Chart A-1 No Service Engine Soon Light

Fig. 006 Chart A-1 - No "Service Engine Soon" Light:

Fig. 007 - Wiring Diagram for Chart A-1 No "Service Engine Soon" Light. VIN O, VIN 2, VIN R:

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 voltage is supplied to the light bulb. The Electronic Control Module (ECM) will turn the light on by grounding circuit 419 at the ECM.



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, there may be a battery supply problem to the ECM. This would normally be 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, using internal electronic switches called "drivers". Each driver is part of a group of four, called "Quad-Drivers". Failure of one driver can damage any other driver in 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 coil resistance of the following solenoids before replacing the ECM.
a. TCC Solenoid
b. A/C Relay
c. Fan Relay