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. Battery 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 circuit 419 to the ECM.

If there is no "Service Engine Soon" light and engine runs, check:

^ Faulty light bulb.
^ CKT 419 open.
^ Gage fuse blown. This may result in no stop lights, oil or generator lights, seat belt reminder, etc.

If there is no "Service Engine Soon" light and "Engine Cranks But Will Not Run", check:

^ ECM B fuse open.
^ ECM I fuse open.
^ Battery CKT 440 to ECM open.
^ Ignition CKT 439 to ECM open.
^ Poor connection to ECM.


Test Description:

1. 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. Solenoid and relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "driver".


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.