Overdrive Unit Operation

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1995 Jeep Grand Cherokee, 1995 Dodge Ram Wagon, 1995 Dodge Ram Van, 1995 Dodge Pickup, and 1995 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

The 3-4 shift is electronically controlled and hydraulically activated by the Powertrain Control Module (PCM). PCM is located on passenger side of firewall on all models except AN body. On AN body, PCM is located on passenger side inner fender. Overdrive or 4th gear operation is controlled by a manually operated overdrive switch on the instrument panel. Overdrive switch is in the electrical circuit with overdrive solenoid on the valve body and PCM. Transmission will not shift into overdrive or 4th gear if switch is not in the ON position. When overdrive switch is in the OFF position, the overdrive switch overrides the PCM, preventing transmission from shifting into overdrive or 4th gear.

Overdrive switch contains an indicator light which activates when overdrive switch is in the OFF position. Overdrive switch will reset when ignition is turned off, allowing transmission to automatically shift into overdrive or 4th gear.

On Pickup applications with 5.9L Diesel engine, overdrive or 4th gear operation is also controlled by engine coolant temperature and transmission fluid temperature switches. Engine coolant temperature switch prevents transmission from shifting into overdrive or 4th gear when engine coolant temperature is less than 65°F (18°C). Transmission fluid temperature switch will either downshift transmission to 3rd gear or prevent a 3-4 upshift when transmission fluid temperature exceeds 270-275°F (132-135°C). Transmission fluid temperature switch is located in oil cooler outlet line, near the transmission case.

On Pickup applications with 5.9L Diesel engine and gasoline models with special auxiliary transmission oil cooler, overdrive or 4th gear operation is controlled by transmission fluid temperature sensor and the PCM. Transmission fluid temperature sensor is located in oil cooler outlet line, near the transmission case. Transmission fluid temperature sensor monitors transmission fluid temperature and is in the circuit with the overdrive solenoid on the valve body and the PCM.

NOTE: CNG powered vehicles are not equipped with transmission temperature sensor.

Transmission fluid temperature sensor prevents overdrive or 4th gear operation when transmission fluid temperature is less than 60°F (15°C). Transmission fluid temperature sensor will either downshift transmission to 3rd gear or prevent a 3-4 upshift when transmission fluid temperature exceeds 270-275°F (132-135°C).

On all models, the PCM controls overdrive solenoid, located on the valve body, using input signals from various sensors. Overdrive solenoid operation is monitored by the PCM. The PCM self-diagnostic system stores a diagnostic fault message in the memory in event of a malfunction. Diagnostic fault message can be retrieved for overdrive solenoid diagnosis. See SELF-DIAGNOSTIC SYSTEM .