Accessing and Reading Diagnostic Trouble Codes

Diagnostic Display Mode
To enable the diagnostic display mode, ground pin H of the ALDL connector, then turn the ignition On. The diagnostic display mode will remain enabled as long as pin H is grounded, serial data link communication has not been initiated and vehicle speed is less than 5 mph.
Approximately three seconds after ALDL pin H is grounded, the EBCM will begin the flash code sequence. The flash sequence will begin with Code 12 to signal the beginning of the fault code display. Each stored code will then be displayed three times. After all codes have been displayed, the sequence will repeat, starting with Code 12.
Some fault codes involving the solenoid valves and pump motor prevent the SERVICE ABS lamp from flashing. If one of these codes is present, the SERVICE ABS lamp will remain On and the system will be unable to enter the diagnostic display (flash codes) mode. In this case, the Tech 1 Diagnostic Computer must be used. Refer to procedure outlined under TECH 1 DIAGNOSTICS.