Chart A4-1 No Service Engine Soon Light

Chart A-1 - "Service Engine Soon" Light:

Chart A4-1:

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 circuit 419 to the ECM.

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

1. If the fuse in holder is blown refer to wiring diagram of Code 54 for complete circuit.
2. Using a test light connected to 12 volts probe each of the system ground circuits to be sure a good ground is present. For ECM pin locations of ground circuits, refer to Computers and Controls / Engine Control Module / Diagrams / ECM Terminal I.D. Diagrams

DIAGNOSTIC AIDS
Engine Runs OK, Check
^ Faulty light bulb.
^ Circuit 419 open.
^ Gage fuse blown. This will result in no oil or generator lights, seat belt reminder, etc.

Engine Cranks But Will Not Run, Check
^ Continuous battery - fuse or fusible link open.
^ ECM ignition fuse open.
^ Battery circuit 480 to ECM open.
^ Ignition circuit 439 to ECM open.
^ Poor connection to ECM.