A/T - Overheating In Fourth Gear

SIL 86-19 (Sept)

SUBJECT: 700 R4

PROBLEM: Overheating in fourth gear

Some THM 700 R4 transmissions may exhibit an over-heating condition when the vehicle is driven in fourth gear (overdrive), and the torque converter is not operational.

Under these conditions, and especially under heavy load conditions, heat is generated in the torque converter that the transmission cooler cannot cool adequately - even with an extra cooler installed.

CAUSES:

Possible causes of overheating on any THM 700 R4:

1. The speedometer not working properly, or the vehicle speed sensor (USS) on ECM controlled units.

2. Transmission electrical connector being disconnected.

3. The torque converter clutch inoperative.

4. Inoperable ECM unit

5. Poor engine performance

6. Inoperable solenoid and/or valve body switches.

7. Refer to the appropriate torque converter diagnosis section in your service manual for additional information.

CURE:

To prevent transmission overheating conditions, it is recommended that the THM 700 R4 never be driven in fourth gear when the torque converter clutch is not operational.

If the torque converter clutch is not operational, or if it is even suspected to be not operational, the vehicle should be driven in manual third range, and the vehicle serviced as soon as possible to correct the condition.