Chart A-2, Won't Flash Code 12, (Service Engine Soon Light On Steady)
The SERVICE ENGINE SOON (SES) light should illuminate with ignition on and engine off. The ECM controls the SES light and turns it on by providing a ground path through circuit No. 419. With the diagnostic terminal grounded, the SES light should flash a Code 12, followed by any trouble codes stored in memory.
A steady light suggests a short to ground in the SES light control circuit No. 419, or an open in diagnostic circuit No. 451. A steady but dim SES light indicates failure of Quad-Driver.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- If there is a problem with ECM, causing Scan tester to not read serial data, the ECM should not flash Code 12. If Code 12 is flashing, check circuit No. 451 for short to ground. If Code 12 does flash, ensure Scan tester is working properly by testing it on a known good vehicle. If Scan tester is working properly and circuit No. 461 is okay, the MEM-CAL or ECM may be the cause of NO ALDL fault.
- If SES light goes off when ECM connector is disconnected, circuit No. 419 is not shorted to ground.
- This step checks for an open diagnostic circuit No. 451.
- At this point, the SES light wiring is okay. The problem is a faulty MEM-CAL or ECM. If Code 12 does not flash, the ECM should be replaced using the original MEM-CAL. Replace the MEM-CAL only after trying another ECM, as faulty MEM-CAL is usually not the cause of this fault.