Entering Diagnostic Display Mode
Ground pin "H" to pin "A" of ALDL connector. Connector is located behind left side of instrument panel, to the right of parking brake. See Fig 1 . Turn ignition switch to RUN position (engine off). Diagnostic display mode will remain enabled as long as pin "H" is grounded, serial data link communications has not been initiated, and vehicle speed is less than 5 MPH.
About 4 seconds after ALDL pin "H" is grounded, EBCM will begin flashing code sequence. Sequence will begin with Code 12, signaling beginning of fault code display. Each stored code will be displayed 3 times. After all codes have been displayed, sequence will repeat starting with Code 12.
Some codes can only be read through the ALDL connector using the Tech 1 Diagnostic Computer.