Chart A-1 No Service Engine Soon Light

Chart A-1:

Wiring Diagram For Service Engine Soon Light:

CIRCUIT DESCRIPTION:

There should always be a steady "SERVICE ENGINE SOON" light when the ignition is "ON" and engine stopped. Battery ignition voltage is supplied to the light bulb. The ECM will control the light and turn it "ON" by providing a ground path through circuit 419 to the ECM.


DIAGNOSTIC AIDS:

If the engine runs OK, check:
^ Faulty light bulb.
^ Circuit 419 open.
^ Gauge fuse blown. This will result in no oil, generator, or seat belt reminder lights.

If the engine cranks but will not run, check:
^ Continuous battery-fuse or fusible link open.
^ ECM ignition fuse open.
^ Battery circuit 240 to ECM open.
^ Ignition circuit 439 to ECM open.
^ Poor connection to ECM.