Chrysler Repair: 99 41te - torque lockup cycles in/out only in warm weather, throttle position sensor, grand caravan

Question
1999 Grand Caravan, 3.3L, 41TE, 188K miles.

All through the winter, the transmission has shifted normally. As soon as the weather warmed up, I can hear engine rpm's rise and fall in 4th gear as the torque converter lockup goes in and out. Engine temperature gauge is normal, same in summer as in winter, right in the center. ATF is ATF+4, full flush last summer. The transmission has an extra Hayden cooler as well as the stock in radiator cooler. Ideas?


Answer
Hi Keith,
You might want to check the trans fluid level to start.
Then if you can get a fault code readout it would be good o verify that the only one detected was a P0740 which is the one for the tcc circuit. Autozone parts stores will do it for free. For example a P0841 (low/reverse pressure sensor switch) can be responsible.
Finally, you might want to check the throttle position sensor as that play a role in setting/cancelling the clutch. If it has a discontinuity in the region of 25-29 degrees it could cause that sort of problem. Just measure the resistance between the middle and either outside post of the sensor while you slowly change the throttle opening. It should vary smoothly. Finally pressure tests would reveal if something in the solenoid box was the cause.
You are basically trying to be sure that it isn't internal such as to require removal of the trans.
Roland