With Port Fuel Injection (PFI)

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

Wiring Diagram for "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. The Engine Control Module (ECM) will turn the light "ON" by grounding CKT 419 at the ECM.

Engine runs OK, check:

^ Faulty light bulb.

^ CKT 419 open.


^ Gage fuse blown. This will result in no stop lights, 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 240 to ECM open.

^ Ignition CKT 439 to ECM open.

^ Poor connection to ECM.

Diagnostic Aids:

Solenoids and relays are turned "ON" and "OFF" by the ECM, using internal electronic switches called "drivers." Each driver is part of a group of four called quad-drivers. Failure of one driver can damage any other driver in the set.

If the diagnostics indicate an ECM failure, see CHART C-1.