Question2005 Jetta GL TDI wagon. 53k miles. I have a TDI-only business. Picked this car up in NC and drive home to VT. When cruise is on, set at let's say 70 or 65, when heading up grade, transmission starts to get into a pattern with shifting down but only staying there for 2 seconds. Even after cresting hill, will keep hunting for a while. No cruise, no problem. Or, if pushed into manual mode, no issue.
Have appointment for VW, but in phone call to my service guys, they can find no VW notices of such problem and they have no idea up front.
Software / flash needs updating?
Will appreciate anything to look for.
AnswerHi Dale;
Thanks for the detail, and a little elaboration. Automatic transmissions in diesel powered cars, or trucks...no matter who the manufacturer is....have a problem with electronically controlled transmissions in these driving conditions. In the old days, the transmission was shifted when the engine vacuum was enough to pull on a diaphragm in the "vacuum modulator." (This was one of the secret weapons of the Martian in bugs bunny cartoons, but they are , or rather were a real transmission part.) If the vacuum decrease to a certain threshold, due to the throttle opening far enough to allow the intake manifold to approach atmospheric pressure, the transmission would downshift. The electronically controlled transmission doesn't even consult engine vacuum. It looks at vehicle speed, engine rpm, the torque converter lock up condition, and the output shaft speed. Other manufacturers are ahead of VW by a little bit in this arena, because they use a PCM, which is short for powertrain control module, but VW uses a separate ECM, and TCM...engine control module, and transmission control module. So the only thing the transmission control, and engine control share is the information pertaining to "engine load." At low rpm, diesels still make huge torque, so the transmission can stay in a higher gear than if the engine were gasoline. Once you add a hill to the mix, the engine load increases, so the "load" value goes up. Once that "load" value increases to a certain level, the downshift takes place. A reflash might help, but only one done at the dealer, because if there is any powertrain warranty left, it will not be affected by the factory reprogram. The only other thing I would recommend is have the transmission serviced....filter, pan gasket, and fluid...at the dealer only...it has to be done at a certain transmission fluid temperature, and only they have the special tools. A "service" is expensive, but worth it. A couple of hundred bucks now, will save thousands later. Fresh fluid flows more easily, and engages solenoids, steels, and clutches faster, and with less pump pressure, so the transmission will change it's behavior with that simple procedure. Beyond that however, if you still experience a gear hunt, just shift into drive, instead of overdrive. VW diesels will still yield excellent mileage, and they will still be able to run at a slightly elevated rpm range.. Good luck, Dale. I hope this helps.
