Summary
ABS, EBD and TRACSSummary
Control module
The control module has two different microprocessors which receive signals from the different sensors in the car. The microprocessors work in parallel, using a program which operates the ABS, EBD and TRACS systems.
The control module for ABS, EBD and TRACS is integrated with the hydraulic unit and is located in the engine compartment.
The main function of the control module is to process signals from the different sensors and control the hydraulic pump and the electromagnetic hydraulic valves (inlet and outlet valves) in the hydraulic unit when using ABS, EBD or TRACS. The control module houses the electrical coils for the inlet and outlet valves.
The control module checks its calculations and all input and output signals via the built-in diagnostics functions. If the control module detects a fault, ABS, EBD or TRACS will be switched off completely or disabled, depending on how serious the fault is, and the ABS (TRACS) light will come on. When disconnecting, the control module aborts or stops all functions (not road speed signal); disabling prevents certain functions from being performed.
Any faults will be recorded in the control module memory. Data can be read out using the Volvo ST connected to the DLC in the passenger compartment in front of the gear lever.
When the car is driven off, the control module checks that it is receiving signals from the wheel sensors. When the car first reaches 20 km/h (12.5 mph) (or 40 km/h (25 mph) if the brake light switch is activated), the control module checks the pump engine by activating it briefly. This means the hydraulic pump will be audible. This is completely normal.
ABS is not activated until the car's road speed exceeds approx. 7 km/h (4.4 mph).
Input signals
The control module receives input signals on the car's operating conditions from the following components:
Wheel rotation speed, acceleration and retardation from wheel sensor and pulse wheel. (1, 2)
Signal from EBD pressure sensor when the primary circuit is pressurized. (3)
Signal from brake light switch when the driver depresses the brake pedal. (5)
And in cars with TRACS:
When TRACS cuts in or out from the switch on the instrument panel (dashboard). (9)
The following are needed for the control module to function:
Voltage supply, 30-supply, from the battery. (6)
Voltage supply, 15I-supply, from the ignition switch.(7)
Ground connections.
Control functions
Based on Input signals, the control module controls the following functions and components:
ABS warning light on the instrument panel (dash- board).
The hydraulic unit hydraulic pump and the inlet and outlet valves. (4)
ABS and EBD systems
And in cars with TRACS:
TRACS system.
TRACS warning light on the instrument panel for faults which only affect the TRACS system and when the TRACS function is disabled using the switch.
Other output signals
The control module sends a speed signal to the instrument panel (dashboard) based on the input signals.
The road speed signal is the average of the front wheel speeds.