The vehicles can be equipped with a 4-channel anti-lock braking system (ABS) of type 4S / 4M brakes (4 sensors / 4 modulators) with a microprocessor control unit f. Wabco (Germany) or BPO Ekran (Belarus)

The main purpose of the system is to automatically maintain optimal braking of the car without blocking (skidding) the wheels, regardless of whether the road is slippery or dry.

Thanks to this, cars acquire a number of advantages:

  • - increase active safety by providing stability and controllability during braking and increase the braking efficiency of the car, especially on wet and slippery roads;
  • - tire life extension;
  • —the ability to increase the average safe speed of movement.

In addition, the applied ABS design f. Wabco can provide a speed limiting mode, and ABS BPO "EKRAN" provides storage and output of information about the effectiveness (average deceleration) of the last braking of the car and the pre-emergency modes of the system for the last 40 seconds.

Location of MAZ ABS elements

The location of the system elements on the vehicle chassis is shown in fig. 1.

The system contains inductive wheel speed sensors 1, electro-pneumatic brake pressure modulators 2 installed in the brake lines in front of the brake chambers of the rear and front wheels, an electronic unit 3 mounted on a switching board 4 installed under the bunk behind the passenger seat, relay 5 and a box of 6 fuses.

The diagnostic connector 11 and buttons 12 and 13 for calling the ABS diagnostic mode of the tractor and trailer are located under the right cover of the instrument panel (Fig. 2).

Location of indicator lamps and MAZ ABS elements

Indicator lamps 1, 2, 3 and 4 and switches 5, 6 of the ABS operation modes are installed on the main and additional dashboard of the instrument panel (Fig. 2).

Control lamps 1 and 2 (red) with the ABS symbol indicate the serviceability / malfunction of the ABS of the tractor or trailer, lamp 4 (ASR / INF) - serves as a means of displaying information about wheel slip, as well as the type and location of a malfunction in the system in diagnostic mode.

When ABS BPO "Ekran" is installed on the specified lamp, information about the braking efficiency is also displayed.

Switch 5 is designed to switch the ABS to a special mode of operation when the car is braking in mountainous areas (for example, when descending a mountain) on a road covered with gravel or loose snow.

Switch 6 is used when the Temposet (speed limit) mode is enabled.

On the rear beam of the cabin support there is a socket 12 for connecting the cable 10 of the trailer ABS power supply and a parking socket 13 (Fig. 1).

The location of ABS elements and electronic units on the switching board is shown in fig. 3 and 4.

Electrical connection diagram of ABS elements BPO Ekran and ABS f. Wabco is shown respectively in fig. 5 and 6.

Location of ABS elements and Ekran electronic unit on the switching board.

Fig. 3. Arrangement of ABS elements and Ekran electronic unit on the switching board

Location of ABS and Wabco electronics on the breakout board

Fig. 4. Location of ABS elements and electronic unit f. Wabco on the breakout board

Fig. 5. Electrical circuit diagram of ABS BPO "Ekran"

Fig. 6. Electrical circuit diagram ABS f. Wabco

System operation

When the power is turned on (when the starter lock key is turned to the In the “instruments” category, control lamps with the ABS ASR / INF symbol are turned on (Fig. 2) and the test control of the electronic unit and electrical circuits of sensors, modulators and switching devices takes place.

When the system is working properly, the ASR/INF lamp goes out 2-3 seconds after turning on the power, and the lamp with the ABS symbol of the tractor goes out when the vehicle starts moving when the vehicle reaches a speed of 5-7 km/h.

If a malfunction occurs in the system or the electrical circuits of one of the elements (sensors, modulators, etc.) or control circuits, the red indicator lamp with the ABS symbol lights up.

This turns off the power to the corresponding circuits (modulators) and the brake system or non-adjustable ABS circuit of the brake system works as usual (from the brake valve),

The system does not require special maintenance, except for a functional check and checking the installation of ABS sensors when adjusting or replacing bearings in wheel assemblies or changing brake linings (if the hubs were removed).

