The air antilock braking system is electronically monitored and controlled by the Bendix EC-30 electronic brake control module (EBCM).

Other system components are listed as follows.

The electronic brake control module (EBCM ) performs a brake pressure modulator valve (BPMV) modulator test each time the ignition is turned ON. Each modulator is tested in sequence electrically by energizing the hold solenoid 2 times and the exhaust solenoid once. When the brake is applied and the system is pressurized, an audible exhaust of air pressure can be heard from each of the modulators in sequence. Modulators test in the flowing order:

The sequence is performed 2 times for a total of 8 modulator tests. If modulators test out of sequence, check air lines and wiring for the correct routing to the ABS brake modulators.

The electronic brake control module (EBCM) performs an initialization test during each ignition cycle. The initialization of the EBCM occurs when the following conditions are met.

The EBCM verifies correct operation of the ABS components during initialization and sets diagnostic faults in accordance with any malfunction that is detected.

The electronic brake control module (EBCM) displays diagnostic fault messages by illuminating LEDs on the side of the EBCM. The EBCM cannot, however, display more than one diagnostic fault at a time. A displayed fault must be corrected and the system must be reset before any other fault message can be displayed. Most failures illuminate 3 LEDs. The component affected by the failure is indicated by illuminating 3 of the following red LEDs: left or right (LFT or RGT), front or rear (FRT or RER), and sensor or modulator (SEN or MOD). A fault affecting the air traction control (TC) modulator valve illuminates the traction and modulator (TRC, MOD) LEDs.

The green VLT LED is normally ON steady when the ignition is ON. A fault in the supply voltage or ground circuits to the EBCM may cause the green VLT LED to flash or turn OFF.

The red ECU LED may illuminate if there is a fault in the supply voltage or ground circuits to the EBCM or if the EBCM detects an internal malfunction.

Occasionally, an LED may fail to operate. This may make diagnosis more difficult but does not indicate that the EBCM is non-functional or needs to be replaced. Observing the LEDs at the start of each ignition cycle in order to identify an inoperative LED will aid in proper system diagnosis. This is described further in the Configuration Display section below. The EBCM may need to be replaced if more than one LED is inoperative.

The electronic brake control module (EBCM) can be observed for the proper configuration after the Electronic Brake Control Module Configuration is performed. The EBCM displays the EBCM configuration at the start of each ignition cycle. When the ignition is turned to ON, all of the LEDs illuminate momentarily and then turn OFF. Any LEDs that do not illuminate are inoperative and should be noted at this time. The EBCM then momentarily illuminates the FRT, RER, and SEN LEDs. TRC, MOD also illuminates if the vehicle is configured for traction control. This indicates the EBCM is properly configured to the vehicle. The diagnostic display then returns to normal operational status.

An amber ABS indicator located in the instrument panel cluster (IPC) is used to alert the vehicle operator of a malfunction within the ABS. The electronic brake control module (EBCM) will perform a bulb check during each ignition cycle prior to initialization. The EBCM sends a message to the serial data gateway (SDG). The SDG then sends a class 2 message to the IPC in order to command the indicator ON or OFF.

When wheel slip is noted during a brake application, the ABS enters antilock mode. During antilock braking, if the vehicle is equipped with an automatic transmission, the electronic brake control module (EBCM) sends a message to the transmission controller in order to disable torque converter lock up. If the vehicle is equipped with an exhaust brake, the EBCM also disables the exhaust brake by activating the exhaust brake disable relay. Air pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. Specific solenoid valves are provided for each wheel. The ABS can exhaust, hold, or increase air pressure to each wheel brake. However, it cannot increase pressure above the amount which is delivered from the application valve.

During an ABS event, noise may be heard as the solenoid valves rapidly cycle and air pressure is exhausted to the atmosphere. During antilock braking on dry pavement, the tires may make intermittent chirping noises as they approach slipping. These sounds are to 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 is no different than previous non-ABS systems. Maintaining constant pressure on the brake pedal provides the shortest stopping distance while maintaining vehicle stability.

The electronic brake control module (EBCM) closes the hold valve and keeps the normally closed exhaust valve closed in the air pressure modulator that regulates pressure to the slipping wheel. This is done in order to isolate the brake circuit of the slipping wheel so that the pressure in the brake circuit does not increase or decrease.

If a pressure hold does not correct the wheel slip condition, a pressure decrease occurs. The electronic brake control module (EBCM) decreases the pressure in the brake circuit of the slipping wheel by keeping the hold valve closed and opening the exhaust valve. The excess air pressure is exhausted to the atmosphere.

After the wheel slip is corrected, a pressure increase occurs. The electronic brake control module (EBCM) increases the pressure to wheel in order to reduce the speed of the wheel. The hold valve is opened and the exhaust valve is closed. The increased pressure is delivered from the application valve.

Traction control (TC) improves vehicle stability and traction during vehicle acceleration. The electronic brake control module (EBCM) compares drive wheel speeds of both wheels on the same axle to determine a loss of traction. The TC function uses the same wheel speed information and sensors that are utilized with ABS. When uneven drive wheel speeds are detected, the EBCM activates the air TC modulator valve to apply air pressure to the drive axle brake pressure modulator valve (BPMV) modulators. The EBCM than can apply brake to the slipping wheel in order to transfer torque to the gripping wheel.

Traction control (TC) can be disabled or enabled by using the TC enable/disable switch. TC can only be disabled after the ignition is turned ON. Once the ignition is cycled, the TC will default to an active status. When TC is manually disabled, TC cannot be re-enabled manually until the vehicle has a completely stopped.

The traction control low traction/off indicators are located in the traction switch. The indicators are used to alert the vehicle operator of the status of the ATC system. The traction control (TC) low traction lamp illuminates during a TC event. If there is a fault present with the TC system or if the TC has been disabled manually, the OFF indicator illuminates.

The EC-30 electronic brake control module (EBCM) does not control the trailer ABS. Trailers equipped with ABS use a separate ABS system that is independent from the vehicle ABS system. The trailer ABS indicator is located in the driver information center (DIC) and is used to alert the vehicle operator of a malfunction within the trailer ABS. The trailer EBCM sends a power line carrier (PLC) frequency across the battery positive voltage circuit to the vehicle EBCM. The vehicle EBCM turns ON the ABS indicator by supplying ground to the trailer ABS indicator control circuit. The trailer EBCM sends the PLC signal for the ABS indicator bulb check and if a malfunction is present with the trailer ABS. The trailer ABS indicator can not bulb check unless a trailer with ABS is installed to the vehicle.