Cayenne Gearbox issues, is a valve body the solution?

[tasporsche]

I recently purchased a high-mileage 2004 Cayenne Turbo. After a few small jobs including replacing the PCV diaphragm the car isn't in too bad a shape.

The only urgent issue which I knew about when purchasing is that there is a gearbox issue, which is quite typical of these 1st gen Cayennes. The symptoms it shows occur once the transmission fluid has had some time to warm up, after which point it starts having very hard shifts, particularly from 2nd to 3rd where the gearbox seems to disengage and the revs rise before a massive bang when it finally shifts to third. After this happening a couple of times the gearbox locks itself into 5th and you can't shift into any other gear. The only way to solve this is by turning the engine off and then starting it again, then the gearbox will select other gears. Also, it never seems to engage 1st and always starts in 2nd.

The reputation of these first-gen Cayennes and Aisin-Warner gearboxes in general seems to point directly to the valve body being at fault, however I'm just wondering if it's potentially more than that and if the entire gearbox should be replaced? Prices for used gearboxes aren't all that bad, although if the valve body is the only thing that's causing issues I'd rather save the hassle of having to haul the gearbox out of the car. 

Having researched this issue a bit, it seems that there are two different valve bodies that were used in these cars, one with a pressure switch and one without. Is there any way to tell which mine is by the VIN without having to pull off the transmission pan and check manually?

 

[Peter M]

What is the condition of the fluid and how much debris is in the pan and the filter?

If it is all pretty clean (and you know the fluid and the filter hasn't been recently replaced) it would give some confidence just to replace the valve body or individual valve body components.

If it's all a bit mucky, throw the whole lot away unless they are particularly cheap to rebuild or you need a core unit for exchange.

I know you don't want to drop the pan but it usually quick and easy to do and may actually give you a hint on how best to proceed.

[tasporsche]

From what the previous owner told me, he'd already had a shop do a flush and change the fluid to no avail. This stacks up as the trans pan drain plug looks very new. Seems like I might have to change the fluid again though to figure out what model valve body mine has.