Accessing and Reading Diagnostic Trouble Codes
Fig. 5 ABS Flash Code Sequence:
ABS SELF DIAGNOSTICS (Trouble Codes)
The Electronic Brake Control Module (EBCM) contains the ABS self diagnostics. It is equipped with a self diagnostic capability that can detect and isolate ABS failures. When a failure is detected the EBCM sets a trouble code that represents that failure.
There are thirteen trouble codes that may be set by the EBCM. All of the codes except Code 72 will cause the EBCM to disable the ABS (allowing power assisted braking only) and the "Antilock" indicator to be turned "ON. Refer to "ABS Trouble Code and Symptom Table" in this section for a complete list of ABS trouble codes.
The EBCM performs an automatic (Auto) test once during each ignition cycle when the vehicle reaches approximately 4 mph. The Auto test cycles each solenoid valve and the pump motor to check component operation. If any error is detected during this test the EBCM will set a trouble code. This test may be heard and felt while it is taking place and should be considered a normal mode of operation.
The EBCM can display the trouble codes only when the "Diagnostic Service Mode" has been entered. Entering the diagnostic service mode is accomplished by either using the Tech 1 diagnostic computer, (refer to Tech 1 diagnostics in this section) or by grounding terminal "H" of the ALDL connector and using "Flash Code" diagnostics as described under "Flash Code Diagnostics."
The use of the Tech 1 diagnostic computer is recommended for diagnosing the Antilock Brake System.
FLASH CODE DIAGNOSTICS
"Flash Code" diagnostics can only be used to identify codes in EBCM history. "Flash Code" diagnostic mode cannot be initiated if the "Antilock" indicator is "ON" steady (not flashing).
To enable "Flash Code" diagnostics, ground terminal "H" of the ALDL connector, then turn the ignition "ON." "Flash Code" diagnostics will remain enabled as long as terminal "H" is grounded, serial data line communication has not been initiated, and vehicle speed is less than approximately 4 miles per hour.
About 3 seconds after ALDL terminal "H" is grounded, the EBCM will begin flashing the "Antilock" indicator, if current codes excluding 41, 45, 55, 61 and 63 are set. Current Codes 41, 45, 55, 61 and 63 can only be read through the ALDL connector using the Tech 1. The EBCM will not allow "Flash Code" diagnostics if any of these codes are set as current. If these codes are present as history codes only, they can be read through "Flash Code" diagnostics.
The flash sequence will begin with Code 12 to signal the beginning of the trouble code display. Code 12 flashes three times. Each stored code will then be displayed three times. After all codes have been displayed, the sequence will repeat, starting with Code 12.