The system consists of a hydraulic modulator (contains solenoid valves and hydraulic accumulators), electric return pump, four wheel gauges (one on each wheel) and electronic control unit (ECU).
The purpose of the system is to prevent the wheel from locking up during heavy braking. As soon as one of the wheels is close to blocking, the system automatically disables this brake unit, and when the threat of blocking passes, it activates it again. In the event of an ABS failure, the brake system operates like a normal system without ABS.
Solenoid valves that regulate the brake fluid pressure in the working cylinders are controlled by an electronic unit that receives signals from wheel speed sensors. Sensors monitor the rotation speed of each wheel. By comparing these signals, the control unit determines which of the wheels has slowed down and is close to blocking.
The electronic control unit sends a signal to the corresponding modulator valve and the brake fluid pressure in this brake assembly decreases. The hydraulic pressure in each caliper is regulated separately.
If the wheel speed continues to decrease, the ECU turns on the return pump, which pumps the brake fluid back into the master cylinder, reducing the pressure in the brake assembly. As soon as the wheel speed returns to normal, the pump is switched off, the solenoid valve opens and the brake force is applied again. This cycle can repeat up to 10 times per second.
The operation of the solenoid valves and the return pump creates impulses in the hydraulic line. When the ABS system is functioning, these impulses are felt on the brake pedal.
On models with 6 cylinder engines, the hydraulic modulator is equipped with an additional set of solenoid valves that are part of the traction control system (TS). The system is activated at a speed of approximately 60 km/h and uses the signals provided by the wheel speed sensors. If the ECU determines that any wheel is starting to spin, the appropriate rear brake is momentarily applied.
The correct functioning of the ABS and traction control system is entirely dependent on electrical signals. To prevent the system from reacting to interference, a safety loop is built into the system that controls all impulses received by the ECU. If an abnormal signal is detected or the battery voltage is low, the systems will automatically shut down and the warning light on the instrument panel will illuminate.
Precautions
- Do not disconnect the ABS/TC electronic control harness multi-wire connector with the ignition on.
- Do not use the starting device to start the engine.
- Disconnect the multi-pin connector of the ABS/TC control unit before carrying out welding work on the vehicle.
- Do not expose the ECU to temperatures above 80°C (e.g. during painting).
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