Hey, my '01 Z28 is having an issue with its 4l60e trans. I have a trans cooler installed & Trans has 30K on it.

Whenever I'm in stop in go traffic for awhile...over 20 miles...the trans will start revving high before shifting. 3K for the 1-2 shift instead 1.5K. It'll also downshift harshly. It only does this when warm & I've been driving for quite awhile. Engine coolant temp never gets over 205. It won't do this on short trips around town or a blast down the highway in no traffic.

Any ideas? TPS sensor bad? Is it just low trans fluid level? I guess I should check the level first before anything.

 

Just checked the fluid level & it's perfect...fluid looks good too.

Does this mean it's the TPS sensor...maybe the torque converter is going bad? I feel like the line pressure just goes nuts if the car's been running in heavy traffic for awhile.

 

epc but could be a cross leak in the valve body and if line pressure is going crazy it's going in to max line because of a leak. is it happening when it's all warmed up in ran through the gears lock up mite be a problem in the converter might be slipping than it goes in to max line. superior makes a lock up valve for the pump 40% more oil to the converter make sure your not running sonnax valves in the valve body there junk they cross leak like crazy seen it a 100 times jasper transmissions use sonnax junk stay away.

 

If its shifting late without slipping, that would indicate the PCM is commanding the late shift, which is turn is likely due to an engine sensor problem, either the TPS or MAF.
Hook up a simple scanner and read the TPS position. With ignition on, engine off confirm the TPS reads between 0% to 95%+. A fancy scanner, like HP Tuners, can read the MAF frequency to diagnose the MAF too. A fancy scanner, which a trans shop will have, can also confirm that the PCM is commanding the late shifts.

 

The simple scanner I have shows throttle position at 0 - .4% with the ignition on & the engine off. It goes all the way to 100% & then back down to .4%.

When the engine is on, at first it shows 0 - .4%, but it slowly creeps up to .8%, & then after about 20 mins of driving in traffic, the lowest the throttle percentage gets to is 11.8%. This is with foot completely off the accelerator. Even measured it on Park as well...still 11.8%. Engine temp is never over 205°.

Does this look like a bad TPS?

 

11.8% TPS in a drive-by cable system is way too much; it should be below 1%.
New drive-by-wire system do read up to about 8% at idle because there is no IAC.

So, since I think your '01 Z28 is drive-by-cable, it does sound like a TPS or wiring issue.

 

Thanks, I'm gonna clean the throttle body & replace the TSP sensor then. See if that fixes things. I'll report back with my results.

 

Forgot to report back...A Throttle Body Clean & new TSP Sensor fixed everything! Thanks for all the help guys!