Malfunction Indicator Lamp: Testing and Inspection

Chart A-1:

No "Service Engine Soon" Light, ALDL Or Won't Flash Code 12:

CIRCUIT DESCRIPTION:

There should always be a steady "SERVICE ENGINE SOON" (SES) 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. If the fuse in holder is blown refer to wiring diagram of Code 54 for complete circuit.

2. Using a test light connected to 12 volts probe each of the system ground circuits to be sure a good ground is present See SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC DIAGRAMS/ECM CONNECTOR IDENTIFICATION for ECM pin locations of ground circuits. A faulty ECM or a faulty or incorrect Mem-Cal may also be the cause.


DIAGNOSTIC AIDS:

Engine runs OK, check:

^ Faulty light bulb.
^ CKT 419 open.
^ Gage fuse blown. This will result in no oil or generator lights, seat belt reminder, etc.

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.