Control Functions

Depending on the input signals, the control module controls the following components and functions:

- Solenoid hydraulic valve power supply via combination relay (1).

- Hydraulic pump motor via combination relay under ABS and TRACS control (2).

- Solenoid hydraulic valves under ABS and TRACS control (3).

- ABS warning indicator on the dashboard if there is a fault which affects ABS/TRACS (4).

- TRACS warning indicator on the dashboard, for faults which affect TRACS only. (5).

When the ignition is switched on or the engine is started, the control module switches the warning indicators on. The control module also runs an initial self-test sequence to check that it is working properly itself. The combination relay is also activated, so that the control module and the hydraulic system valves are powered.

The warning indicators go out after approx. 2 seconds if no fault is found.

At the same time, the control module activates the hydraulic valves briefly. When the hydraulic valves are activated, this shows up as slight movement of the brake pedal and noise from the hydraulic system. This is absolutely normal.

Note: This function applies only to older control module models (up to early 1994).

When the car is driven off, the control module checks that signals are coming in from the wheel sensors.

When the car reaches approx. 30 km/h (20 mph) for the first time, the control module checks that the hydraulic pump is working. It does this by activating the combination relay which in turn activates the pump motor. The rotation sensor in the hydraulic system then detects that the pump is rotating and sends a signal to the control module. Some sound from the hydraulic system will be audible temporarily. This is absolutely normal and nothing to worry about.

During this initial diagnostic routine, the control module checks continuously that all signals and components are working and that there is no internal fault in the control module itself. The ABS system is only activated once the car is travelling faster than approx. 7 km/h (4 mph).