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 transmission control module (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:
| • | Open fuse |
| • | Poor connections at any in line harness connectors |
| • | Loose ground connections |
An intermittent may be caused by the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
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.
-
This step checks the overdrive switch by jumping the switch to B+.
-
This step checks the lamp control circuit for an open circuit.
-
This step checks the O/D OFF indicator.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | |||
1 | Did you perform the Diagnostic System Check -- Vehicle? | Go to Step 2 | |
Did the O/D OFF indicator illuminate? | Go to Step 7 | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 6 | Go to Step 4 | |
Backprobe with 3A fused jumper between the instrument cluster connector at the lamp control circuit and B+. Does the test lamp illuminate? | Go to Step 5 | Go to Step 8 | |
5 | Repair an open circuit in the lamp control circuit. Refer to Wiring Repairs. Did you complete the repair? | Go to Step 9 | -- |
6 | Repair an open circuit in the switch ignition feed circuit. Refer to Wiring Repairs. | 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 |
Does the O/D OFF indicator light toggle from on to OFF. | System OK | Go to Step 2 |
