More Torque Converter Forensics 4L80-E Overheating/740 Codes

Try to imagine the difficult job tech line technicians have. They are asked to decipher bits and pieces of information that may or may not be accurate and then come up with the correct answer. The information the technicians collected for the following two scenarios seemed to be as different as night and day. The information even originated in different countries. The amazing thing about these different complaints and symptoms was that they all had the same root cause.

Vehicle #1

Vehicle #1 was a 1992 GM 3500 4 x 4 equipped with a utility body. The vehicle would not move forward and was towed to the shop. Upon tear down, the forward clutches were found to be completely burned up, and a complete overhaul including a rebuilt torque converter was recommended. The customer approved the overhaul and requested a temperature gauge be installed at the same time. The repair seemed to be progressing routinely until the R&R technician noticed that the temperature gauge had climbed to 190°F while the vehicle was still on the lift. At first the gauge was thought to be defective, but a replacement gauge showed the same temperature. The technician suspected a restricted cooler and a flow monitoring device was installed before the vehicle was road tested. On the shop’s usual 6-mile test loop, the vehicle had a good cooler flow rate of 3.2 gallons per minute (G.P.M.), but reached transmission temperatures in excess of 285°F. (Figure 1).

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Article No.: TCTIP-03-10
Author: Ed Lee
Total Pages: 2

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