ABS Operation

ANTILOCK BRAKING MODE
When wheel slip is noted during a brake application, the ABS will enter the antilock mode. During antilock braking, the hydraulic pressure in the individual wheel circuits is controlled in order to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase the hydraulic pressure to each wheel brake. However, the ABS cannot increase the hydraulic pressure above the amount that the master cylinder transmits during braking. During antilock braking, a series of rapid pulsations will be felt in the brake pedal. The rapid changes in the position of the individual solenoid valves as they respond to the desired wheel speed causes the pulsations. This pedal pulsation is present during antilock braking and will stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves rapidly cycle. During antilock braking on dry pavement, the tires may make intermittent chirping noises as they approach slipping. These noises and pedal pulsations are normal during antilock operation. Brake pedal operation during normal braking should be no different than previous systems. Maintaining a constant force on the pedal provides the shortest stopping distance while maintaining vehicle stability.

PRESSURE HOLD
When the EBCM/EBTCM senses wheel slip, the EBCM/EBTCM closes the Inlet valve and keeps the Outlet valve closed in the BPMV in order to isolate the system. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.

PRESSURE DECREASE
If during the pressure hold mode the EBCM/EBTCM still senses wheel slip, the EBCM/EBTCM will decrease the pressure to the brake. The Inlet valve is left closed and the Outlet valve is opened. The excess fluid is stored in the accumulator until the return pump can return the fluid to the master cylinder.

PRESSURE INCREASE
If during the pressure hold or the pressure decrease mode the EBCM/EBTCM senses that the wheel speed returns to normal or increases, the EBCM/EBTCM will increase the pressure to the brake. The Inlet is opened and the Outlet valve is closed. The increased pressure comes from the master cylinder and is related to the pressure applied to the brake pedal.

TRACTION CONTROL
Enhanced Traction System (ETS)
The ETS is designed to limit wheel slip during acceleration when one or more of the drive wheels are accelerating too rapidly and the brake switch is off.
The EBTCM monitors wheel speed slip through the ABS wheel speed sensors then processes wheel speed sensor data and sends a desired wheel torque value to the Powertrain Control Module via a Class 2 Serial Data Line signal. The PCM then calculates and employs control of the wheel slip/wheel torque by utilizing up to three different methods as follows:
^ By retarding ignition timing.
^ By shutting off up to three injectors.
^ By up-shifting the transmission thereby reducing engine torque providing stability and traction.

If the EBTCM determines that the engine torque reduction is not sufficient to minimize wheel spin, it will repeat the above sequence.
The ETS will be enabled when the Traction Control switch is in the ON position (TRAC OFF indicator not illuminated), the catalytic converter temperature is within the normal operating range and the engine coolant temperature is within normal operating range. The ETS will be disabled under the following conditions:
^ The Traction Control switch is in the OFF position.
^ The EBTCM senses a valid brake switch input.
^ The park brake is engaged.
^ Catalytic converter temperature rises above the normal range.
^ Engine coolant temperature is outside the normal operating range.
^ The PCM sets a DTC that turns on the CHECK ENGINE indicator.
^ The EBTCM sets any DTC that effects the ETS operation.

TRACTION CONTROL SYSTEM (TCS)
Traction control will not have any effect on vehicle operation until the control module detects one or both of the front wheels rotating faster than the rear wheels. At this time, the EBTCM will request the PCM to reduce the amount of torque applied to the drive wheels. The PCM retards the timing and turns off the supercharger (if equipped) and the fuel injectors similar to the ETS system outlined above. The EBTCM applies the front brakes in order to reduce the torque to the front wheels. Once the front wheels begin to rotate at the same speed as the rear wheels, the system will return full control to the driver. During the traction control mode, if the brake is applied to only one front wheel, most of the engine torque will be directed to the other front wheel, thus improving the vehicle traction. Closing the TCS master cylinder isolating valve isolates the master cylinder from the rest of the system. The TCS prime valves open in order to allow the pump to get the brake fluid to build the pressure for braking. The drive wheel circuit solenoids are energized as needed in order to allow for pressure hold, pressure increase, or pressure decrease. The driver can deactivate the TCS, if desired. In order to deactivate the TCS with the engine running, depress the Traction Control switch. The TRAC OFF Indicator in the Driver Information Display will illuminate. The system remains deactivated until the ignition switch is cycled, or the switch is pressed again.

