Chart A-1 No Service Engine Soon Light

Fig. 011 - Wiring Diagram for Chart A-1 No "Service Engine Soon" Light. VIN 3, VIN 9:

CHART A-1, NO "SERVICE ENGINE SOON" LIGHT

There should always be a steady "SERVICE ENGINE SOON" Light when the ignition is "on" and engine stopped. Battery 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.

Fig. 010 - Chart A-1 - No "Service Engine Soon" Light:

1. No "SERVICE ENGINE SOON" Light suggests a faulty light bulb or open control circuit 419. Be sure test light is connected to 12 Volts when making check (1).

If the test light will not light, it indicates a possible battery supply problem to the ECM and would normally be related to an "Engine cranks but won't run" symptom.

2. and 3. These steps check for ignition and continuous battery voltages.

4. Solenoids are turned "ON" or "OFF" by the ECM internal electronic switches called" drivers". Each driver is part of a group of four called "Quad-Drivers". Failure of one can damage any other driver within the set.

Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "DRIVER". Using an ohmmeter, check the solenoid coil resistance of the following before installing a replacement ECM.
a. Canister Purge
b. A/C Relay
c. EGR Solenoid