Hi Everyone! I just bought a "2005 Volvo s40 T5 AWD Automatic" with 175,000 miles from a private party, and it appears to have transmission problems when warm, but I was told my transmission is OK by AAMCO. So let me tell you exactly whats happening.

*** Note - All of what I'm explaining below is city driving. Highway gives same problems but they start to occur a bit earlier than driving in the city.

When driving the vehicle after it hasn't been used for a few hours, the transmission runs great! No rough shifts and no slips. After driving the vehicle for about 15-25 minutes, the transmission starts to progressively shift harder, and harder. At about 25-35 minutes, the transmission starts to slip in addition to the rough shifts. When I say slip, I mean that when the transmission starts to change the gear, it goes into "neutral" and the engine revs skyrocket. about 3-6 seconds later, the transmission finally finishes changing the gear, very very roughly. After 30-40 minutes, the car becomes ridiculously difficult to drive. The gears are slipping very often and shifts are super rough.

If I let the car cool down for a few hours, all returns back to normal until the car heats up again.

I brought the car to a local "AAMCO Transmissions" for a diagnostics, and to my surprise, they said that there was no problem with the transmission. They said they drove it around town, and the transmission worked fine. They also said they checked the fluids, error codes, etc, and it all came back normal.

The reason AAMCO probably didn't experience any transmission issues while test driving the car is because they didn't drive it long enough. I told them that and they still insisted that there is nothing wrong with the transmission and that it might be something other than the transmission causing the issues.

They gave me a Vehicle Record Report, and it had the following error codes.

Central Electronic Module Passenger Junction Box B Codes
* 6F51 Tail gate handle Faulty signal
All System Codes
* 400C Three - Way Catalytic Converter (TWC) Efficiency, Bank 1
* 6F51 Tail gate handle Faulty signal

My personal ODBII adapter gave me an error code of "P0420 - Catalyst System Efficiency Below Threshold (Bank 1)".

At this point, I have no clue what to do. I checked the transmission fluid via the dipstick and its dark brown, but there are no visible debris. Could it be as simple as a transmission fluid change/flush? Any help would be greatly appreciated! Thanks is advance!

 

the 400C and P0420 are telling you the same thing - the variance between the front and rear O2 sensors is out of range. Could be a sensor, could be the cat, could be an air leak or vacuum leak or weak plugs/coils making the front sensor work too hard... As far as the transmission slipping when warm goes, that may not generate a fault code. A flush or drain/fill can't hurt, particularly if the fluid is dark or brown. Pull the transmission dipstick and wipe on a white paper towel. If black, you probably already have burnt stuff so you would need to drop the pan and clean it out. If brownish, you can do a drain fill and get the oil viscosity to the appropriate weight. If reddish black, you have good fluid, which suggests somebody may have already done a flush - and may have used the wrong fluid for your model (some Volvos use Mercon, others use JWS 3309, check your model/owners manual to be sure).

 

5 speed use JWS3309 spec'd.

 

This is an older post, but hoping you were able to resolve the issue! @volvo3846 any luck? I'm having the same problem and have been told by transmissions shops that everything is OK and that it doesn't harm the vehicle to drive it like that. I just can't stand it and would like to fix it.

 

Sounds an awful lot like shift solenoids. Even so, if I bought a car with that kind of issue (hey wait... I did!) I'd do a transmission fluid drain-and-fill, and would add 12 ounces of LubeGard Platinum (had good luck with it in several cars). Make sure you get the level right - but since Volvo makes it nearly impossible to get to the tranny fluid dipstick with the engine warm and the car parked level, the smart way is to just drain it and put four quarts back in (I've been told by a very experienced pro Volvo mech that will come out just right). You can reduce the fluid by 12 ounce if you do use the LubeGard.

If that doesn't work (and there's a good chance it will...) then I'd suggest swapping out the shift solenoids. Not really a terribly difficult job, though it's not for every DIYer. I did a short video showing the process: