Chart A-1, Won't Flash Code 12 No Check Engine Light: Notes

There should always be a steady CHECK ENGINE light when the ignition is on and engine off. Battery voltage is supplied directly to the light bulb. The Electronic Control Module (ECM) controls the light and turns it on by providing a ground path through the Red wire from the ECM to the bulb.

1. Battery feed terminals C16 and B1 are protected by a fusible link in fuse/relay block, located near the battery.
2. If terminals C16 and B1 have voltage, the ECM grounds or the ECM are faulty.
3. Using a test light connected to 12 volts, probe each of the system ground circuits to ensure good ground is present.