0B5 DSG/S-Tronic issues, I need to pick your brains.

[Macflurry26]

Hi guys, apologies for the novel as an opening post but I need some opinions on an ongoing fault and the next stage of repair. So please, bear with me.

My girlfriend has an 09 plate Q5. It was bought through a private sale and just after the gearbox malfunction lights started flashing up while driving which put the car into limp mode until the engine was restarted. Once restarted it would drive for either hours or minutes before coming back on.

I've sent the Mechatronic unit to ECU testing who gave it a clean bill of health, refitted it with fresh oil and a couple of days later same issues again. I've scoured the net previously and there is a wealth of info on this that says it's Mechatronic unit, wiring loom or clutch causing the issues but without proper diagnosis you can't say for certain.

We've taken the car to a mechanic that genuinely knows his stuff. So I have no doubt he knows what he is doing, but for the next part of the repairs there is something that doesn't add up to me and so I need to ask for peace of mind before putting even more money into what are already expensive repairs. I will discuss this with him before they go ahead but just in case I've overlooked something obvious I thought I'd throw this out on here before I go to him with it.

The fault codes on the car pointed to gear actuator 2 mechanical failure which resulted in the gear box being only able to select even numbered gears while the car drove in limp mode but drove fine once restarted until the warning light came back.

The car has already had the wiring loom in the box replaced as per Audis recommendation due to known failures and the issues it causes. It also had an actuatorunit replaced at the same time. The warning light still came back and so the car was booked in for a Mechatronic unit replacement.

The Mechatronic unit has been replaced and the car drove faultlessly for around a month. Although one thing I had noticed was that the car seemed slow to engage when moving from reverse to drive. Then on one of the days I tried to pull away before the gears had fully engaged and had the same light pop up with the same symptoms as before. Reset the engine and it drove fine. This happened a couple more times over the next week or two and then it happened again to my girlfriend as she pulled up to the end of our drive.

So, back it goes for a code read and gear selector 2 malfunction pops up. Performed a recalibration of the gear box and it drove fine all the way home. Next day my girlfriend goes to drop the dog off before work, but as she approached junctions the car cuts out on her with the gearbox warning light. After restarting it the light comes back on and she notices that once again she only has even numbered gears which would explain why it struggles at the junctions. Now after calling the garage they said to try and get back home using the paddles to shift gear but after that avoid driving it. So she managed to get back home with the paddles.

She got in touch with the mechanic who called back later that day and said he's been in touch with the technical department for the Mechatronic unit and they are saying it's the dual-clutch that is looking to be faulty. SO we've booked it in as tome it seemed like that was the last of the three parts that everybody says causes the issues. But over the last few days something didn't quiet add up to me which is why I'm here now.

I took the car out for a test drive and it does drive fine on the paddles even when coming to a stop at a junction, now in my mind and from googling around for info on the gearbox/Mechatronic unit, the dual clutch is a shared component whether you're in auto or manual gear selection. So if it works fine on the paddles how could that be the faulty component? The fault code thrown up again at the garage was for gear selector 2, which from looking at diagrams when I sent the Mech off for testing is a hydraulic component on the Mech unit used for gear selection. I remember seeing them with the chunky hooks on to push/pull the gears. But again, wouldn't this also be a shared component between auto and manual selection? So if it worked on demand through the paddles, why would it fail in auto? So by that trail of thought it has to be something controlling the auto side of life and not the manual which would be the Mechatronic unit or one of the sensors feeding into it that is only required for auto.

If anyone with more experience could throw some more light on this it would be greatly appreciated. I get that these aren't simple gear boxes so there is more than likely something I am not aware of but if the dual clutch is just a mechanical component then in my mind if it works for one then it's working for the other and the fault lies elsewhere. I'm only out to get extra opinions as £1200 is a lot to throw at another component after the previous fixes just to see if it fixes it. So the more info I'm armed with, the better.

Thanks in advance,
Stu.