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 PCM dims the OD/OFF indicator lamp by adding additional internal resistance to the OD/OFF indicator control output circuit when both of the following conditions occur:
| • | The OD/OFF indicator remains on. |
| • | The parking lamps/headlamp remain on. |
Dimming the OD/OFF indicator lamp reduces excessive glare to the driver at night. The following conditions occur after the OD switch button is pressed:
- The depressed OD switch button removes a path to ground to the OD/OFF signal circuit.
- The PCM turns off the OD/OFF indicator lamp.
- The PCM adds overdrive (4th gear) to the shift schedule.
Diagnostic Aids
Inspect for the following conditions:
| • | A short to ground in the OD/OFF indicator control |
| • | A short to ground in the OD switch signal between the OD switch and the PCM |
| • | A faulty OD switch (remaining closed at all times) |
| • | A faulty PCM |
Rubbed through wire insulation may cause an intermittent condition. Repeat the Powertrain OBD System Check after making repairs in order to ensure that the system functions normally.
Refer to Wiring Repairs in Wiring Systems when repairing any wiring.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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.
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This step tests for a short to ground in the OD/OFF indicator circuit.
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This step verifies the following conditions:
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This step verifies the following conditions:
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This step tests for proper operation of the OD/OFF indicator.
| • | A short to ground or a constantly-closed OD switch causes the condition. |
| • | A faulty PCM does not cause the condition. |
| • | A short to ground in the OD/OFF switch signal circuit causes the condition. |
| • | A faulty OD switch does not cause the condition. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls | ||
Does the OD/OFF indicator lamp turn on? | -- | |||
Does the test lamp turn on? | -- | |||
Does the test lamp turn on? | -- | |||
5 | Repair the short to ground in the WHT/BLK wire between the PCM and the instrument panel gauge cluster. Is the repair complete? | -- | -- | |
6 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls Is the procedure complete? | -- | -- | |
7 | Replace the OD switch. Refer to O/D Cut Switch Replacement . Is the procedure complete? | -- | -- | |
8 | Repair the short to ground in the ORN/GRN wire between the OD switch and the PCM. Is the repair complete? | -- | -- | |
Does the OD/OFF indicator lamp turn on for approximately 3 seconds? (The indicator will remain ON with the OD switch released.) | -- | System OK |
