Chart A-1 No Service Engine Soon Light

Chart A-1 - No "Service Engine Soon" Light:

Wiring Diagram for "Service Engine Soon" Light:

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. 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 CKT 419 to the ECM.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. No "Service Engine Soon" light suggests a faulty light bulb or open control CKT 419. Be sure test light is connected to 12 volts, when making check (1).

If 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. & 3. These steps check for ignition and continuous battery voltages.


4. Solenoids and relays 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. See CHART C-1.