Chart A1 - No "Service Engine Soon" Light: Notes

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. The electronic control module (ECM) will control the light and turn it on by providing a ground path through circuit No. 419 to the ECM.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Battery voltage at circuit No. 340 is protected by a 20-amp in-line fuse. If this fuse was blown, refer to wiring schematic for Code 54 test procedures.
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 this article.