OD/Off Indicator Does Not Light

Circuit Description
When the ignition switch turns ON, the Powertrain Control Module (PCM) performs a 3-second OD/OFF indicator bulb check. The PCM performs the bulb check by grounding the OD/OFF indicator control circuit. The OD switch button grounds the OD/OFF signal circuit to the PCM when the OD switch button releases. The above condition causes the PCM to ground the OD/OFF indicator control circuit. Grounding the OD/OFF indicator control circuit turns on the OD/OFF indicator lamp located in the instrument panel gauge cluster. The OD/OFF indicator informs the driver that the transmission will not shift into overdrive (4th gear).

The following conditions occur after the OD switch button is pressed:
1. The depressed OD switch button removes a path to ground to the OD/OFF signal circuit.
2. The PCM turns off the OD/OFF indicator lamp.
3. The PCM adds overdrive (4th gear) to the shift schedule.

Diagnostic Aids
Inspect for the following conditions:
^ An open OD/OFF indicator lamp bulb filament
^ An open IG Fuse
^ A faulty overdrive switch (always open)
^ A reduced ground (G201)
^ An open circuit between the PCM and the instrument panel gauge cluster
^ A damaged instrument panel gauge cluster printed circuit
^ A faulty PCM

The following conditions may cause an intermittent condition:
^ A reduced connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation.

Before replacing components, inspect the inline harness connector terminals for the following conditions:
^ Reduced connections
^ Backed out terminals
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Reduced terminal-to-wire connections Repeat the Powertrain OBD System Check after making repairs in order to ensure that the system functions normally.

Test Description
The numbers below refer to the step numbers on this diagnostic table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. The scan tool creates an electronic copy of the data taken when the fault occurred. The information then stores in the scan tool for later reference.
2. This step is to verify that the scan tool can read PCM input information from the overdrive switch.
3. This step tests for a faulty PCM.
4. This step inspects for an open bulb filament.
5. This step tests the power source to the instrument panel gauge cluster.
6. This step tests for an open in the indicator control circuit.
7. This step verifies if the PCM responds by turning on the O/D OFF indicator when grounding the O/D OFF signal circuit.
8. This step tests for a reduced ground (G201) to the overdrive switch.
9. This step tests for an open in the O/D OFF signal circuit.
10. This step tests for a faulty OD switch.
11. This step tests if the condition relates to a poor connection and is not due to a faulty PCM.
18. This step tests for proper operation of the O/D OFF indicator.