Chart A-1 No Service Engine Soon Light

Chart A-1 No Malfunction Indicator Lamp (MIL) "Service Engine Soon":

On-Board Diagnostic (OBD) System Check:

CIRCUIT DESCRIPTION
There should always be a steady Malfunction Indicator Lamp (MIL) with the ignition "ON" and engine "OFF." Switched battery voltage is supplied to the lamp. The PCM/TCM will control the lamp and turn it "ON" by providing a ground path through CKT 419 or CKT 1234.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. If the ECM-B fuse is open, refer to "PCM or TCM wiring diagram" for complete circuit. Diagrams
2. Using a test light connected to 12 volts, probe each of the system ground circuits and check that a good ground is present.

DIAGNOSTIC AIDS
If the engine operates OK, check:
^ Faulty light bulb.
^ CKT 419/1234 open.
^ Gages fuse open. This will result in no brake warning light, oil or generator lights, seat belt reminder, etc.

If the engine cranks but will not operate, check:
^ Continuous battery ECM-B fuse open.
^ TCM Ignition In-Line fuse open.
^ Battery CKT 440 to PCM/TCM open.
^ Ignition CKT 439 to PCM/TCM open.
^ Poor connection to PCM/TCM.