Chart A-2, Service Engine Soon Light Will Not Go Out Or Flash
SERVICE ENGINE SOON light is attached to IPC. It is powered by circuit No. 39. PCM completes ground to turn light on. Light will be on while engine is not running. With engine running, a steady light indicates a fault code is set.
With diagnostic terminal grounded, light should flash Code 12, followed by any stored trouble codes. A steady light could be caused by a short to ground in circuit No. 419.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- If light goes off when PCM connector is unplugged, PCM drive circuit is not shorted to ground.
- This step will check for an open diagnostic circuit No. 451 (terminal "B" of ALDL).
- At this point, SERVICE ENGINE SOON light wiring is okay. Problem is a faulty PCM or MEM-CAL. If Code 12 does not flash, PCM should be replaced using original MEM-CAL. Replace MEM-CAL only after trying a PCM, as a defective MEM-CAL is an unlikely cause of problem.