Key-On System Initialization

At key-on, the BCM performs a check to see if the Electronic Brake Control Module (EBCM) is responding the BCM inputs. After the ignition is moved to the RUN position, the BCM grounds the diagnostic enable line (circuit 856). See Figure . When the diagnostic enable line is grounded, the EBCM should respond by grounding the ABS Fault line (circuit 825) until the diagnostic enable line is allowed to return to 12 volts. If the initialization test fails, the following BCM codes may set.

The BCM monitors the status of the diagnostic enable line at all times. If the voltage state on this circuit does not match the commanded state, Code B421 will set. For more information, seeDTC B421: BCM OUTPUT DRIVER NO. 2 FAILURE  under DIAGNOSTIC TESTS.

If the EBCM does not respond properly to the key-on initialization test (by grounding the ABS Fault line), Code B480 will set. For more information, see DTC B480: LOSS OF ANTI-LOCK DATA  under DIAGNOSTIC TESTS.

BCM Code B481 will set if the ABS fault line remains grounded for approximately 2-1/2 minutes. For more information, see DTC B481: ANTI-LOCK FAULT  under DIAGNOSTIC TESTS.