Hi. I am having a major issue with my trans and was hoping that someone on here could give me some insight. When I drive it on the highway, my converter locks up as it should. After driving for a little bit, the converter stops locking up. The RPM's stay high, and the trans temp goes up to about 200 F. Once I get off the highway, my truck slams into 2nd and 3rd. I actually dropped the trans pan today and replaced the lockup solenoid with the updated white one. The one that I removed was brown and appeared to be cracked. This did not fix the problem that I am having. There was actually a GM bulletin about replacing this solenoid for this problem.

I am at a loss here, and I am hoping somebody can help me, because I am going nuts

 

Ideally you need tuning software. That would really help you out. If anyone is local to you, you should find out if they can log your vehicle for you. For example with EFI live, you can command the PCM to lockup the torque converter clutch. If you do this and it works, then it sounds like your issue is not mechanical. Based on your symptoms though, it sounds likely something wrong with the trans or torque converter. Maybe your trans pump is on the way out. Maybe the torque converter clutch is slipping.

 

I thought about the clutch in the converter slipping, but I called circle d and they said whenever converter clutches slip, there would be metal in the trans pan. I had the pan down today, and there was no signs of any metal. I' m going to drive the truck with the scanner on it tomorrow ant see if I can command the lockup.

 

If the computer detects any misfires it will unlock the converter. Odd it only happens on the highway though. Im guesing there are no codes being thrown?

 

Only codes have been P0741 and P0894. I'm wondering about the misfire thing. Circle D was telling me that certain engine issues can tell the converter to unlock, just like you're saying. I will check with the scanner tomorrow.

 

What was the fix??? I'm having the same issue..

 

i have a p0741 trying to see if anyone on here ever figured it out im running a 4l80 with a harness form pcm of nc having tcc lockup problems