Engine Control Module: Testing and Inspection

On-Board Diagnostic System Check:

On-Board Diagnostic System Check Wiring Circuit:

Circuit Description:

There should always be a steady MIL (Service Engine Soon) when the ignition is 'ON" and engine stopped. Battery voltage is supplied through the ignition switch directly to the lamp. The Engine Control Module (ECM) controls the lamp and turns it "ON" by providing a ground path through CKT 419 to the ECM.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the fusible link is blown, locate and repair short to ground.
2. Using a test light connected to 12 volts (B+) 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.
^ Gauges fuse blown; this will result in the loss of MIL, oil lamp, brake light, etc. on I/P.

Engine cranks but will not run.
^ Continuous battery - fuse or fusible link open.
^ ECM ignition fuse open.
^ Battery CKT 2 to ECM open.
^ Ignition CKT 639 to ECM open.
^ Poor connection to ECM.
^ Poor ECM ground.