Chart A-1 No Malfunction Indicator Lamp (MIL)

Chart A-1 No Malfunction Indicator Lamp (MIL) "Check Engine":

Malfunction Indicator Lamp Wiring Circuit:

Circuit Description:
There should always be a steady MIL (Check Engine) when the ignition is "ON" and engine stopped. Battery voltage is supplied directly to the light bulb. The Engine Control Module (ECM) will control the lamp and turn it "ON" by providing a ground path through CKT 419 to the ECM.

Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test will provide a ground path for the MIL (Check Engine) circuit. If the MIL (Check Engine) is "ON," then the external circuit is OK.
2. If CKTs 439 and 2 have voltage, the ECM grounds or the ECM is faulty.
3. Using a test light connected to B+. probe each of the system ground circuits to be sure a good ground is present. Refer to "ECM Connector End View" in front of this section for ECM pin locations of ground circuits.
4. If a fusible link or fuse is blown, be sure to consider branch circuits and splices to other components.

Diagnostic Aids:
Engine runs OK, check:
^ Faulty light bulb.
^ CKT 419 open.
^ Gauges fuse blown. This will result in no oil or generator lights, seat belt reminder. etc. Refer to "Fuse Block Details." which shows other branch circuits that are protected by the gauges fuse.

Engine cranks, but will not run:
^ ECM fuse open.
^ Battery CKT 2 to ECM open.
^ Ignition CKT 439 to ECM open.
^ Poor connection to ECM.
^ Fusible link open.