Chart A-1 No Service Engine Soon Light

Service Engine Soon Lamp Circuit Chart A-1:

Service Engine Soon Lamp Circuit:

Circuit Description:
There should always be a steady "Service Engine Soon" light when the ignition is "ON" and engine is stopped. Battery voltage is supplied to the light bulb. The PCM will control the light and turn it "ON" by providing a ground path through CKT 419 to the PCM.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step will isolate the problem in CKT 419.
2. If CKTs 440 and 439 have voltage, the PCM connections, grounds, or PCM is faulty.
3. Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is present. Refer to PCM terminal end view in this section for PCM pin locations of ground circuits.
4. If the fuse/fusible link is blown, refer to PCM wiring diagram for complete circuit.


Diagnostic Aids:
If the engine runs OK, check:
^ Faulty light bulb
^ CKT 419 open, shorted to ground or blown fuse.

If the engine cranks but will not run, check:
^ Continuous battery-fuse or fusible link open
^ PCM ignition fuse open
^ Battery CKT 440/340 to PCM open
^ Ignition CKT 439 to PCM open
^ Poor connection to PCM