4l60e/241 trying to kill me in 4WD WTF is wrong?

[Nughuffer]

My stock 95 Tahoe 350TBI 4l60e/241 188k miles developed a weird issue last night. We got some decent snow here in the south so I had been out in it all day playing, 90% of which was in 4WD. I wasn't beating it but just riding in the woods to various sledding hills and pulling people on snowboards behind it. Ran fine all day. On the way home it started acting up. When I start from a stop it goes through 1st normally shifts briefly into 2nd then straight to OD lockup. So I'm running like 700 RPM at 25 mph valves ringing etc.. and it wont shift out unless I physically pull the lever out of OD. Same thing goes for when the shifter is in 3 except it goes into 3rd lockup at 15mph. When I put the shifter into 1 and try to descend a steep hill at idle it shifts to 2nd at around 1400 RPM. This only happens in 4WD and it got pretty dangerous trying to descend a long steep icy hill this morning with the ABS basically working against me. In 2WD it shifts through all gears fine and acts normally. I haven't tried this in low range but I'm going to assume its the same situation..

I'm no trans guy, so what the hell is going on? Where do I start troubleshooting? Is this a trans issue or a transfer case problem? Maybe some sort of sensor? Hell I have no clue. The fluid isn't burnt, is full and there hasn't been any sign of tranny/TC issues prior to yesterday night. No SES light either. I did a search but its not pulling up anything nor do I really know what to search for. This is my DD and its stock other than a small lift and 33" BFG MT's. Trans was replaced with a Jasper reman unit about 40k ago. Anybody have any ideas on where to start with this? Thanks

[Nughuffer]

Nobody?

[86k30]

trans temp is reading too high. Ecm sees this condition and forces lockup to cool the trans off. So the question is, is the trans actually hot or is their a wiring issue?? Get a diagnostic tool ( not the fawking local vatozone "scan"), 4l60e has a trans temp sensor built in that a diagnostic tool will be able to read the temp on. Start the vehicle cold and monitor the temp as you drive it. Should rise about the same rate as the engine temp give or take a few degrees. If you see a high temp right off or a bunch of spikes it is likely the temp sensor in the trans(which is built into the pressure switch manifold). Post up your findings or PM me. Jim

[jonechen]

enjoy here
thanks fpr your post

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Cold Case DVD 1-7

[1GMC4x4]

That was my first guess, that is was going into some kind of Limp home mode.

[Nughuffer]

Dont have access to a diagnostic tool just yet but I did fire it up this morning and immediately take off in 4wd and it still did the same thing. Ill look into the temp sensor. What I dont understand is I can run WOT in 2 wheel and it works fine.

[86k30]

Ecm changes some parameters when the 4wd is engaged. I don't know all of them, but it definetly affects lockup and speed sensor signals. Check the temp sensor readings to the actual temp via a infared temp gun or some kind of thermometer.

[g-wizz]

if its in limp home mode it probably isnt in OD.

[86k30]

z

[Nughuffer]

Where can I find a diagnostic tool short of paying a dealership $100 to look at it?

[r0nin89]

A snappy scanner could read that.

The only other issue I can think of that would happen in 4wd but not 2wd would be some sort of seriously out of limits difference between your input speed sensor and output speed sensor when in 4wd.

[Nughuffer]

Originally Posted by r0nin89

A snappy scanner could read that.

The only other issue I can think of that would happen in 4wd but not 2wd would be some sort of seriously out of limits difference between your input speed sensor and output speed sensor when in 4wd.

Where are these sensors located and how do I test them?

[Greg Ducato]

This trans only has an output speed sensor no input on the 4L60E. The sensor is located on the tail end of the transfer case and also supplies speed signal for the speedometer. How is that working? You may have a TPS issue causing the trans to stack gears and lockup. Really it is a total crapshoot without a diagnostic or other tools to help track the sensor/wiring/computer/trans problem down. Even a free diagnosis fro autozone should get a code reading if there are any stored and give you some notion of where to start. Short of that, try a good trans shop. You may have to pay a little for an expert diagnosis but it may be cheaper than changing parts till you get it right.

[Nughuffer]

Speedo works fine in 2wd. Ill check 4wd tomorrow but to my knowledge it was working fine because I was monitoring my speed on the interstate while in 4wd. I have a cheapy code reader that I will try and use. Is the speedo electric or cable operated? There is still 3 or 4" of ice on my driveway so I haven't really gotten under it to check it out but will post up if I find anything unusual tomorrow. The E brake light started coming on today and I had to pump the brakes to get pedal and then it would go off. Seems like I'm losing vacuum or something. It doesn't seem like these are related but who knows. This thing has been a real pile as of late. Thanks for the help all.

[rayfin interiors]

This may sound weird but shut the engine off, mash the gas pedal to the floor and hold it for a couple seconds. Then let off the gas and start it normally and try it.

There is a valve in the trans that sticks sometimes. My brother had me try that once and it worked. He was a mechanic at a large chevy dealership. WORTH A SHOT.

[86k30]

^^^ this is useless on a 93- up 4L60e. The sticking valve you are refering to is the throttle valve, and 4l60Es do not have this valve. Its got to be a temp sensor thing with the lockup symptoms.

[Nughuffer]

No codes set, nothing looks out of sorts and the speedo works the same in 2wd as 4wd. I dont have a temp gun or gauge so I guess Im going to have to pay somebody to diagnose this pile. It doesn't seem overly warm at operating temps, even so it still goes into lockup when its cold.

[Nughuffer]

Just drove it around for an hour on the street in 4wd and it didnt do it once.. maybe the snow>pavement>snow was messing with it and getting it hot. Who knows..