4l80e Lock Up Converter Trouble

Elk5012 · December 2, 2007

I have a problem with my torque converter unlocking while driving. When the trans is cold (under 120 degrees) it will lock up but when it reaches over 140 degrees it won't lock up. I took it to a trannie shop and it shows no codes. Sometimes it'll lock when warm at around 50 mph, but any more speed it won't stay locked. When cold it'll stay locked up at high speeds with no slipping. What can cause it to unlock when warmed up? I have never changed the fluid or filter but I don't pound the truck either, and the fluid looks and smells normal.

Genuinefine409 · December 2, 2007

I have a problem with my torque converter unlocking while driving. When the trans is cold (under 120 degrees) it will lock up but when it reaches over 140 degrees it won't lock up. I took it to a trannie shop and it shows no codes. Sometimes it'll lock when warm at around 50 mph, but any more speed it won't stay locked. When cold it'll stay locked up at high speeds with no slipping. What can cause it to unlock when warmed up? I have never changed the fluid or filter but I don't pound the truck either, and the fluid looks and smells normal.

I'm not 100% sure about this but If i remeber correctly there is a temp sensor and the convertor is supposed to not lock up until the trans is above a certain temp. and if it gets too hot it goes into hot mode and will keep the converter locked up. not 100% sure how it all works and what years it was on and if it was 4l60e or 4l80e but if you go to a good transmisson shop they should check it out for free. I know cottman does. They will be able to see on a scanner if the solonoid is going in and out or if its slipping or what. Depending on the year, they can also command the converter to lock up in any gear to see if something else is wrong.

Elk5012 · December 3, 2007

The trans shop had it all day and said the trans is fine. He said there is something telling the computer to unlock the converter, but still no codes. Could it be a map sensor thinking there is a load on the engine and unlocking it? Or maybe a vacuum leak? I'm stumped

sillyazz · December 4, 2007

The trans shop had it all day and said the trans is fine. He said there is something telling the computer to unlock the converter, but still no codes. Could it be a map sensor thinking there is a load on the engine and unlocking it? Or maybe a vacuum leak? I'm stumped

I think I would be taking it to a different tranny shop.

Genuinefine409 · December 4, 2007

Check your brake switch. When you press your brakes it unlocks the converter. I think there are 4 wires or so going to the brake switch but i'm not 100% bout that. in my old truck the trans went out and i got a local guy to rebuild it and after i got it back the converter wouldn't lock at all, he insisted it was my brake switch which the dealer and other trans shops said will keep the converter from locking up but it turned out he builds junk and my brake swtich was fine.

Elk5012 · December 4, 2007

This is the second trannie shop I've been to. The first said it needs a complete rebuild, but the trans shifts fine no shutter going into any of the gears, just unlocks while cruising. The second ran it all day with the scanner connected and said all is good and told me to go to an auto shop and see if there is anything, also he said it may need the computer flashed or maybe they can find a short that trips the lockup. I tried to hit the brakes while it is locked up (with the gas on) but that doesn't cause it to unlock.

Genuinefine409 · December 4, 2007

This is the second trannie shop I've been to. The first said it needs a complete rebuild, but the trans shifts fine no shutter going into any of the gears, just unlocks while cruising. The second ran it all day with the scanner connected and said all is good and told me to go to an auto shop and see if there is anything, also he said it may need the computer flashed or maybe they can find a short that trips the lockup. I tried to hit the brakes while it is locked up (with the gas on) but that doesn't cause it to unlock.

Not sure on how or what driving conditions it unlocks but i have a snap on scanner and while driving, like coasting down a hill, as soon has i press the brake pedal the TTC goes to disengaged on the scanner screen. I hope you can get your problem fixed with out getting a complete rebuild. I hade to pull the one in my old truck twice becuase of the first time it was put together right. It's no fun that for sure.

Elk5012 · December 28, 2007

Still not fixed. Took it for a road test the other day and went 40 miles at 69mph and it stayed locked. On the way back I took it up to 75mph and it unlocked after 1 mile and wouldn't lock up after that. Seems to be speed related but I can't figure this thing out.