Chart A-1 No Service Engine Soon Light

CIRCUIT DESCRIPTION
There should always be a steady "Check Engine" 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.

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 340 to ECM open.
^ Ignition CKT 439 to ECM open.
^ Poor connection to ECM

CHART TEST DESCRIPTION
1. If wiring and bulb check OK, reconnect ECM to see if Check Engine light comes on. If light is still out, it is a faulty ECM.

Before replacing ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM. See ECM wiring diagram for the solenoid(s) and relay(s) and the coil terminal identification.

When checking TCC solenoid, be sure to raise drive wheels and run above 30 MPH to close third gear apply switch.