Malfunction Indicator Lamp: Testing and Inspection

Chart A-1:

Chart A-1 Wiring Diagram:

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 control the light and turn it "ON" by providing a ground path through CKT 419.



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

1. "SERVICE ENGINE SOON" light should be "ON."

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.


DIAGNOSTIC AIDS:

If the engine runs OK, check:

^ Faulty light bulb.
^ CKT 419 open.
^ Gage fuse #16



If the engine cranks but will not run, check:

^ Continuous battery-fusible link open.
^ Ignition CKT 439 to ECM open.
^ ECM fuse #17.
^ Poor connection to ECM.