OVERHEATING TRANS/THM 700-R4 DRIVEN IN 4TH GEAR / TCC INOP

MODELS: LIGHT DUTY TRUCKS WITH THM 700-R4 TRANSMISSION

Some THM 7-00R4 transmissions may exhibit an overheating condition when the vehicle is driven in fourth gear (overdrive), and the torque converter clutch 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.

When diagnosing any THM 700-R4 transmission for an overheating condition, the following conditions are some possible causes:

1. The speedometer not working properly on E.C.M. controlled units.

2. A disconnected speedometer cable on E.C.M. controlled units.

3. The transmission electrical connector was disonnected.

4. The trorque converter clutch inoperative.

5. An inoperable E.C.M. unit.

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

To prevent possible transmission overheating conditions, it is recommended that the THM 7-00R4 transmission never be driven in fourth gear when the torque converter clutch is not operational. If the torque converter clutch is not operational or even suspected to be not operational, the vehicle should be driven in manual third range and the vehicle serviced.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.