sensor 0 265 005 146 is installed, located on an adapter bracket mounted on the right-hand side of the pedal bracket, as well as a wiring harness connecting the acceleration sensor to the ABS harness.

Fault indication

Each time the ignition is switched on, the ABS fault indicator and the EBD fault indicator come on for about 3 seconds and then go out. This indicates that the electrical components and circuits of the ABS, as well as the EBD system, are serviceable.

A brief illumination of the ABS fault indicator or of the ABS and EBD indicators when starting the engine is permissible.

The ABS and EBD fault indicators also come on if the circuit from the instrument cluster to the electronic control unit is broken.

Important: a permanently illuminated state of the ABS fault indicator (orange) or its illumination while driving indicates an ABS fault that has occurred. The service brake system remains operational as without ABS.

Important: a permanently illuminated state of the ABS fault indicator and the EBD fault indicator (red) or their illumination while driving indicates a fault of the ABS and EBD systems.

Brake ABS diagnostics

Important: on ABS 8.1 (unlike ABS 5.3) there is no possibility of diagnosing the system by the flash codes of the ABS fault indicator.

To carry out diagnostics of ABS 8.1 it is recommended to use the ASKAN-10 diagnostic tester-scanner (manufactured by OOO «NPP ELKAR», Moscow) with the GAZ ABS diagnostic cable, with the ABS 8.1 diagnostic module for «GAZ» vehicles installed.

To carry out ABS diagnostics it is necessary:

• to connect the GAZ ABS diagnostic cable to the quick-release connector of the tester and to the battery;
• with the ignition switch key in position «0», to connect the diagnostic connector to the ABS diagnostic socket of the vehicle.

The diagnostic connector is located on a bracket secured under the attachment point of the windscreen washer reservoir bracket.

• after turning the ignition switch key to position «I» (ignition on), the tester display backlight will come on and a splash screen will appear briefly, followed by the tester main menu.

To test the ABS of «GAZ» vehicles it is necessary to launch the «ABS 8» diagnostic module from the «GAZ» package.

After the module is launched, a brief splash screen will appear on the display, followed by the «MODE» menu.

After the «MODE» menu appears, the green «LINK» LED located on the front panel below the display must come on.

If the red «ERROR» LED located on the front panel below the display comes on, it is necessary to check the correct connection of the diagnostic cable and the integrity of the electrical circuit between the diagnostic socket and the ABS hydraulic unit.

The «MODE» menu contains the following subsections:

• «Control unit description»;
• «Parameters»;
• «Faults»;
• «Hydraulic unit bleeding»;
• «Tests»;
• «Exit».

Subsection «Control unit description»

In the «Control unit description» subsection, the identification parameters of the hydraulic unit are viewed, the coding variant is changed, and information about the diagnostic module is viewed.

In the «Identification» item the identification parameters of the hydraulic unit are viewed:

• factory number of the hydraulic unit;
• manufacturer identifier;
• system name;
• control unit code;
• software code;
• software version;
• coding variant — «Gazelle», «Gazelle 4×4».

In the «Coding variant» item the coding variant corresponding to the model of this vehicle is selected — «Gazelle», «Gazelle 4×4».

The new coding variant is displayed only after exiting the ABS 8 diagnostic module and re-entering this module.

Important: selection of a coding variant that does not correspond to the model of this vehicle is not permitted! The coding variant must be changed only by a specialist!

Selection of the coding variant is mandatory when installing a new hydraulic unit on the vehicle.

If the coding variant is absent (hydraulic unit in as-delivered condition), when viewing the «Coding variant» item a message according to figure 7 will appear on the display.

The absence of a selected coding variant will cause error 4551 to appear in the memory of the hydraulic unit control unit.

It is necessary to change the coding variant in accordance with the model of this vehicle, then erase the existing fault codes using the «Faults» menu.

To select the coding variant, press the «Enter» key and choose the required variant from the offered list of vehicle models (fig. 8).

After selecting the current model, press the «Enter» key. If the above operation is completed successfully, a message will be displayed.

