Chart A-1 No Service Engine Soon Light

Flowchart A1-1:

Chart A1-1 No "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 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 (CKT) 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 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. See ECM terminal end view in front of this section for ECM pin locations of ground circuits.

DIAGNOSTIC AIDS
Engine runs OK, check:

^ Faulty light bulb.
^ CKT 419 open.
^ Gage fuse blown.

Engine cranks but will not run:

^ Continuous battery - fuse or fusible link open.
^ ECM ignition fuse open.
^ Battery CKT 340 to ECM open.
^ Ignition CKT 439 to ECM open.
^ Poor connection to ECM.