With 4L60-E Automatic Transmission

Chart A-1 - PCM:

DLC Circuit PCM:

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

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the fuse/fusible link is blown, refer to control module wiring diagram 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. Refer to control module terminal end view in this section for control module pin locations of ground circuits.

DIAGNOSTIC AIDS
If the engine runs 0K, check:

^ Faulty light bulb
^ CKT 419 open, shorted to ground or blown fuse
^ Gauges 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 run, check:

^ Continuous battery-fuse or fusible link open.
^ Battery CKT 440 to fuel pump relay open.