O/D Off Indicator Does Not Light

Diagnostic Chart:

Description:

Wiring Diagram:

Circuit Description

When the ignition switch is turned to the ON position, the Powertrain Control Module (PCM) performs a three second OD/OFF indicator bulb check by ground the OD/OFF indicator control circuit during such period. When the OD switch button is in the released position, it grounds the OD/OFF signal circuit to the PCM. This causes the PCM to ground the OD/OFF indicator control circuit, turning on the OD/OFF indicator lamp located in the I/P gage cluster. This indicator informs the driver that the transmission will not shift into overdrive (4th gear). When this indicator is on and parking lamps/headlamps are turned on, the PCM dims the OD/OFF indicator lamp by adding additional internal resistance to the OD/OFF indicator control output circuit. This reduces excessive glare to the driver from the OD/OFF indicator lamp at night. When the OD switch button is pressed, it removes a path to ground to the OD/OFF signal circuit. Then, the PCM turns off the OD/OFF indicator lamp and the PCM adds overdrive (4th gear) to the shift schedule.

Diagnostic Aids

Check for the following:

- Open OD/OFF indicator lamp bulb filament.

- Open IG COIL freeze.

- Faulty OD switch (always open).

- Poor ground (G200).

- Open circuit between the PCM and the I/P gage cluster.

- Damaged I/P gage cluster printed circuit.

- Faulty PCM.

An intermittent condition may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check for poor connections at component and inline harness connector terminal for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and for poor terminal-to-wire connections before replacing components. After repairs have been made, repeat the Powertrain OBD System Check to ensure the system is functioning normally.

If any wiring repairs need to be made, refer to Repair Procedures in Electrical Diagnosis.

Test Description

Numbers below refer to the circled numbers on the diagnostic chart.

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. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. Checks that PCM performs bulb check.

3. Checks integrity of the indicator control circuit.

4. Checks for an open bulb filament.

5. Checks power source to the I/P gage cluster.

6. Checks for an open in the indicator control circuit.

7. Checks if the PCM responds by turning on the OD/OFF indicator when grounding the ON/OFF signal circuit.

8. Checks for a poor ground (G200) to the OD switch.

9. Checks for a faulty OD switch.

10. Checks whether the condition is related to a poor connection and not due to a faulty PCM.

18. Checks for proper operation of the OD/OFF indicator.