Chart A-6, Won't Flash Code 12
- This step checks for short to battery voltage in wire to terminal "C" or faulty lamp driver. Normal reading is 9 to 11 volts.
- This step checks to see if problem is related to the ECM or lamp driver. Grounding terminal "C" should turn lamp "OFF".
- Grounding terminal "G" at ECM and finding light "ON" indicates an open in the wire to terminal "C" of lamp driver. Grounding terminal "G" should turn lamp "OFF".
- This step checks for open in wire from ECM to test terminal in ALDL connector. The lamp should flash Code 12 when terminal "5" is grounded.
- This checks for proper voltage supply to ECM, both should read over 9 volts. terminal "C" is ignition and terminal "R" is constant battery for long term memory.
- This test checks for bad ground in ECM. Terms. "A" and "U" are connected together in the ECM.
- This step distinguishes between a faulty ECM and PROM. Normal response is for Code 51 to flash even though the PROM is not installed in the ECM. If no Code 51, ECM is faulty.