Installation of the ABS sensor in the wheel assembly of the front axle MAZ

For normal operation of the ABS, the gap (see Fig. 7 and 8) between the stator and the rotor of the sensor should not exceed 1.3 mm.

Installing the ABS sensor in the MAZ rear axle wheel assembly

For normal operation of the ABS, the gap between the stator and the rotor of the sensor should not exceed 1.3 mm

To set the minimum working gap between the stator and the rotor, it is necessary, the sensor stator, acting on its end with a force of 120-140 N (12 - 44 kgf) or lightly tapping with a non-metallic object (in the wheel assembly of the rear axle through a special hole in the caliper and a plug in the brake shield), move in the clamping sleeve in the axial direction until it stops against the rotor ring, and turn the wheel hub 2-3 turns.

If the red lamp with the ABS symbol does not go out at a speed above 7-10 km / h, you should check the installation of sensors in the wheel assemblies, diagnose the system using flashing codes, re-check the system with an analysis of possible malfunctions according to the table, or contact to a service station for troubleshooting.

Control check of the system

The control check consists of three stages: preliminary check, check of operating modes and check of diagnostic mode.

1. Preview

  • 1.1. By external inspection, make sure that the cable devices, connectors of the electronic control unit, modulators, sensors, as well as relays and fuses and ABS warning lamps are connected.
  • 1.2. Turn on the button of the remote switch "mass". Turn the starter lock to the "instruments" position. At the same time, the control lamps with the ABS and ASR / INF symbols light up and the pilot valves of the modulators should work (detected by ear) for a short time.

If the electrical part of the system is working properly, the ASR / INF indicator lamp should go out after 2-3 seconds.

  • 1.3. Start the engine and bring the pressure in the circuits to normal (6.9-8.2 kg/cm2). Press the brake pedal. In this case, the brake mechanisms should work, there should be no air leaks from the system.
  • 1.4. Start moving. At speeds above 7 km/h, the red warning light with the ABS symbol of the tractor must go out (if the vehicle is hitched to a trailer, the warning light with the ABS symbol of the trailer must also go out).

2. Checking ABS operating modes

2.1. Main Mode

Checking the main mode of ABS operation is carried out with switch 5 (Fig. 2) in the initial (not pressed) state. In this case, it is necessary to accelerate the car to a speed of 35-45 km/h and make a sharp deceleration on a surface with a high (asphalt) and low coefficient of adhesion (wet asphalt concrete, snow, ice).

The wheels must not block at the same time (only short-term blocking is allowed at speeds below 15 km / h), the car must decelerate with the prescribed efficiency (on dry pavement i = 5 m / s2) and the characteristic sound of the operation of brake pressure modulators must be heard in the mode of cyclic discharge of compressed air from the brake chambers.

Indicator lamp 1 with the ABS symbol should light up when the starter switch is turned on again to the “instruments” position.

Special Mode Check

Checking the special mode of ABS operation is carried out in the same way when switch 5 is on (pressed) (Fig. 2).

In this case, the red control lamp 1 should work in a flashing mode, and the ABS system in a lower frequency mode.

Check re "Temposet" speed limiter.

The mode is activated when the vehicle speed is at least 25 km/h. to do this, when the set speed is reached, press switch 6 (Fig. 2) with the “TSET” symbol. In this case, the lamp should light up with the ASR / INF symbol.

When driving at a speed lower than the speed at which the Temposet mode was activated, the ASR/INF lamp is off.

Check diagnostic mode

Checking the operation of the system in diagnostic mode is carried out in three stages:

  • 3.1. When the starter switch is turned on from the off state to the “instruments” position. At the same time, the red control lamp with the ABS symbol lights up, the solenoid pilot valves of the modulators should work (for a short time) (determined by ear).
  • 3.2. At the start of the movement. At vehicle speeds above 7-10 km/h, the red warning light with the ABS symbol must go out.
  • 3.3. When you press the diagnostic button 12 (Fig. 2), the lamp with the ASR / INF symbol should give out a flashing light code, as described below.


