When the EBCM detects that a wheel lock condition will occur, an ABS event begins. During an ABS event, hydraulic pressure in individual wheel circuits is controlled in order to prevent wheel lock from occurring. A separate hydraulic line and 2 solenoids are provided for each brake circuit. The ABS can hold, decrease or increase hydraulic pressure in each brake circuit. However, the ABS cannot increase the hydraulic pressure in a brake circuit above the amount which is applied to the brake pedal during braking.
An ABS event may occur at speeds equal to or greater than 13 km/h (8 mph). During an ABS event, a series of rapid pulsations will be felt in the brake pedal. These pulsations are caused by changes in the positions of the solenoid valves as the EBCM responds to input from the wheel speed sensor(s). During an ABS event on dry pavement, the tires may make intermittent chirping sounds as 10-20% wheel slip occurs. The ABS solenoids and pump motor will also make an audible sound when operating. These sounds and pedal pulsations are to be considered normal during antilock braking.
The base brake system operation during normal braking should be no different than that of previous systems. Maintaining a constant pressure on the brake pedal without causing wheel lock will provide the shortest stopping distance while still maintaining vehicle stability.
Dynamic Rear Proportioning (DRP) is a control system that is part of the EBCM programming. DRP replaces the function of the proportioning valves, present in a conventional brake system. The DRP works with the ABS to regulate the pressure to the rear brake circuit.
When the EBCM detects wheel slip, the EBCM closes the isolation valve in order to prevent additional hydraulic pressure from entering the brake circuit of the wheel(s). Pressure in the brake circuit then remains constant.
If the wheel(s) locks after the isolation valve is closed, the EBCM opens the dump valve in order to decrease hydraulic pressure in the brake circuit. The fluid which is released from the brake circuit is stored in the accumulator and is later returned to the master cylinder or the fluid reservoir by the pump.
If the EBCM detects that the speed of the wheel(s) is too great during the pressure hold or pressure decrease mode, the EBCM increases the hydraulic pressure to the brake circuit by ensuring that the dump valve is closed and then opening the isolation valve. The increased pressure comes from the master cylinder and is directly related to the pressure applied to the brake pedal.
Traction control does not have any effect on vehicle performance until the EBCM detects that the rear wheels are rotating faster than the front wheels. At this time, the EBCM requests a reduction in the amount of torque delivered to the drive wheels. The Powertrain Control Module (PCM) reduces delivered torque by retarding the ignition timing and commanding the electronic throttle actuator.
If desired, the traction control system may be disabled by the vehicle operator. In order to disable the system, press the traction assist switch with the engine running. The traction control remains disabled until the ignition is cycled or until the traction assist switch is pressed again.
The automatic engagement feature may be programmed so that the traction control system activates or does not activate automatically at the start of each ignition cycle. In order to change the status of the automatic engagement feature, perform the following procedure:
Important: Failure to follow the correct procedure may cause DTC C0283 to set in EBCM memory.
The BRAKE indicator is located in the Instrument Panel Cluster and illuminates within the following conditions:
The ABS indicator is located in the Instrument Panel Cluster and illuminates within the following conditions:
When the ABS indicator is commanded on, loss of ABS function is indicated. The base brake system may function normally.
The traction control system uses two indicators in order to keep the vehicle operator informed of the traction control system status. The EBCM performs a two second bulb check on both indicators at power-up.
The TRACTION OFF indicator is used to show the operational status of the traction control system. If the traction control system is disabled by the vehicle operator or by the EBCM, the TRACTION OFF indicator illuminates.
The LOW TRACTION indicator is used to alert the operator when the vehicle is experiencing a traction control event. The indicator illuminates when the vehicle experiences a traction control event for 500 milliseconds. The LOW TRACTION indicator remains on for 2 seconds or until the traction control event is complete.
