When wheel slip is noted during a brake application, the ABS will enter Antilock mode. During Antilock braking, hydraulic pressure in the individual wheel circuits is controlled 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 hydraulic pressure to each wheel brake. However, it cannot increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.

During Antilock braking, a series of rapid pulsation's will be felt in the brake pedal. These pulsation's are caused by the rapid changes in position of the individual solenoid valves as they respond to their desired wheel speed. 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 pulsation's should be considered normal during Antilock operation.

Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking should be no different than previous systems. Maintaining a constant force on the pedal will provide the shortest stopping distance while maintaining vehicle stability.

When the EBTCM senses a wheel slip the EBTCM isolates the system by closing the Inlet valve and keeps the Outlet valve closed in the Brake Pressure Modulator Valve (BPMV). This holds the pressure steady on the brake so hydraulic pressure does not increase or decrease.

If during the pressure hold mode the EBTCM still senses wheel speed slip it will decrease pressure to the brake. It does this by leaving the Inlet valve closed and opening the Outlet valve in the BPMV. The excess fluid is stored in the accumulator until it can be returned to the reservoir by the return pump.

If during the pressure hold or decrease mode the EBTCM senses that the wheel speed is too fast it will increase pressure to the brake. It does this by opening the Inlet valve and closing the Outlet valve in the BPMV. The increased pressure comes from the master cylinder and is related to the pressure applied to the brake pedal.

Traction control will not have any effect on the operation of the vehicle until the control module detects one or both of the front wheels rotating faster than the rear wheels. At this time the Electronic Brake and Traction Control Module (EBTCM) will request the Powertrain Control Module (PCM) to reduce the amount of torque applied to the drive wheels. The PCM does this by retarding timing and selectively turning off fuel injectors. The EBTCM will apply the rear brakes, thus reducing torque to the rear wheels. Once the rear wheels begin to rotate at the same speed as the front wheels, the system will return full control to the driver. During Traction Control mode, if the brake is applied to only one rear wheel, most of the torque from the engine will be directed to the other rear wheel which will improve the traction of the vehicle.

The braking is accomplished by closing the TCS Master Cylinder Isolating Valve, this isolates the master cylinder from the rest of the system. The TCS Prime valve opens to allow the pump to get brake fluid to build pressure for braking. The drive wheel circuit solenoids are energized as needed to allow for pressure hold, pressure increase, or pressure decrease.

The TCS may be deactivated by the driver if desired. In order to deactivate the TCS with the engine running, depress the Traction/Suspension Control switch. The system will remain deactivated until the ignition switch is cycled, or the switch is pressed again.

The Speed Dependent Steering System (Magna Steer®), incorporates its controller into the EBTCM.

Magna Steer® DTC C1241 will not cause any indicators to turn on.

Refer to DTC C1241 Magnasteer Malfunction in Variable Effort Steering for DTC C1241 diagnostics.

The tire size is important for the performance of the ABS/TCS. The replacement tires should be the same size load range and construction as the original tires. Replace the tires in axle sets and only with tires of the same tire performance criteria specification number. Use of any other tire size or type may seriously affect ABS/TCS operation. For information on replacement tires for this vehicle, Refer to Replacement Tires in Tires and Wheels.

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. The BRAKE warning lamp will stay illuminated until the condition has been repaired. Refer to Brake Warning System Description in Hydraulic Brakes.

The Antilock Indicator (ABS) is located in the instrument cluster and will illuminate if a malfunction in the ABS is detected by the Electronic Brake and Traction Control Module (EBTCM). The Antilock Indicator informs the driver that a condition exists which results in turning off the Antilock brake and traction control function. If only the Antilock Indicator is on, normal braking with full power assist is available. If the BRAKE and Antilock Indicators are on, a problem may exist in the hydraulic brake system. Refer to Brake System Testing in Hydraulic Brakes. Conditions for the Antilock Indicator to turn on are as follows:

1. ABS malfunction detected. As previously described, the Antilock Indicator turns on when a problem has been found in the ABS. The Antilock Indicator indicates that the ABS and TCS have been disabled.
2. Instrument Panel Cluster bulb check. When the ignition is turned to on, the Antilock Indicator will turn on for approximately three seconds and then turn off.

•	Illumination of the BRAKE warning Indicator may indicate reduced braking ability.

•	Illumination of the Antilock 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.

•	Refer to Brake System Testing in Hydraulic Brakes for diagnosis of any condition which causes the BRAKE warning Indicator to illuminate.

Several messages related to the ABS/TCS may be displayed on the Driver Information Center (DIC), they are:

1. ABS ACTIVE: This message is displayed when ABS is active.
2. SERVICE ABS: This message is displayed when an ABS fault exists.
3. SERVICE TRACTION SYS: This message is displayed when an ABS fault exists.
4. SERVICE TRACTION SYSTEM: This message is displayed when a TCS fault exists.
5. TRACTION SYS ACTIVE: This message is displayed when TCS is active.
6. TRACTION OFF: This message is displayed when TCS is turned off.
7. TRACTION ON: This message is displayed for 3.5 seconds when TCS is turned on.