A conventional example of the message displayed is shown in fig. 9.

Important: on vehicles with 4×4 wheel arrangement, changing the coding variant is not provided for and is not available.

In this case, the message «Negative response. This ECU implementation does not support changing the coding variant» will be displayed.

In the «About the program» item, information about the software module of this tester-scanner is viewed. A conventional example of the information displayed is shown in fig. 10.

Subsection «Parameters»

In the «Parameters» subsection, the values of some ABS system parameters are viewed.

The parameter list is divided into parameter pages. The top line contains information about the name and number of the current page and the number of pages.

To go to another parameter page, press the key with the symbol ◄-- or --►.

An extended explanation of each parameter can be read on the tester display by pressing the «F3» key.

To display the graph of the selected parameter on the screen, press the «F2» key.

In the dynamic graph viewing mode, the parameter value can be stopped at any point by pressing the «Enter» key. Pressing the keys with the symbols ◄-- and --► then allows the graphs of the other parameters of this page, stopped at the same point, to be viewed.

The graph is resumed by pressing the «Enter» key again.

To return to the initial parameter window, press the «Esc» key.

The parameter page is saved for subsequent printing by pressing the «Shift» and «F2» keys simultaneously.

Subsection «Faults»

In the «Faults» subsection, current and stored faults are viewed, fault codes are erased, and faults are saved in the tester memory for subsequent printing.

The «Current errors» item allows the codes of current faults (present in the ABS system at the moment) and their description to be viewed.

In the top line of the displayed message is the window title — «Cur. errors», below which is a line with two values.

The first value «4040» indicates the digital fault code, the second — «1/1» indicates the fault sequence number/total number of faults in the ABS system.

This is followed by the fault description. Erasing current faults while viewing current errors is done by pressing the «F3» key.

To save faults for subsequent printing, press the «Shift» and «F2» keys simultaneously.

The «Stored errors» item allows the codes of stored faults (stored in the hydraulic unit memory, not present in the ABS system at the moment) and their description to be viewed.

After the faults have been rectified, the errors accumulated in the memory of the hydraulic unit control unit must be erased.

Erasing stored faults while viewing stored errors is done by pressing the «F3» key.

Possible brake ABS faults, their causes and remedies

4035 — Incorrect signal from the front left wheel speed sensor:

• large gap, more than 1.1 mm, between the sensor and the ABS toothed rotor;
• increased runout, more than 0.21 mm, of the ABS toothed rotor relative to the axis of rotation;
• geometry of the ABS toothed rotor disturbed;
• ABS harness fault, speed sensor fault.

Remedies:

• tighten the sensor mounting bolt to a torque of 7–10 N·m (0.7–1.0 kgf·m), the ABS toothed rotor must not touch the sensor when rotating;
• adjust the hub bearing preload;
• replace the worn hub bearing or replace the hub assembly with bearing and rotor;
• rectify the ABS harness fault or replace the ABS harness;
• replace the speed sensor.

4040 — Incorrect signal from the front right wheel speed sensor:

• large gap, more than 1.1 mm, between the sensor and the ABS toothed rotor;
• increased runout, more than 0.21 mm, of the ABS toothed rotor relative to the axis of rotation;
• geometry of the ABS toothed rotor disturbed;
• ABS harness fault, speed sensor fault.

Remedies:

• tighten the sensor mounting bolt to a torque of 7–10 N·m (0.7–1.0 kgf·m), the ABS toothed rotor must not touch the sensor when rotating;
• adjust the hub bearing preload;
• replace the worn hub bearing or replace the hub assembly with bearing and rotor;
• rectify the ABS harness fault or replace the ABS harness;
• replace the speed sensor.

4045 — Incorrect signal from the rear left wheel speed sensor:

• large gap, more than 1.1 mm, between the sensor and the ABS toothed rotor;
• increased runout, more than 0.21 mm, of the ABS toothed rotor relative to the axis of rotation;
• geometry of the ABS toothed rotor disturbed (absence of two or more teeth, dents);
• ABS harness fault, speed sensor fault.

