ABS/TCS System Description

ACCELERATION SLIP REGULATION (ASR) SYSTEM

Available-Traction Utilization: Traction utilization is a function of tire design, tire inflation pressure, tire load, tire slip angle, level of percent slip, and road condition.

The Acceleration Slip Regulation (ASR) system uses engine spark retard, throttle close-down and rear brake intervention to provide enhanced acceleration and vehicle stability. ASR provides well-balanced performance over a variety of road conditions. The ASR system is capable of functioning up to maximum vehicle speed. The system enhances the following general vehicle characteristics: Directional control,traction, and maneuverability.

The ASR system accomplishes these goals through use of wheel speed information, as well as the following:

^ Vehicle speed, to give traction priority at low speeds and directional control priority at high speeds.
^ The speed difference of the non-driven (front) wheels, to detect a cornering maneuver. Directional control has priority when cornering.
^ Vehicle acceleration and throttle position. In situations of low vehicle acceleration the control strategy is more sensitive.
^ Brake applied input.

The ASR system functionally integrates three subsystems by the following methods:

^ Spark retard.
^ Throttle close down.
^ Rear brake intervention.

The system is capable of simultaneous or separate usage of engine control and rear brake intervention. When an ASR event occurs, the ASR system disables cruise control and, if equipped with automatic transmission, the torque converter clutch. The cruise control disable function uses a relay, located near the steering column on the left side of the instrument panel.

Wheel slip regulation logic uses a reference velocity derived from the non-driven (front) wheels. A sophisticated slip threshold calculation considers vehicle acceleration, vehicle speed, cornering and start-up. There are wheel acceleration rates whereby rear brake intervention will be used to reduce wheel spin. The following items are specific to the ASR portion of the ABS/ASR system:

^ Adjuster assembly - Throttle and cruise control cables - DC motor, and cam assembly.
^ Prime pipe from master cylinder to BPM valve.
^ ASR "OFF" switch.
^ Spark retard table added to the PCM/ECM.
^ Throttle Position (TP) sensor module.
^ Cruise control, cutoff relay.
^ "ASR ACTIVE," "SERVICE ASR" and "ASR OFF" lamps.
^ Lateral accelerometer.

Common ABS/ASR Components:

^ Four wheel speed sensors and toothed sensor rings.
^ Master cylinder reservoir supplying the ABS/ASR BPM valve.
^ BPM valve.
^ Electronic Brake and Traction Control Module (EBTCM).
^ Wire harness.

Engine Torque Control
Engine torque can be controlled with one or more devices which affect air, fuel and spark firing angle, the most effective being air restriction. A cable extension mechanism called the "Adjuster Assembly" closes the throttle during control modes, provides the driver with pedal feedback during adverse road conditions, and reduces engine torque. Fast engine torque reductions using an optimized method of spark retard can be used to increase driver comfort and vehicle stability.

Rear Brake Intervention
Brake application is a relatively slow and less effective method of engine control than spark retard and/or throttle close-down. However, brake application is effective at slower speeds during excess wheel spinning. With individual rear brake control, it is possible to utilize the traction available on split- coefficient road conditions (such as dry and wet, wet and icy, etc.) and improve acceleration.

Brake intervention occurs only below vehicle speeds of 80 km/h (50 mph). Above 80 km/h (50 mph), engine torque control results only from spark retard and throttle close-down.

ASR System "OFF"
The ASR system can be turned "OFF" by pressing the "ASR OFF" switch located just above the headlamp switch assembly in the instrument panel. Refer to "ASR OFF Switch" in this section for additional information.

Tires and ABS/ASR Spare Tire
Using the compact spare supplied with the vehicle will not affect the performance of the ABS/ASR system.

Replacement Tires
Tire size is important for proper performance of the ABS/ASR system. Replacement tires should be the same size load range and construction as the original tires. Replace tires in axle sets and only with tires of the same TPC (Tire Performance Criteria) specification number. Use of any other tire size or type may seriously affect the ABS/ASR system operation. For more information on original equipment and replacement tires.

Warning/Indicator Lamp Operation
There are five status indicator lamps used with the ABS/ASR system. They are all amber and are located in the DIC.

^ "ASR OFF" - indicates ASR system has been turned "OFF."
^ "ASR ACTIVE" - indicates the ASR system is currently influencing rear wheel acceleration slip.
^ "ABS ACTIVE" - indicates the ABS system is currently in a wheel-lock control condition.
^ "SERVICE ABS" - indicates a condition present in the ABS system which requires service.
^ "SERVICE ASR" - indicates a condition present in the ASR system which requires service.

The red "BRAKE" warning lamp is also connected to the fluid level warning switch, which affects ABS/ASR system operation. Refer to "Fluid Level Warning Switch."