Chart A-1 No Service Engine Soon/Trans Light

No Service Engine Soon/Trans Light Chart A-1:

Circuit Description:
There should always be a steady 'Service Engine Soon" or "Trans" light with the ignition "ON" and engine stopped. Switched battery voltage is supplied to the light bulb. The PCM/TCM will control the light and turn it "ON" by providing a ground path through CKT 419 or CKT 1234.

Chart A-1 Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the ECM-B fuse is blown, refer to complete wiring 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.


Diagnostic Aids:
If the engine runs OK, check:
- Faulty light bulb.
- CKT 419 open.
- Gauges fuse blown. This will result in no brake warning light, oil or generator lights, seat belt reminder, etc.

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