Remedies:

• tighten the sensor mounting bolt to a torque of 7–10 N·m (0.7–1.0 kgf·m), the ABS toothed rotor must not touch the sensor when rotating;
• adjust the hub bearing preload;
• replace the worn hub bearing or replace the hub assembly with bearing and rotor;
• rectify the ABS harness fault or replace the ABS harness;
• replace the speed sensor.

4050 — Incorrect signal from the rear right wheel speed sensor:

• large gap, more than 1.1 mm, between the sensor and the ABS toothed rotor;
• increased runout, more than 0.21 mm, of the ABS toothed rotor relative to the axis of rotation;
• geometry of the ABS toothed rotor disturbed;
• ABS harness fault, speed sensor fault.

Remedies:

• tighten the sensor mounting bolt to a torque of 7–10 N·m (0.7–1.0 kgf·m), the ABS toothed rotor must not touch the sensor when rotating;
• adjust the hub bearing preload;
• replace the worn hub bearing or replace the hub assembly with bearing and rotor;
• rectify the ABS harness fault or replace the ABS harness;
• replace the speed sensor.

4060 — Fault in the discharge valve circuit of the front left wheel:

Remedies: replace the ABS hydraulic unit.

4065 — Fault in the isolation valve circuit of the front left wheel:

Remedies: replace the ABS hydraulic unit.

4070 — Fault in the discharge valve circuit of the front right wheel:

Remedies: replace the ABS hydraulic unit.

4075 — Fault in the isolation valve circuit of the front right wheel:

Remedies: replace the ABS hydraulic unit.

4080 — Fault in the discharge valve circuit of the rear left wheel:

Remedies: replace the ABS hydraulic unit.

4085 — Fault in the isolation valve circuit of the rear left wheel:

Remedies: replace the ABS hydraulic unit.

4090 — Fault in the discharge valve circuit of the rear right wheel:

Remedies: replace the ABS hydraulic unit.

4095 — Fault in the isolation valve circuit of the rear right wheel:

Remedies: replace the ABS hydraulic unit.

4110 — Fault in the pump motor supply circuit:

• blown 40 A fuse in fuse box F41;
• no electrical contact of wire 22 with the vehicle body (the terminal of wire 22 is secured to the right cab side-member reinforcement);
• break in wire 14 and/or 16 and/or 17 in the ABS power harness;
• break in wire 19 and/or 20 and/or 21 in the ABS harness;
• ABS hydraulic unit fault.

Remedies:

• replace the fuse in fuse box F41;
• ensure electrical contact of wire 22 with the vehicle body;
• rectify the ABS power harness fault or replace the ABS power harness;
• rectify the ABS harness fault or replace the ABS harness;
• replace the hydraulic unit.

4121 — Fault in the valve supply circuit:

• blown 25 A fuse in fuse box F41;
• no electrical contact of wire 22 with the vehicle body (the terminal of wire 22 is secured to the right cab side-member reinforcement);
• break in wire 14 and/or 15 and/or 16 in the ABS power harness;
• break in wire 18 and/or 20 and/or 21 in the ABS harness;
• ABS hydraulic unit fault.

Remedies:

• replace the fuse in fuse box F41;
• ensure electrical contact of wire 15 with the vehicle body;
• rectify the ABS power harness fault or replace the ABS power harness;
• rectify the ABS harness fault or replace the ABS harness;
• replace the hydraulic unit.

4161 — Break in the wire from the hydraulic unit to the brake light switch:

• fault in the brake switch circuit of harness 99;
• break in wire 11 in the ABS harness;
• brake switch fault.

Remedies:

• rectify the harness 99 fault or replace harness 99;
• rectify the ABS harness fault or replace the ABS harness;
• replace the brake switch.

4245 — Incorrect wheel speed sensor signal:

• break in any three groups of wires 1 and 2, 3 and 4, 5 and 6, 7 and 8 to the sensors in the ABS harness;
• break in wires 3 and 4, as well as 7 and 8 in the ABS harness;
• fault of any three ABS sensors or of the rear axle ABS sensors;
• wheel diameter discrepancy of more than 6 %.

