Karobg

Hi guys,

I would love if someone give me hints on this...

Here's my issue. I have an Audi A6 C7 2013 3.0 TDI Quattro (245hp) with a 7 speed S-tronic (255,000km).

Two weeks ago after I stopped at a red light I have noticed that when I let go the brake pedal the car rolled backwards (I was on a slight uphill - acts just like in neutral) instead of going forward. I pressed the gas pedal and then the car go forward but little roughly. Then when I've arrived home I put in reverse to park and the same thing - just like I'm in neutral, but this time a warning light come to the dashboard "Gearbox fault - you can continue driving" followed by "Gearbox fault - no reverse". But the car goes forward and reverse (roughly) when I press the gas pedal... On the next morning I've started the car and there were no warning lights on the dashboard - I drove the car for a few hours that day without any issues or signs of what happened last night.

I've took my VAG-COM and the following error codes were stored (2 Fault Codes):

8955 - Valve 3 in Transmission Part 1
P17D4 00 [104] - Mechanical Malfunction
8960 - Valve 3 in Transmission Part 2
P17D5 00 [096] - Mechanical Malfunction

I've drove the car with no issues for a week when suddenly the same thing happened - the gearbox acted like it's in neutral with the same warning light, but this time I was able to drive the car only using 2, 4, 6 gears. I have stopped after a mile or two. Started the car again - no warning lights and I was able to drive the car as I normally do. All gears works and shifts fine. The strangest thing is that now the old 2 fault codes are gone and a new fault code appeared this time (1 Fault Code):

18011 - Gear Selector 2
P187B 00 - Engagement not successful
Intermittent - Not Confirmed - Tested Since Memory Clear

Now a week after this happened the car is working and acting as expected with no fault codes or strange behaviors... Do you have any hints for me guys? Isn't this strange?

Just want to mention that this happened a few days after oil change (transmission) - not sure if there is a connection.
(Also when happens the engine and transmission are warm.)

Will appreciate any opinions on this.

Thank you!

superswiss

Most likely you have a sensor that's on the fritz or a solenoid going bad. Unfortunately, the S-tronic has a lot of moving parts and sensors to keep track of everything and when they start failing it gets expensive, because most of the sensors are inside the transmission, so it needs to be taken out and disassembled. I had the gear position sensor fail in the S-tronic of my '13 RS5. The sensor is like $100, but the whole job is $6000. Audi agreed to a 50/50 goodwill, so I didn't have to pay for the whole thing, but it was the final straw to sell it.

However, rolling backwards on a hill is technically normal for the S-tronic, because like with a manual transmission, when you come to a stop the clutch opens and the wheels are completely disconnected from the engine, so the car rolls backwards if you don't hold it with the brakes. To avoid this it's equipped with Hill Start Assist, which is supposed to hold the brakes for you for a couple of seconds to give you time to switch over to the throttle and start moving, but if you wait too long the brakes release and the car starts rolling. If the Hill Start Assist isn't engaging, then that's another indication that some sensor is working incorrectly and not telling it that you have come to a stop or it thinks the transmission is still spinning or something.

Karobg

Thank you for the reply. That's possible, yes, but before that moment my car was never going backwards when I let go the brake, no matter if I'm on uphill or not. There was always a little delay, but never rolling back.

One thing that I was told - is it possible to be a low oil level in the transmission?

Also I think worth mentioning from what I learned - the transmission would never make an issue if not 100% warm.

PEB60

After the fluid change did you clear the adaptations with your VAG Com? Then, did you relearn the transmission according to the recommended drive cycles?

Karobg

Thank you for the reply. I asked the guy who changed the oil - no, just fluid and filter changed. He said that he think it isn't neccessary when just changing the fluid. Can this cause problems? How to do that relearn process and clear adaptations?

superswiss

Yes, so Hill Start Assist was working correctly before, but now it's not working anymore for some reason.

PEB60

I am in the US and actually have the ZF8 Tiptronic so I am not sure on how to advise you other than to say my transmission changes the way it operates to allow for the supposed "lifetime" fluid to degrade.

Once you refresh the fluid, the car needs to be told so shifting patterns and clutch activity can be reset.

As far as how to readadapt/retrain the s-tronic, do yourself a favor and do a little research. You can learn a lot about your car if you use Google correctly and filter what you see. I find the forums aren't very forgiving to those unwilling to do a little discovery themselves!