Chart A-2 No Code 12 Light ON Steady

Fig. 019 - Wiring Diagram for Chart A-2 Code 12 Will Not Flash. VIN W:

CHART A-2

NO ALDL DATA OR WON'T FLASH CODE 12

"SERVICE ENGINE SOON" LIGHT ON STEADY"

2.8L "A & J" SERIES (PORT)

Circuit Description:
There should always be a steady "Service Engine Soon" light, when the ignition is "ON" an engine stopped. Battery ignition voltage is supplied to the light bulb. The Electronic Control Module (ECM) will turn the light "ON" by grounding CKT 419 at the ECM.
With the diagnostic terminal grounded, the light should flash a Code 12, followed by any trouble code(s) stored in memory.
A steady light suggests a short to ground in the light control CKT 419, or an open in diagnostic CKT 451.

Fig. 018 - Chart A-2 - Code 12 Will Not Flash:

Test Description:
Step numbers refer to step numbers on diagnostic chart.
1. If Code 12 is flashing check for CKT 451 short to ground.
2. If the light goes "OFF" when the ECM connector is disconnected, CKT 419 is not shorted to ground.
3. This step will check for an open diagnostic CKT 451.
4. At this point the "Service Engine Soon" light wiring is OK. The problem is a faulty ECM or Mem-Cal. If Code 12 does not flash, the ECM should be replaced using the original Mem-Cal. Replace the Mem-Cal only after trying an ECM, as a defective Mem-Cal is an unlikely cause of the problem.