ECM Check, Service Engine Soon Light On At All Times Or Won't Flash Code 12
The ECM check determines why SERVICE ENGINE SOON light remains on, or does not flash Code 12. Normally, ECM will not recognize a fault for at least 10 seconds after engine start-up. If SERVICE ENGINE SOON light remains on, ECM has lost battery power, ground, or the signal that turns SERVICE ENGINE SOON light off. When engine is started, ECM grounds terminal A10 to turn off SERVICE ENGINE SOON light. ECM alternately grounds and opens terminal A10 to flash trouble code.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- This tests for a short to battery voltage in wire to remote lamp driver terminal "C", or a faulty remote lamp driver. Normal reading is 9-11 volts.
- This tests if problem is related to ECM, or remote lamp driver. Normally, grounding remote lamp driver terminal "C" should turn light off. If light goes out when terminal "C" is grounded, problem is related to ECM and its wiring. If light does not go out, problem is related to remote lamp driver and its wiring.
- Normally, grounding ECM terminal A10 should turn light off. If light stays on, there is an open in circuit between ECM harness terminal A10 and remote lamp driver terminal "C".
- This tests for open ECM circuit No. 451 to diagnostic terminal "B" in ALDL connector. The light should flash Code 12 when ECM terminal A6 is grounded.
- This tests for proper voltage supply to ECM. Both readings should be more than 9 volts. Voltage to ECM terminal C14 comes from ignition switch. Terminal C16 has constant battery voltage for long term memory.
- This tests 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 PROM is not installed in the ECM. If Code 51 is not flashed, ECM is faulty.