GEARBOX TCU

[RS6Rottweiler]

I have an issue with my Gearbox which causes the box to jump into gear when selecting drive or reverse and when driven does not change gear but stays in a constant drive mode but it doesn't happen all the time? I am advised that the cause of this is the Gearbox TCU, there are no new ones available anyway with no lead time from Audi on availability? I see that there appears to be some available on ebay but you don't know what you are getting? Therefore, before I go and spend some money, I wondered if anyone has a spare Gearbox TCU who lives near Fife who would be willing to let me try it in my car to confirm that it is the TCU that is causing the fault, here's hoping??

[Shoppinit]

Fingers crossed you find one. It's an easy swap at least.

[Ben_r1]

If you have the budget and want it done properly try speaking to Audi UK and explain the situation, they may source one down for you in Germany.

[HPsauce]

What's the basis of the faulty TCU diagnosis; have you had a VCDS scan to see if the TCU is reporting anything?
Also could this actually be the F125 switch? Not such an easy swap, but available and cheaper.

[PipRS6]

I'm new to these cars but Auto boxes I have seen the past doing similar can sometimes be fixed with a simple oil change. If it hasn't been done in a while it is probably worth trying as it is probably the easier/cheapest/quickest solution. And if it doesn't work you haven't lost much.

[MeTsU]

I'm new to these cars but Auto boxes I have seen the past doing similar can sometimes be fixed with a simple oil change. If it hasn't been done in a while it is probably worth trying as it is probably the easier/cheapest/quickest solution. And if it doesn't work you haven't lost much.

If you were to go that route, it would be worth your while to replace the F125 switch then, as it's right there - dependant on it's cost of course.

[Shoppinit]

Yee-ess. Right there. Obviously you've never changed one. viewtopic.php?f=2&t=116756

[MeTsU]

Yee-ess. Right there. Obviously you've never changed one. viewtopic.php?f=2&t=116756

Yeah, read through the DIY, prior to purchasing my RS funnily - part of the homework.

I guess it's dependant if you have access to tool and a ramp of course - luckily I do, at a very very special price.

[Shoppinit]

It's typical of the way Audi designed this car. It would be a five minute job... if not for the fact that one bolt is ridiculously inaccessible. It's not for nothing that the procedure in the workshop manual starts "Remove the engine and gearbox..."

The OP swapping out the TCU to see if that resolves the problem is a fast way of eliminating, so that makes sense... if he can find one. F125 aren't cheap and a gearbox oil change isn't particularly cheap either. Smart diagnostics FTW.

What's the Vagcom say?

[MeTsU]

It's typical of the way Audi designed this car. It would be a five minute job... if not for the fact that one bolt is ridiculously inaccessible. It's not for nothing that the procedure in the workshop manual starts "Remove the engine and gearbox..."

The OP swapping out the TCU to see if that resolves the problem is a fast way of eliminating, so that makes sense... if he can find one. F125 aren't cheap and a gearbox oil change isn't particularly cheap either. Smart diagnostics FTW.

What's the Vagcom say?

Can't argue with that.

[RS6Rottweiler]

The gearbox has been serviced as per schedule with all correct oil and filter changes carried out, in fact i think they did an extra change to see if this made a difference. The TCU has been sent away for repair twice, first time they sent it back saying nothing wrong with it, so sent back to them and they still said that there was nothing wrong with it but it looked like they had been inside it this time and there was a notable difference in gearbox operation for a while but has since gone back to the way it was if not worse.

I could buy a TCU on ebay but if this is a common TCU issue then am I just buying another TCU that could fail at anytime? However, if one were actually available from Audi they were at the last check £907.55 plus VAT and fitting so not cheap if it turns out that the TCU is not actually the problem, hence why if it was possible to try another one and see if this made a difference before parting with my hard earned.

[Ajc]

I don't think the TCU's are particularly unreliable and common for failure . My money would be in a second hand one I think rather than stumping up for a new unit . If you get one from a reputable seller then you should have a 30 day warranty with it .

[HPsauce]

What's the Vagcom say?

This is absolutely the first thing to do (VCDS/Vagcom).
Scan it, note results, clear error codes, run it, scan again.
You say it doesn't happen all the time, so scan it again every "normal" run and definitely after it goes wrong.

If you don't have VCDS then buy a genuine lead! It's a lot cheaper than a new TCU.

You'll need a laptop too, but a cheap old one will be fine.

[Ben_r1]

I'm new to these cars but Auto boxes I have seen the past doing similar can sometimes be fixed with a simple oil change. If it hasn't been done in a while it is probably worth trying as it is probably the easier/cheapest/quickest solution. And if it doesn't work you haven't lost much.

The ‘proper’ Audi gearbox oil isn’t an absolute fortune! I wouldn’t be chucking it in for the sake of it.

[MeTsU]

I'm new to these cars but Auto boxes I have seen the past doing similar can sometimes be fixed with a simple oil change. If it hasn't been done in a while it is probably worth trying as it is probably the easier/cheapest/quickest solution. And if it doesn't work you haven't lost much.

The ‘proper’ Audi gearbox oil isn’t an absolute fortune! I wouldn’t be chucking it in for the sake of it.

I got a quote from Audi, and then from ZF directly for the oil when I did my new gearbox oil and filter. ZF was cheaper. So it's worthwhile trying them directly.