2003 1500HD Torque converter unlocking

[Graveyard Shift]

I've been having this problem intermitently for about a month. Going down the highway at 70 mph or so, the t/c would unlock and rpms

would jump up. Any little bit of throttle input would rev the engine way up. After 5-10 miles it would lock back up and be fine. Two weeks

ago it started unlocking after a mile or so and would not lock back up.

 

I tried all sorts of things to lock it back up, full throttle rev, then down... Hit the towing button, turned off tow mode... Neutral coast...

Slow back down to below 50 mph, then back up to speed... Neutral rev up.... Slow to 50, drop to 3rd gear, then back to OD and

speed back up...

 

None of these worked.

 

Had it in to a dealer 4 days ago and they changed the tcc, which supposedly locks and unlocks the t/c. They also did a fluid and filter

on the transmission. The truck behaved great for two days. Yesterday it did the unlock / lock thing. Today it did the unlock and stay

unlocked thing.

 

I'm at a loss here. This is not helping my mileage and gas is pretty pricey up here in Canada.

 

What else could this be, and how do I diagnose it without just throwing parts at it?

 

Thanks for any help,

Mark N.

[8.1HD/ALLISON]

Take it back to the dealer and tell them they did not fix the issue. Sounds like something electrical going on maybe? You could try ohming the wires from the ecm to the trans on the tcc solenoid circuit and make sure they are ok. Make sure to wiggle the harness around a bit if you do.

[gmtech4]

+1

 

take it back,

[jwilley]

My 02 2500hd started the same problem yesterday at 60mph while taking my son out of state for surgery. I was able to get a parts store to check the codes but only came up with a knock sensor/ no tranny codes. They cleared the computer and I was able to make it about 150 miles before it did it again today on the way home from the hospital. Made it to another parts store and had them clear the computer codes again and made it home. But have no clues what the problem is. If you solve this issue please post your solution.

[Graveyard Shift]

Ok, I finally got the truck back in to the dealership. Been really busy with the kids extracurricular stuff.

 

The tech of course couldn't get it to happen and everything checked out OK. He agreed though that

the 3-4 shift seemed to be hanging on 3rd a little too long. He said he found an update for the PCM

after a little research and applied it. So far so good. All shift points seem to be firmer and the t/c seem

to be locking and unlocking as it should. I tried all the things that used to mess it up and it was working

properly.

 

We shall see. I'll need it working right in a month and a half when I start towing my Jeep into the woods

again. I'd hate to have the tranny acting up with my trailer and Jeep on the hook on a fire road.

 

I'll update this if anything becomes new.

 

Mark N.