Remedies:

• rectify the ABS harness fault or replace the ABS harness;
• replace the ABS sensors;
• fit tyres in accordance with the requirements for this vehicle, set the tyre pressure in accordance with the requirements for this vehicle.

4550 — Hydraulic unit ECU fault:

• fault of the ABS hydraulic unit control unit;
• low on-board network voltage. The voltage between contacts 32 and 13, 38 of the hydraulic unit control unit is less than 9.3 V.

Remedies:

• replace the ABS hydraulic unit;
• rectify the faults associated with low supply voltage in the vehicle's on-board network;
• rectify the harness 99 fault or replace harness 99;
• rectify the ABS harness fault or replace the ABS harness.

4551 — Coding variant error:

• coding variant absent (hydraulic unit in as-delivered condition).

Remedies: set the coding variant in accordance with the model of this vehicle.

4800 — High on-board network voltage:

• voltage between contacts of the hydraulic unit control unit No. 1, 25, 32 and 13, 38 of more than 17.4 V.

Remedies: rectify the faults associated with high supply voltage in the vehicle's on-board network.

4287* — Acceleration sensor fault — incorrect signal:

• acceleration sensor not secured;
• acceleration sensor fault.

Remedies:

• check and, if necessary, tighten the bolts securing the acceleration sensor bracket and securing the acceleration sensor to the bracket to a torque of 5.5–8.0 N·m (0.55–0.8 kgf·m);
• replace the acceleration sensor.

4287* — Acceleration sensor fault — line error:

• break in wire 27 and/or 28 and/or 29 and/or 30 and/or 31 and/or 32 in the ABS harness and/or in harness 154;
• short circuit of wire 28 and/or 31 to the negative or positive battery terminal;
• sensor not connected to harness 154;
• ABS harness 154 not connected to the ABS harness;
• sensor fault.

Remedies:

• rectify the harness 154 fault or replace ABS harness 154;
• rectify the ABS harness fault or replace the ABS harness;
• connect the acceleration sensor to harness 154;
• connect harness 154 to the ABS harness;
• replace the acceleration sensor.

* — only for a vehicle with 4×4 wheel arrangement.

Bleeding the brakes with ABS installed

Using the «Hydraulic unit bleeding» subsection, air is removed and the internal circuits of the hydraulic unit are filled with brake fluid.

Important: hydraulic unit bleeding is required only after installing a new hydraulic unit.

The manufacturer of the «Bosch» hydraulic unit notes the need to use a bleeding device that creates an excess pressure of 2 bar (~2 kgf/cm²) in the brake fluid reservoir.

Important: before bleeding the hydraulic unit, the brake system must be bled in the usual way.

Hydraulic unit bleeding is carried out in 4 stages in the following mandatory sequence:

• bleeding of the rear left wheel;
• bleeding of the front left wheel;
• bleeding of the front right wheel;
• bleeding of the rear right wheel.

During bleeding, the vehicle brake pedal must be pressed and released at a rate of one press/release approximately every four seconds, while monitoring the brake fluid level in the master cylinder reservoir so that the bottom does not run dry.

Important: hydraulic unit bleeding is carried out only with the engine not running.

During bleeding, the battery must be fully charged (the voltage between the hydraulic unit contacts 13, 38 and 1, 25, 32 must be in the range 12–13.5 V).

During hydraulic unit bleeding, a tube must be fitted to the bleed valve, with the other end of the tube placed in a container of brake fluid; the bleed valve of the relevant wheel must be opened and the brake pedal pressed.

To start bleeding, the bleeding stages must be selected in the following sequence:

• bleeding of the rear left wheel;
• bleeding of the front left wheel;
• bleeding of the front right wheel;
• bleeding of the rear right wheel.

After selecting the bleeding stage, press the «Enter» key. A message according to figure 16 will appear on the display.

To start the bleeding procedure, press the «F2» key.

Then open the bleed valve of the relevant wheel and press the brake pedal at a rate of one press/release approximately every four seconds.

