Chart A-6 Check Engine Light on at All Times or No Code 12

Fig. 021 - Chart A-6 Check Engine Light On At All Times or Won't Flash Code 12.:

CHART A-6, WON'T FLASH CODE 12

1. This step checks for short to battery voltage in wire to Terminal 'C' or faulty lamp driver. Normal voltage reading is 9-11 volts.
2. This step checks to see if problem is related to the ECM or the lamp driver.
Normally, grounding Terminal 'C' should turn lamp "OFF". If it does, the problem is related to the ECM and its wiring. If not, it is related to the lamp driver and its wiring.
3. Grounding Terminal 'G' at ECM and finding light "ON" indicates an open in the wire to Terminal 'C' of lamp driver.
Normally, grounding Terminal 'G' should turn lamp "OFF".
4. This step checks for open in wire from ECM to test terminal in ALCL connector. The lamp should flash Code 12 when Terminal "5" is grounded.
5. 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.
6. Checks for a bad ground to ECM - Terminals 'A' and 'U' are connected together in the ECM.
7. 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 it doesn't, it means that the ECM is faulty.