Overdrive Off Indicator Always On. Chevrolet Joy 2008

For 1990-2009 cars

### Circuit Description

Within the ignition switch in the ON position, voltage is applied to the O/D switch. Whenever the overdrive switch, located next to the shifter; is depressed (switch contacts closed), system voltage is applied through the closed contacts of the overdrive switch to the TCM and the O/D lamp. When this occurs, the OD/OFF indicator light in the instrument Cluster will illuminate and the transmission control module (TCM) will simultaneously receive a voltage signal at the O/D input. With a voltage input, the TCM will disable the overdrive function. When the overdrive switch is depressed again, the overdrive switch opens. When this occurs, the O/D/OFF indicator light in the instrument cluster will go out and the voltage signal to the TCM O/D input will be removed. With a high voltage input, the TCM will disable the overdrive function and the transaxle will not be permitted to shift into overdrive.

### Diagnostic Aids

Inspect for the following conditions:

• | Poor connections at the component

• | Poor connections at any in line harness connectors

• | A faulty TCM

An intermittent may be caused by the following conditions:

• | A poor connection

• | Rubbed through wire insulation

Inspect the TCM harness connectors for the following conditions:

• | Backed out terminals

• | Improper mating

• | Broken locks

• | Improperly formed or damaged terminals

• | Poor terminal-to-wire connections

Inspect the wiring. If any wiring repairs are necessary, refer to Wiring Repairs .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step checks whether the condition is caused by a short to voltage or a constantly closed overdrive switch and not due to a faulty TCM.

2. This step checks whether the condition is caused by a faulty O/D OFF switch.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Automatic Transmission Controls Schematics
1 | Did you perform the Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Automatic Transmission

2

1. Press the overdrive switch to the up position (contacts open).
2. Turn the ignition switch to LOCK.
3. Disconnect the transmission control module (TCM) connector.
4. Turn ON the ignition, with the engine OFF.

Did the O/D OFF indicator illuminate?

Go to Step 3

Go to Step 6

3

1. Turn the ignition switch to LOCK.
2. Connect a test lamp between ground and TCM harness connector terminal 18.
3. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step 4

Go to Step 5

4 | With the test lamp still connected to the TCM connector, disconnect the overdrive switch. Does the test lamp illuminate? | Go to Step 5 | Go to Step 7
5 | Repair the short to voltage in the wire between the TCM and the Instrument Panel (I/P) cluster, or between the overdrive switch and TCM. Did you complete the repair? | Go to Step 9 | --
6 | Replace the TCM. Refer to Transmission Control Module Replacement . Did you complete the replacement? | Go to Step 9 | --
7 | Replace the overdrive switch. Did you complete the replacement? | Go to Step 9 | --
8 | Replace the instrument panel cluster (IPC). Refer to Instrument Cluster Replacement . Did you complete the replacement? | Go to Step 9 | --

9

1. Turn the ignition switch to LOCK.
2. Reconnect all disconnected connectors.
3. Press the overdrive switch to the up position (contacts open).
4. Turn ON the ignition, with the engine OFF.

Does the O/D OFF indicator light stay OFF?

System OK

Go to Step 2