Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
A-2, Mil (Service Engine Soon) LT On At All Times Or Will Not Flash DTC 12 (With M/T)
The ECM check determines why MIL remains on, or does not flash DTC 12. Normally, ECM will not recognize a fault for at least 10 seconds after engine start-up. If MIL remains on, ECM has lost battery power, ground, or the signal that turns MIL off. When engine is started, ECM grounds terminal A10 to turn off MIL light. ECM alternately grounds and opens terminal A10 to flash DTC.
- This tests for a short to battery voltage in wire to MIL driver terminal "C", or a faulty MIL driver. Normal reading is 9-11 volts.
- This tests if problem is related to ECM, or MIL driver. Normally, grounding MIL 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 MIL driver and its wiring.
- Normally, grounding ECM terminal A10 turns light off. If light stays on after grounding terminal A10, there is an open in circuit No. 487 between ECM terminal A10 and MIL driver terminal "C".
- This tests for open circuit No. 451 between ECM and diagnostic terminal "B" in DLC. The light should flash DTC 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 DTC 51 to flash even though PROM is not installed in the ECM. If DTC 51 is not flashed, ECM is faulty.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.