The Electronic Brake (and Traction) Control Module (EBCM/EBTCM) performs a series of self tests. These tests inspect all of the systems (electronic and hydraulic) for any problems.

This test takes place under the following conditions:

When a problem exists, the EBCM/EBTCM sets a Diagnostic Trouble Code (DTC) and/or illuminates an indicator lamp.

The brake system uses a conventional diagonally split brake system and an add-on type ABS type unit. The brake system operates normally while the antilock brake system monitors wheel speeds and brake pedal position.

The conventional system continues to operate normally until the EBCM/EBTCM detects a wheel beginning to slip. At this point, the brake system transfers from normal braking to the antilock braking mode. The antilock brake system remains in control until one of the following conditions occurs:

The purpose of the Antilock Brake System (ABS) is in order to maintain vehicle maneuverability under severe braking conditions on most road surfaces.

The ABS/TCS system monitors the speed of each wheel during a braking maneuver.

The Electronic Brake (and Traction) Control Module (EBCM/EBTCM) processes these values in order to produce command controls. These command controls prevent the braked wheels from slipping.

The BPMV regulates brake fluid pressure based on road conditions as interpreted by the EBCM/EBTCM, regardless of the master cylinder output pressure.

The BPMV can maintain or adjust the brake fluid pressure to the brake calipers under ABS conditions. The BPMV may not increase the pressure above the level of pressure applied from the master cylinder.

However, during TCS operations, the modulator may apply pressure to the front brake calipers if the EBCM/EBTCM requires that a wheel be slowed or regulated.

The EBCM/EBTCM performs an automatic test when the ignition is turned to RUN. This test occurs one time for each ignition cycle.

The self test cycles the following components in order to inspect the component operation:

If any malfunction is detected, the EBCM/EBTCM will set a Diagnostic Trouble Code (DTC).

The self test may be heard and felt while taking place. The self test is a normal mode of operation.

The traction control system is designed in order to maintain traction and reduce wheel slip at the front drive wheels on slippery surfaces during acceleration. The system is designed in order to operate at all vehicle temperatures. The traction control system reduces wheel slip by the use of engine torque management and brake intervention.

The Electronic Brake (and Traction) Control Module (EBCM/EBTCM) monitors the front and the rear wheel speeds through the wheel speed sensors.

If the EBCM/EBTCM detects front wheel slip at any time during acceleration, the EBCM/EBTCM requests that the PCM to bring excess engine torque into a specific range. This is accomplished via 2 high speed Pulse Width Modulated (PWM) circuits between the EBCM/EBTCM and the PCM .

The PCM adjusts the spark firing angle and the engine fueling. The PCM reports the modified torque value back to the EBCM/EBTCM.

At the same time, the EBCM/EBTCM may complete the following actions:

The isolation valves isolate the front brake hydraulic circuits from the master cylinder and the rear brake hydraulic circuits. Once the front brake hydraulic circuits are isolated, pressure may be applied to the front wheels without affecting any other brake hydraulic circuit. The EBCM/EBTCM turns ON the BPMV pump motor in order to apply pressure. The EBCM/EBTCM begins cycling the BPMV's inlet and outlet valves.

The inlet and the outlet valve cyclings aid in obtaining the maximum road surface traction in the same manner as the antilock braking mode. The difference between traction control mode and antilock braking is indicated in the following list:

There are two pressure relief valves in the BPMV. This is because the BPMV pump motor supplies more brake fluid volume than required during traction control modes. The pressure relief valves allow excess brake fluid volume to be returned to the master cylinder reservoir.

If the brakes are manually applied at any time during the traction control mode, the BPMV pressure switch and the brake switch signal the EBTCM. The EBTCM disables traction control and allows manual braking.

Manual braking also overrides the traction control system through the use of the isolation valves. The isolation valves act as one way check valves. This allow manual brake fluid pressure to be applied to the brake hydraulic system.

Spare Tire

Using the compact spare supplied with the vehicle will not affect the performance of the ABS/TCS system.

Replacement Tires

The tire size is important for the proper performance of the ABS/TCS system. Replacement tires should be at the same size load range and construction as the original tires. Replace the tires in axle sets. Ensure that you replace the tires using tires of the same TPC (Tire Performance Criteria) specification number. Use of any other tire size or type may seriously affect the ABS/TCS operation. For more information on original equipment and replacement tires, refer to Tire Description Tires and Wheels.

Important: Red BRAKE warning lamp illumination may indicate reduced braking ability. Refer to Brake Warning System Circuit Description in Hydraulic Brakes for diagnosing BRAKE warning lamp operation.

BRAKE Warning Lamp

The red BRAKE warning lamp in the instrument cluster illuminates in order to alert the driver to one of the following conditions:

The following conditions cause illumination of the BRAKE warning lamp:

ANTILOCK Indicator

The EBCM/EBTCM lights the amber ANTILOCK indicator (located in the instrument panel cluster) when an ABS malfunction is detected. The ANTILOCK indicator informs the driver that a condition exists which partially or totally inhibits ABS functions.

Important: Illumination of the amber ANTILOCK indicator without illumination of the brake warning lamp indicates that the antilock braking is no longer available. Power assisted braking without antilock braking is still available. Use procedures in this section for diagnosing ANTILOCK indicator conditions.

When the ANTILOCK indicator is illuminated, but the BRAKE warning lamp is not illuminated, the normal power assisted braking is still available.

When both the BRAKE and the ANTILOCK indicators are illuminated, something is causing a low fluid condition in the brake hydraulic system.

Important: When the vehicle is equipped with traction control, any symptom which lights the ANTILOCK indicator also lights the TRACTION OFF indicator. When both indicators are on, follow the ANTILOCK indicator diagnosis.

TRACTION OFF Indicator

When the ignition switch is first turned to RUN, the TRACTION OFF indicator lights for approximately 2-4 seconds. When only the TRACTION OFF indicator remains ON beyond 4 seconds, the cause may be one of the following conditions:

TRACTION ACTIVE Indicator (Oldsmobile)

The EBTCM always alerts the driver when the traction control system (TCS) is activated. This is done by illuminating a TRACTION ACTIVE indicator.