MAGNETIC STEERING VARIABLE STEERING (MSVA)
The Magnetic Steering Variable Steering (MSVA) system also known as (MAGNASTEER(R)) incorporates a controller into the EBCM/EBTCM. The EBCM/EBTCM receives inputs from wheel speed sensors. The EBCM/EBTCM processes this information and controls the amount of current to the MSVA actuator to vary the rate of input torque required at the steering gear. A DTC is stored in the EBCM/EBTCM only for a MSVA malfunction. A MSVA DTC C1241 will not cause the ABS or TRAC OFF indicators to go on.

TIRES WITH ABS/ETS/TCS/TIM
The compact spare tire rotates faster than the standard tires that are original equipment. The EBCM/EBTCM compensates for this faster rotation but a DTC C1245 will set and Low Tire Indicator will illuminate until the tire is repaired or replaced. Then the RESET switch (located in the fuse panel) must be pushed to reset the Tire Inflation Module (TIM) system that is part of the EBCM/EBTCM. Refer to Tire and Wheel Specifications in Wheels, Tires and Alignment for information on replacement tires.

BRAKE WARNING INDICATOR
The red BRAKE Indicator in the instrument cluster will illuminate to warn the driver of conditions in the brake system which may result in reduced braking ability. The indicator will also illuminate when the parking brake is applied or not fully released, or if the brake fluid level switch is closed (closed is when the Brake fluid is low in the master cylinder reservoir). When the Brake fluid level switch is closed (low condition) a DTC C1247 is set in the EBTCM. The BRAKE warning Indicator will stay illuminated until the condition has been repaired.

ABS INDICATOR
The ABS indicator is located in the instrument cluster and will illuminate if a malfunction in the ABS is detected by the Electronic Brake Traction Control Module (EBCM/EBTCM). The ABS indicator informs the driver that a condition exists which results in turning off the antilock brake and traction control function. If only the ABS indicator is on, normal braking with full power assist is available. If the BRAKE and ABS indicators are on, a problem may exist in the hydraulic brake system. Refer to Brake System Testing in Hydraulic Brakes. Conditions for the ABS indicator to turn on are as follows:
^ ABS malfunction detected. As previously described, the ABS indicator turns on when a problem has been found in the ABS. The ABS indicator indicates that the ABS, ETS, and TCS have been disabled.
^ Instrument panel cluster bulb check. When the ignition is turned to RUN, the ABS indicator will turn on for approximately 3 seconds and then turn off.
- Illumination of the BRAKE warning Indicator may indicate reduced braking ability.
- Illumination of the ABS indicator without the BRAKE warning Indicator on indicates only that antilock braking is no longer available.
- Power assisted braking without antilock control is still available.

TRAC OFF INDICATOR
The TRAC OFF indicator located in the Driver Information Display will illuminate to notify the driver of the following:
^ ETS/TCS operation has been inhibited by the PCM.
^ The driver has switched off ETS/TCS by pressing the Traction Control switch.
^ The EBTCM sets a DTC that effects the operation of the ETS/TCS.

As a bulb check procedure, the EBTCM will command the TRAC OFF indicator on for 3 seconds when the EBTCM receives Ignition power.

LOW TRAC INDICATOR
The LOW TRAC indicator is located in the Driver Information Display. The LOW TRAC indicator will illuminate to alert the driver of a low traction situation and to inform the driver the ETS/TCS is operating. It does not operate during ABS operation. The LOW TRAC indicator will remain on for approximately 3 to 4 seconds after the ETS/TCS event is complete.
As a bulb check procedure, the EBTCM will command the LOW TRAC indicator on for approximately 3 to 4 seconds when the EBTCM receives Ignition power.