The control module contains two different micro-processors which receive signals from different sensors in the system. The micro-processors operate in parallel and use a program to compute the necessary ABS and electronic brake force distribution functions. The ABS control module has eight valve coils for the hydraulic valves, four outlet valves and four inlet valves.

The control module has two connectors, one for the car wiring and one for the hydraulic pump.

Scheme 141

ABS control module with TRACS (traction control system) / STC (stability and traction control)

The control module for ABS with TRACS/STC also contains two micro-processors and the four outlet valves and four inlet valves used in the standard ABS control module. The difference (software aside) is that the control module has two extra valves. One valve (Separation Valve-SV) separates the master cylinder from the brake circuit. The other valve (Hydraulic Shuttle Valve-HSV) opens the connection to the brake fluid reservoir during traction control.

Scheme 142

ABS control module with DSTC (dynamic stability and traction control)

The ABS control module with DSTC has twelve valve coils for the hydraulic valves, of which four are outlet valve coils, four are inlet valve coils, two are used for traction control and two more are for DSTC. When replacing the ABS control module in a car with DSTC, the control module must be calibrated according to the instructions for VIDA vehicle communication or manually via a test drive.

Configuring the control module

From model year 2000 the ABS control module with DSTC is factory programmed with software for several models. The central electronic module (CEM) provides information about the car configuration on the Controller area network (CAN) in the car. The ABS control module for DSTC reads the information and uses it for configuration during the first ignition cycle.

Scheme 143

ABS hydraulic modulator

The ABS hydraulic modulator is located in the engine compartment.

The ABS hydraulic modulator consists of a pump motor and the hydraulic valves which control the pressure to the different hydraulic brake circuits. During ABS control these valves limit the brake pressure to each wheel individually to prevent the wheels from locking. If necessary the valves operate with the hydraulic pump. During stability and traction control the pump and valves combine to supply brake pressure.

There are diagnostics for the pump motor.

Note. The illustration shows the hydraulic modulator for ABS and ABS with TRACS/STC. The hydraulic modulator for ABS with DSTC looks slightly different. The pump motor connector is integrated in the ABS hydraulic modulator.

Scheme 144

Scheme 144: STC/DSTC switch

The switch for STC/DSTC is positioned next to the other buttons on the lower section of the climate control module (CCM). The stability and traction control function can be switched off manually. When the ignition is switched on all functions are engaged. The switches have a green LED indicator which display the ON-position.

Note. The illustration displays the switch for cars equipped with STC.

Scheme 145

Scheme 145: Warning lamps

The brake system uses three warning lamps positioned in the combined instrument panel.

ABS warning lamp

The ABS warning lamp indicates an ABS system fault.

When the ignition is switched on, the ABS control module check the function of the ABS warning lamp. The lamp lights for up to 5 seconds. The ABS control module continuously monitors the system voltage. If the voltage increases or decreases beyond certain parameters the ABS warning lamp lights up and the system goes into standby mode. The lamp goes out when the correct operating system voltage is returned. No diagnostic trouble codes (DTCs) are stored for defective voltage.

Brake warning lamp

The brake warning lamp indicates

faults in the electronic brake force distribution (EBD) function
that the brake fluid level is too low.

Traction control warning lamp (only cars with STC/DSTC)

The traction control warning lamp is on continuously when

STC/DSTC is deactivated because a diagnostic trouble code (DTC) is stored
STC/DSTC is manually switched off
the brake disc temperature is too high.

The traction control warning lamp flashes when

a drive wheel starts to spin during acceleration. The control module is activated to regain traction
the lateral stability limit is exceeded (the car oversteers or understeers) during active yaw control.

Scheme 146

Scheme 146: Wheel sensors

There are four wheel sensors, one at each wheel. The wheel sensors supply the control module with information about the rotation speed, acceleration and retardation of each wheel. By recording the pulses, the control module can calculate the wheel speed.

The wheel sensors are active sensors. When the pulse wheel rotates, the sensor generates a pulsed current (quadratic wave) where the strength of the current depends on the position of the pulse wheel. The signals from the coils in the wheel sensors are then affected by a magnetic resistance element, which generates a current which changes between 7mA and 14mA, and whose frequency increases with speed.

On the front wheels, the pulse wheel is pressed onto the outer constant velocity joint and the wheel sensors are located radially in the shaft housing relative to the pulse wheel. On the rear wheels, the pulse wheel is pressed onto the hub and the wheel sensors are located axially relative to the pulse wheel. The rear pulse wheels can be replaced. Both the front and rear pulse wheels have 48 teeth. In the event of a fault in any of the wheel sensors the following functions do not engage

ABS
TRACS
STC
DSTC.

Electronic brake force distribution (EBD) is available if one wheel sensor is faulty. Electronic brake force distribution (EBD) is disengaged if there is a fault in more than one wheel sensor simultaneously.

The control module calculates the vehicle speed using the signals from the wheel sensors.

There are diagnostics for the wheel sensors.

Control module and ABS hydraulic modulator Volvo V70 II