Chart A-2, Won't Flash Code 12 Check Engine Light On Steady

The CHECK ENGINE light should remain on when ignition switch is in ON position and engine is not running. When diagnostic terminal is grounded, ECM will flash a Code 12, followed by any additional fault codes. A steady CHECK ENGINE light might be caused by a short to ground or an open diagnostic terminal.

1. Checks for a grounded light circuit.
2. Checks if problem is an open circuit in the diagnostic terminal or a faulty ECM.

Fig 1: Chart A-2, Flow Chart, Won't Flash Code 12, Check Engine Light On Steady

Courtesy of GENERAL MOTORS CORP.

Fig 2: Chart A-2, Schematic, Won't Flash Code 12, Check Engine Light On Steady

Courtesy of GENERAL MOTORS CORP.