Malfunction Indicator Lamp: Testing and Inspection

No "Service Engine Soon" Light:

"Service Engine Soon" Light Wiring Diagram:

CIRCUIT DESCRIPTION:

There should always be a steady "SERVICE ENGINE SOON" (SES) light when the ignition is "ON" and engine stopped. The engine control module (ECM) will turn the light "ON" by grounding CKT 419 at the ECM.


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

1. Probing CKT 419 to ground creates an alternate ground. If the "SERVICE ENGINE SOON" (SES) light comes "ON," this verifies that the trouble is not in the lamp portion of the circuit.


DIAGNOSTIC AIDS:

^ Engine runs OK, check:
^ Faulty light bulb.
^ CKT 419 open,
^ Gage fuse blown. This will result in no stop lights, oil or generator lights, seat belt reminder, etc.

If engine cranks but won't run, use Chart A-3.