ECM Check, Service Engine Soon Light On At All Times Or Won't Flash Code 12
The ECM check determines 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.
Test Number 1) 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.
Test Number 2) This tests if problem is related to the ECM or the remote lamp driver. Normally, grounding remote lamp driver terminal "C" should turn light off. If it does, problem is related to the ECM and its wiring. If not, problem is related to the remote lamp driver and its wiring.
Test Number 3) Grounding terminal A10 at ECM and finding light on, indicates an open in circuit No. 487 to remote lamp driver terminal "C". Normally, grounding ECM terminal A10 should turn light off.
Test Number 4) This tests for open ECM circuit No. 451 to diagnostic terminal in ALDL connector. The light should flash Code 12 when ECM terminal A6 is grounded.
Test Number 5) 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.
Test Number 6) This tests for a bad ground to ECM. Terminal C2 is connected in the ECM.
Test Number 7) 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.