Design

Design

Control module and ABS hydraulic modulator
The ABS control module is mounted on the hydraulic modulator in the engine compartment.
It is supplied with power via two fuses and connected to ground by a ground terminal.
There are diagnostics for the valve coils.
There are three different versions of the ABS control module.
The ABS control module does not support software downloading. The control modules are supplied with the correct software installed.





ABS control module
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.





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.





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.





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.

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.

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.

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.

Stop (brake) lamp switch




The stop (brake) lamp switch is a single pole switch positioned at the brake pedal lever. It self-adjusts during its installation.
The stop (brake) lamp switch transmits signals informing the control module that braking has started. The control module interrupts any traction control and goes to standby mode for ABS / EBD control, which means that the control module can make more accurate calculations. If the control module does not receive a signal from the stop (brake) lamp switch, there is still ABS control available but the control is more vigorous at the start of the ABS control.
The stop (brake) lamp switch is supplied with power from the battery. When the switch closes, the stop (brake) lamp lights and the control module receives a signal that braking is occurring.
In All-wheel drive (AWD) cars equipped with TRACS, the stop (brake) lamp switch has two switches to ensure that traction control stops when braking. If a fault occurs in the stop lamp switch signal the traction control in the TRACS function is reduced from operating on all the wheels to operating on the front wheels only.
There are diagnostics for the stop (brake) lamp switch.

Yaw rate sensor (Only DSTC)




The two yaw rate sensors are in the passenger compartment. One is positioned in the center console under the storage compartment and the other under the right-hand front seat. The gyro element sensors provide information about the yaw rate speed of the vehicle (lateral speed) and are used to calculate the stability functions in the ABS control module. The information is transmitted via analog signals (0-5 V), where approximately 2.5 V is the normal value when traveling straight ahead. An in-built filter filters the signal so that no interference from high frequencies occur and so that vibrations in the car body do not affect the different calculations in the control module.
The two sensors are installed in opposite directions. The only reason for two sensors is for safety. They measure the same angle and provide a combined average.
The sensors are piezoelectric. There are diagnostics for the sensors.

Lateral acceleration sensor (Only DSTC)




The lateral acceleration sensor is positioned on the same bracket as one of the yaw rate speed sensors in the center console under the storage compartment.
The information from the lateral acceleration sensor is used to calculate the stability functions in the ABS control module. Analog signals are used (0-5 V), where 2.5 V corresponds to no acceleration, voltage lower than 2.5 V corresponds to acceleration to the right and voltage greater than 2.5 V acceleration to the left. An in-built filter filters the signal so that no interference from high frequencies occur and so that vibrations in the car body do not affect the different calculations in the control module.
The sensor is of the capacitance type. There are diagnostics for the sensor.
When replacing the side acceleration sensor the ABS control module must be calibrated according to the information in VIDA vehicle communication or manually via a test drive.

Active power brake booster, pedal pressure sensor (DSTC only)




The power brake booster is positioned on the firewall in the engine compartment. It consists of a vacuum cylinder (1), pedal position sensor (2), pressure build-up valve (3) and pedal pressure sensor (4).
The pedal pressure sensor is positioned in the power brake booster and provides the ABS control module with information about brake activity by the driver. If the driver depresses the brake pedal during traction control the control will stop.
The active power brake booster is controlled by the ABS control module and builds-up an initial brake pressure. This is so to allow braking during DSTC control. Initial brake pressure is built up within 100 ms of control starting. This occurs without the driver needing to depress the brake by opening the pressure build-up valve and allowing atmospheric pressure to enter the rear chamber. The brake pressure sensors (5) continuously monitor the brake pressure. The pulse width controlled pressure build up valve in the power brake booster maintains the pressure during DSTC control at around 10 bar.

Pedal position sensor




The pedal position sensor is mounted on the power brake booster in the engine compartment. The sensor, which responds to the push rod for the pedal, is a sliding potentiometer. 0 mm corresponds to 0 V and 38.5 mm movement corresponds to approximately 95 % of battery voltage (Ubat).
The pedal position sensor signal is used to check the function of the stop (brake) lamp switch.
The pedal position sensor is directly connected to the engine control module (ECM). This pedal position sensor has no ABS function.

Brake pressure sensor (Only DSTC)




Two brake pressure sensors are positioned on the master cylinder. One sensor is located on the primary circuit and one on the secondary circuit. The information is transmitted via two analog signals (measurement range 0-5 V) and is used by the ABS control module to calculate the brake pressure during DSTC control, and when the driver applies the brakes.
The sensors receive voltage via the ABS control module. There are diagnostics for the sensors.
When replacing the brake pressure sensor the ABS control module must be calibrated according to the information in VIDA vehicle communication or manually via a test drive.