ECM Check "Service Engine Soon" Light On At All Times Or Won't Flash Code 12
The ECM check is made to determine why the "SERVICE ENGINE SOON" light remains on or does not flash Code 12. Normally, the ECM will not recognize a fault for at least 10 seconds after start up. If the "SERVICE ENGINE SOON" light remains on, the ECM has lost battery power, ground, or the signal that turns the "SERVICE ENGINE SOON" light off. When engine is started, the ECM grounds terminal "A10" to turn off the "SERVICE ENGINE SOON" light. It alternately grounds and opens terminal ECM "A10" to flash a code.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test checks for a short to battery voltage in wire to terminal "C" of remote lamp driver or for a faulty remote lamp driver. Normal reading is 9-11 volts.
- This test checks if problem is related to the ECM or the remote lamp driver. Normally, grounding terminal "C" of remote lamp driver should turn light off. If it does, problem is related to the ECM and its wiring. If not, it is related to the remote lamp driver and its wiring.
- Grounding terminal "A10" at ECM and finding light on, indicates an open in circuit No. 487 to terminal "C" of remote lamp driver. Normally, grounding ECM terminal "A10" should turn light off.
- This test checks for open circuit No. 451 from ECM to diagnostic terminal in ALDL connector. The light should flash Code 12 when ECM terminal "A6" is grounded.
- This test checks for proper voltage supply to ECM. Both readings should be over 9 volts. Voltage to ECM terminal "C14" comes from ignition switch, and terminal "C16" has constant battery voltage for long term memory.
- This test checks for a bad ground to ECM. Terminal "C2" is connected in the ECM.
- This test 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 does not, it means that the ECM is faulty.