  • 1. The special mode of operation of the ABS is activated only for the time of checking or driving in mountainous areas. After that, the specified mode (switch 3) should be turned off.
  • 2. When carrying out repairs and troubleshooting, you must stop the engine and turn off the power to the system.

The power to the system is turned off when the starter and instrument switch key is turned to the “off” position and the “mass” switch is turned off.

To temporarily disable the ABS, for example, when checking the simultaneous operation of the wheel brakes and the effectiveness of "skid" braking, the FU10 fuse is removed from the socket in the fuse box (Fig. 3, 4).

3. It is strictly forbidden to carry out welding work on the car with the electronic unit installed. In this case, the electronic unit must be turned off and removed from the vehicle.

If difficulties arise in determining the malfunction, the fuses are checked (Fig. 3 and 4), control diagnostics of the system using flashing light codes, or a comprehensive check with a special diagnostic tester.

Possible malfunctions of the ABS system and solutions

Signs of problems

- Possible reason


When you turn the ignition key, the "gauges" do not light up indicator lamps with the symbols "ABS" or "ASR/INF"

- There is no or low voltage of the car network, there is no voltage of the control unit

Check the mains voltage. Check power fuses "ABS/ASR"

- Malfunction of control lamps or wiring

Replace defective lamp, check wiring

- Faulty control unit

Replace control unit

When the ignition key is turned to the gauges position, the ABS and ASR/INF warning lights come on and stay on

- Open or short circuit in the circuits of cables or connectors of sensors, modulators or PBS electro-pneumatic valves

Check with a tester the circuits of sensors, modulators and electro-pneumatic valves of the PBS, eliminate the malfunction

When driving at a speed of more than 7 km/h, the red indicator lamp with the “ABS” symbol of the tractor or trailer does not go out

- The gap between the sensor stator and the rotor has been increased

Check the voltage of the output signal of the sensors with a tester, adjust the gap

- Malfunction of the sensor coil, broken contact in the connector for connecting the sensor to the cable, cable break

Check the active resistance of sensors and cables, restore contact, replace the sensor.

- Malfunction of the modulator solenoid valve coil, broken contact in the connector, cable malfunction

Check the condition of the coils, cable and connector.

- Contact failure in the switching blocks

Restore contact

- Faulty wiring or faulty control unit

Check relay and wiring. Replace defective items.

After reaching a speed of 5-7 km/h, the control lamp with the “ABS” symbol goes out and starts flashing at a frequency of 0.5 Hz

- The ABS operating mode switch is in the “closed” state or the switch contact is shorted to ground

Check the switch.

Remove the short.

When braking, the red indicator lamp with the ABS symbol comes on, the ABS is intermittent

- Violation of the contact in the block of the switching board, the fastening of the control unit is broken

Restore to contact, fix the control unit

- The fastening is broken or the air gap of one of the wheel sensors is increased

Check the mounting of the sensors, restore the air gap

When braking, the ABS works, but one of the wheels locks up

- Violation of lubrication and jamming of the expanding fist or rollers of the brake pads

Disassemble the wheel assembly, fix the problem, relubricate.

- Weakened or broken brake shoe return spring

Replace spring

- Incorrect connection of sensors and modulators

Check the connection of sensors and modulators

When the brake pedal is depressed, air is bled from the atmospheric output of the modulator

- The sealing of the outlet diaphragm valve of the modulator is broken due to the ingress of a foreign body between the valve seat and the diaphragm

Replace or disassemble the modulator and eliminate the malfunction, followed by a leak test.

When you press the brake pedal, the yellow light with the trailer ABS symbol comes on

- The connection in the trailer ABS power connector is broken, the trailer ABS power cable is not connected or broken, the trailer ABS electronic unit is faulty or missing (the trailer is not equipped with ABS)

Check the connectors and fuses, connect a good cable and check the power circuit, control lamps and the trailer ABS unit