#2 - Check Engine Light ON and Won't Flash Code 12

Check Engine Light (MIL) Circuit:

Chart 2 Won't Flash DTC 12 / MIL ON Steady:

There should always be a steady "CHECK ENGINE" Light when the ignition is "on" and engine stopped. Battery ignition voltage is supplied to the light bulb. The Electronic Control Module (ECM) will turn the light on by grounding circuit "64" or "10" at the ECM.

With the diagnostic terminal grounded, the light should flash a Code 1 2, followed by any trouble code(s) stored in memory.

A steady light suggests a short to ground in the light control circuit "64" or "10" or an open in diagnostic circuit "8" or "69".

1. If the light goes off when the ECM connector is disconnected, then circuit "64" or "10" is not shorted to ground. Also, check the connector terminals physically for proper contact at this time.
2. This step will check for an open diagnostic circuit "8" or "69".
3. At this point the "CHECK ENGINE" light wiring is okay. The problem is a faulty ECM connector or ECM.