Chart A-2 Won't Flash DTC 12 No Serial Data MIL On Steady

Chart A-2:

"Service Engine Soon" Light Wiring Diagram:

***UPDATED BY TSB # 92-6E-26 DATED NOVEMBER 1992




CIRCUIT DESCRIPTION:

There should always be a steady "SERVICE ENGINE SOON" light when the ignition is "ON" and engine stopped. Ignition voltage is supplied to the light bulb. The ECM will turn the light on by grounding CKT 419.

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's 450 or 451.


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.


1. Checks circuit 419 to ground

2. This step will check for an open diagnostic CKT 451.

3. 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.