For the proper diagnostic procedure for either the entire ABS system or a single component of the system, a scan tool (DRB or equivalent) is necessary. Because of the complexity of the ABS system and the importance of correct system functioning, it is a good idea to have a qualified automotive mechanic test the system if any problems have been detected.
The self-diagnostic ABS start up cycle begins when the ignition switch is turned to the ON position. An electrical check is completed on the ABS components, such as the wheel speed sensor continuity and other relay continuity. During this check the amber anti-lock light is turned on for approximately 1-2 seconds.
Further functional testing is accomplished once the vehicle is set in motion.
If the vehicle is not set in motion within 3 minutes from the time the ignition switch is set in the ON position, the solenoid test is bypassed, but the pump/motor is activated briefly to verify that it is operating correctly.
For the ABX-4 system, fault codes are kept in a non-volatile memory until either erased by the DRB or erased automatically after 50 ignition cycles (key ON-OFF cycles). The only fault that will not be erased after the 50 ignition cycles is the CAB fault. On the Teves Mark 20 system, DTCs are kept in the controller's memory until erased with the DRB scan tool, or they are erased automatically after 3,500 miles or 255 key cycles which ever occurs first. A CAB fault can only be erased by the DRB scan tool. More than one fault can be stored at a time. The number of key cycles since the most recent fault was stored is also displayed. Most functions of the CAB and ABS system can be accessed by the DRB scan tool for testing and diagnostic purposes.
To read the Diagnostic Trouble Codes (DTC's) perform the following:
- Inspect the ABS components and connectors for damage and/or proper connections. Keep in mind that the brake light circuit also provides an input to to the ABS system. If the brake lights do not work, they must be fixed before proceeding.
- Connect a DRB or equivalent scan tool to the Data Link Connector (located under the drivers side instrument panel). A scan tool must be used to access these codes.
- Turn the ignition to the ON position. Wtih the scan tool, select "ABS".
- Use the scan tool to select "Inputs/Outputs", and read the brake switch status. While pressing on the brake pedal, check the scan tool display. Select "Read DTC" and record any trouble codes which may appear. Sometimes, the cause of one trouble code may trigger additional codes to be set. If more than one code appear, a certain sequence of tests may be necessary. The beginning of each test will indicate if another test should be performed first.
- Once the problem is corrected, use the scan tool to erase the trouble code(s).