tibi

I have a 2007 grand cherokee diesel, the trnsmission slips in very cold weather .The transmission was just serviced and did not solve the problem, ant suggestions on the root cause .

dave1123

How cold is cold? Try letting it warm up a bit.

tibi

it's slips when its below -10C, and the vehilce is warmed up ~ for 10 mins or longer.

dave1123

Okay, here's the thing. The transmission is warmed by the trans cooler in the radiator. If the engine isn't warm enough to start normal circulation of coolant through the radiator, the trans won't warm up. I would think a diesel should be up to temp in 10 minutes but I could be wrong. -10C is pretty fracking cold!

Okay, I've done what I could. Other people may have ideas.

NWhunter

My last Jeep was a 1994 Jeep Cherokee. I had the same problem, My transmission wouldn't go into 2nd when the jeep was cold. After busting the tranny appart I later found the 2nd gear clutch pack had gone out.

dave1123

Okay, but his is a 2007. I wouldn't think it's a clutch problem, but I'm just a humble old mechanic.

1ATony

Silly question, but on your 2007 do you need to check the fluid level with the tranny in neutral, and if so was that done?

It may read full in park but could be a quart low if your suppost to check it in neutral. It may tell you right on the dipstick my 97 does.

I had no idea I was suppost to check the level in neutral on my application.

Hope this helps you out. Just wanted to make sure you were reading it the right way.

ct67_72

Im not that familiar with the diesel. Does this use a Mercedes 722.x? trans?
How many miles are on it?
Also have you checked it for codes?

tibi

it has a w5j400 transmission, with 103,000 kms on it, and no codes show up .Once again it only slips in cold weather especially on inclines, and the vehicle is warmed up, works fine in mild temps(above-10c ).

ct67_72

Thats aMercedes 722.6. Thats just what chrysler calls it. Go under the jeep and on the pass side front look at the case connector. (electrical connector for transmission) It passes through the case to the harness that attaches to all the solenoids and trans temp sensor on the valve body.
It is a 1/4 turn connector. Unplug it and check inside the connector ends for fluid.
The connectors are notorious for leaking and the fluid will short the internal harness and make them do funny things.
Check this first. If its wet, clean it with good electrical contact cleaner and put some dialectric grease in there.
Beyond that, see if you can get access to a scanner that has diagnostic info. Get trans data and see what the trans temp is reading. The sensors are also notoriously bad. Im sure it could affect its performance.
These are pretty good units, usually not too much that goes wrong internally. Not to say I havent seen any bad, but not too much.

ct67_72

Also, when its slipping, try and manually downshift it to first gear and see if it still slips, maybe trying to take off in second.

tibi

Thanks, I shall check it out ,and for the slipping it goes into neutral, you pull over and put into park, thats if it holds, if not foot on brake , rev it for a few minutes and then you can drive, biut when it was -30c here it took 15 min for the tranny oil to warm up and limp home, and this was after the service.Going back to the dealership, but I have my doubts with their expertise on Jeep Diesels.Any help in troubleshotting is very much appreciated!