Traction Control Module: Description and Operation
There are four different versions of the ABS/ASR control unit. This reflects the different performance maps for the electronic accelerator system.
There are two versions with speed sensor output and two without. This model uses on of the units without speed signal output.
Control Unit Connector:
To prevent mistaken interchange of the different ABS/ASR control units for the different vehicle/engine combinations, there are two lugs cast on the sides of the control unit connector; and at the front clasp there is a notch, located in different positions for the different vehicle/engine combinations.
Control Unit Connector:
On the ABS/ASR control unit there are two notches (arrows) cast on the sides of the connector guide. In the catch on the right side there is a web (arrow) in different positions depending on the vehicle/engine combination. The control unit consists of separate printed circuits equipped with electronic components. The connection with the wiring harness uses a 35-pole connector.
Besides the ABS functions, the ABS/ASR control unit contains all the ASR functions. it is functionally divided as follows:
^ Signal conditioning,
^ Input amplifiers,
^ Logic components,
^ Safety circuits,
^ Output drivers.
SIGNAL CONDITIONING
The signal conditioning components convert the input signals from the four wheel speed sensors (from the original sine-wave AC to a digital square wave) and send them for processing to the ASR and ABS microcomputers.
INPUT AMPLIFIERS
There is an input amplifier for each of the inputs from the:
^ Stop lamp switch,
^ Throttle valve actual position signal,
^ Snow chain switch,
^ Pressure switch.
The input amplifiers filter the incoming digital signals and convert them into levels usable by the logic components and the safety circuit.
LOGIC COMPONENTS
The logic components of the ABS microcomputers and the ASR microcomputers process all the input signals.
WHEEL SPEED SIGNALS:
The conditioned wheel speed signals are continuously compared and then with the prescribed spin thresholds (depending on speed differences between rear and front wheels and on the vehicle speed).
This comparison calculates the following factors:
^ Drive wheel spin,
^ Acceleration and deceleration,
^ Average front wheel speed,
^ Identification of turns.
If the calculated factors exceed specific thresholds, then ASR control operation begins. The throttle valve output signal controls the position of the throttle valve.
BRAKE LAMP SWITCH SIGNAL:
If the brake pedal is moved, the switch sends a signal to the logic components, which de-energize the solenoid valves. ASR control operation stops immediately.
THROTTLE VALVE ACTUAL POSITION SIGNAL:
During ASR operation the logic components control how much the throttle is closed, using the throttle valve actual verses nominal position signals.
SNOW CHAIN SWITCH SIGNAL:
When engaged the snow chain switch sends a signal to the logic components, which raise the spin threshold. A confirmation signal is sent to the snow chain switch LED indicator.
PRESSURE SWITCH SIGNAL:
The recharge signal from the pressure switch activates the ASR charging pump and the return/pressure pump through the corresponding output from the ABS/ASR control unit.
SAFETY CIRCUIT
The purpose of the safety circuit is to identify faulty signals within the electronic control unit and malfunctions in the hydraulic unit relays as well as in the wheel speed sensors. In case of a malfunction, the ABS and ASR systems turn off.
The safety circuit also continuously monitors battery voltage. If the battery voltage falls below 10 V, the ABS/ASR systems turn off until the voltage returns to the specified level. The following malfunctions are recognized:
^ Defective ABS/ASR control unit,
^ Defective solenoid valve,
^ Defective wheel speed sensor or intermittent open circuit,
^ Defective relay,
^ Defective return/pressure pumps,
^ Leaking pressure reservoir,
^ Defective pressure switch.
If the warning lamp lights, that indicates a malfunction has been detected. If the ignition is turned off, briefly occurring malfunctions are erased from memory again.
OUTPUT DRIVERS
The output signals from the ABS and the ASR microcomputers to the solenoid valves, relays, warning lamps, etc. are amplified by large-signal transistors.