If bleeding is completed successfully, a message according to figure 17 is displayed.

Then, in accordance with the message displayed on the tester-scanner screen, bleeding must be continued in the usual way until the air is removed from the hydraulic system (see the «Brakes» section, «Filling (bleeding) of the brake system» subsection).

At the end of bleeding of this wheel, press the «Esc» key.

A message according to figure 18 will appear on the tester-scanner screen.

If the test is not completed successfully, the message according to figure 17 is not displayed. In this case, repeat the bleeding procedure of the relevant wheel. Then, if necessary, check the ABS faults and rectify them.

The remaining bleeding stages must be carried out in the same way.

If all bleeding stages are completed successfully and in the correct sequence (first the rear left wheel, then the front left, then the front right and the rear right), a message according to figure 19 is displayed. In this case, in the «Parameters» section, the status of the «Filling» parameter changes from «stat» to OK.

Subsection «Tests»

The «Tests» subsection consists of two items: checking the correct connection of the pipes and the operability of the hydraulic unit valves; checking the speed sensors.

The test «Checking the correct connection of the pipes and the operability of the hydraulic unit valves» consists of 4 stages:

• checking the front left channel;
• checking the front right channel;
• checking the rear left channel;
• checking the rear right channel.

This test is carried out on a two-axle or single-axle brake tester with running rollers. The roller speed must be in the range from 2.5 to 10 km/h.

Before carrying out this test, the axle of the vehicle to be checked must be placed on the brake tester, the tester switched on and braking applied for the whole duration of the test (the pedal is released only after the test of the selected channel).

Checking one of the wheels of the axle being tested is activated by pressing the «Enter» key.

Then follow the instructions displayed on the tester screen in accordance with fig. 21.

During this test, a temporary reduction in braking force on the selected wheel must occur, which confirms the correct connection of the pipes and the operability of the valves.

The test of the other channels is carried out in the same way.

The test «Checking the speed sensors» allows the quality of the speed sensor signals to be checked.

This test is carried out on a two-axle or single-axle brake tester with running rollers at a constant roller speed in the range from 2.5 to 10 km/h.

Before carrying out this test, the axle of the vehicle to be checked must be placed on the brake tester and the tester switched on.

Then select the test and activate it by pressing the «F2» key. On the display, in the «state» line, the current state of the test will be shown.

The «Execution» state of the test is shown in fig. 22.

At the end of the test, the minimum and maximum speeds measured by the speed sensors of the wheels being checked will be displayed.

All measured speed values are viewed using the ▼ and ▲ keys.

Important: the difference between the maximum and minimum speed values obtained from the wheel speed sensor on the scanner-tester display must not exceed 10 % of the roller speed of the tester.

The test of the speed sensors of the other axle, when using a single-axle tester, is carried out in the same way.

Removal and installation of the ABS hydraulic unit

To remove the hydraulic unit it is necessary:

• to disconnect connector 3 (fig. 23) of the ABS harness wires from the plug connector of the electronic control unit of the hydraulic unit;
• to disconnect six pipes from the hydraulic unit;
• to plug the openings in the hydraulic unit with plugs;
• to slacken the two nuts 2 securing the hydraulic unit to the bracket and withdraw the hydraulic unit.

When installing it is necessary:

• to install rubber bush 3 for the lower mounting of the hydraulic unit in the oval opening of the hydraulic unit bracket;
• to install hydraulic unit 1 in bracket 4;
• to carefully connect and tighten the six connecting nuts 1 (fig. 24) securing the pipes to the hydraulic unit to a torque of 14–16 N·m (1.4–1.6 kgf·m).

Important: the nuts have different threads. Changing the connection points is not permitted.

• to tighten the two nuts 2 securing the hydraulic unit to the bracket to a torque of 8–9 N·m (0.8–0.9 kgf·m);
• to check the identification number of the ABS control unit software using a special diagnostic program, to install the ABS harness wire connector in the plug connector of the electronic control unit of the hydraulic unit, to top up the brake fluid in the reservoir and to bleed the brake system and the hydraulic unit.