Malfunction Indicator Lamp: Testing and Inspection

Chart A-1:

Wiring Diagram For Service Engine Soon Light:

CIRCUIT DESCRIPTION:

There should always be a steady "SERVICE ENGINE SOON" (SES) light when the ignition is "ON" and engine stopped. Battery is supplied directly to the light bulb. The Electronic Control Module (ECM) will control the light and turn it "ON" by providing a ground path through CKT 419 to the ECM.


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

1. Use J 35616 or equivalent tool kit to probe ECM harness terminals, so that you don't damage them.

2. Using a test light connected to 12 volts probe each of the system ground circuits to be sure a good ground is present. See ECM CONNECTOR IDENTIFICATION in ELECTRICAL AND ELECTRONIC DIAGRAMS for ECM pin locations of ground circuits.

3. If the fusible link is blow, refer to wiring diagram for complete circuit.

4. Make sure to check all 239 circuits if the ECM fuse is blown. Refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for ECM wiring information. The SIR system Diagnostic Energy Reserve Module (DERM) must be connected to the instrument panel harness or switched ignition voltage will not be supplied to the ECM and this will not allow the engine to start. Refer to SUPPLEMENTAL INFLATABLE RESTRAINT (SIR) DIAGNOSIS under /PASSIVE RESTRAINT/BODY ELECTRICAL SAFETY AND ENTERTAINMENT.

Check all 703 circuits if the AIR BAG fuse is blown. See ECM WIRING DIAGRAMS for information.

DIAGNOSTIC AIDS:

Engine runs OK, check:

^ Faulty light bulb
^ CKT 419 open

Engine cranks but will not run:

^ Continuous battery - fusible link open
^ ECM fuse open
^ Battery CKT 480A and 480B to the ECM open
^ Ignition CKT 239 to the ECM open
^ Poor connection to ECM
^ Faulty ECM ground circuit(s)
^ VATS power supply