Chart A-1 No Service Engine Soon Light

Chart A-1 - No "Service Engine Soon" Light:

Wiring Diagram For Chart A-1 - No "Service Engine Soon" Light:

CHART A-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. Ignition voltage 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. Battery feed CKT 840 is protected by a fusible link and is connected to the starter solenoid.

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. This will result in no oil, or generator lights, seat belt reminder, etc.
Engine cranks, but will not run.
^ Continuous battery - fuse or fusible link open
^ ECM ignition fuse open
^ Battery CKT 840 to ECM open
^ Ignition CKT 439 to ECM open
^ Poor connection to ECM