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. Buttery ignition voltage is supplied to the light bulb. The ECM will control the light and turn it "ON" by providing a ground path through CKT 419.
Test Description : Numbers below refer to circled numbers on the diagnostic chart.
If the fuse in holder is blown, refer to facing page of Code 54 for complete circuit.
Using a test light connected to 12 volts, 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 :
If the engine runs 0K, 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.
If the engine cranks but will not run, check:
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.
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