The Air Antilock Braking System is electronically monitored and controlled by the Bendix EC-17 Electronic Brake Control Module (EBCM).

Other system components are listed as follows.

The 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(s) that is detected.

The 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).

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 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. 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 is used to alert the vehicle operator of a malfunction within the ABS. The EBCM will perform a bulb check during each ignition cycle prior to initialization. The EBCM must apply ground to the control circuit of the ABS lamp relay coil in order to turn OFF the ABS indicator.

When wheel slip is noted during a brake application, the ABS will enter antilock mode. During antilock braking, 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 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 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 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.