Audi A8 D2 2.8 V6 Transmission issue - Wont engage Reverse - 17100 Fault code
 

Hi everyone,

I did the usual search before I posted but couldn't find anything conclusive, so here goes...

I have a 1999 Audi A8 2.8 V6 2WD 5 Speed Automatic.

The car was driving fine aside from some joltyness at low speeds, its almost like the throttle pedal is an on off switch, you couldn't apply the throttle smoothly/ gradually. I put this down to knackered engine mounts as you can feel the car move even when you rev at a stand still. Another thing that may have played a part in the failure is my handbrake, it is very poor and sometimes when parked on a hill it relies on PARK to hold the car so when you get back in and shift to drive there is a nasty clunk. (not ideal I know but I have had a busy few months so let it slide stupidly)

Anyway I parked up outside my house as normal and when I came out to drive to work the next day, went to reverse off the drive but it wouldn't engage reverse so would just rev like I was in neutral.

At this point the car wasn't showing limp mode, after some rather aggressive shifter movement back and forward (I was quite annoyed as I was running late as it was!) limp mode was engaged (red showed around all the gear display on the dash) it finally let me reverse a bit, then when I changed back into a forward gear it just stuttered and the engine stalled.

When I turned it back on again the limp mode was off and I couldn't reverse, I plugged in in with my scanner and aside from a load of central locking/alarm related codes the only transmission related code that came up was:

17100 Transmission Input Speed Sensor (G182): Implausible Signal P0716.

I've seen this code pop up a lot on forums after a thorough search, but none seem to have the issue of no reverse, could this code cause the transmission to not select reverse? or am I looking at an internal mechanical failure, I know these boxes blow the seals an loose pressure causing all sorts of problems.

If not, any other suggestions? I don't really want to spend a fortune on a car that I was planning to sell anyway, but at the same time if its a matter of changing a sensor and carrying out a transmission fluid/filter change it might still be worth doing.

*EDIT*
I was having a fiddle with it over the weekend as I was a bit bored and it reverses absolutely fine in limp mode, and I also noticed when I change from auto to manual mode sat still it shows it as being in 3rd gear then it won't let you go into 1st when you try and down shift, it will just stay in 2nd... then if you try and knock it down to 1st it thinks about it then just stalls the engine.

Does that sound right? it's almost like the transmission speed sensor is telling the ECU that the car is moving when it isn't therefore not allowing it to go into reverse or shift down to 1st too early. Does that make sense?

Any help or pointers will be greatly appreciated.

Its worth mentioning I work on cars and have a workshop with a ramp and all the tools ( we mainly carry out engine conversions on MK1, Mk2 Golfs but also build and prep track/race cars.) So I have the facilities to carry out any work on my own, I'm just not that familiar with any auto transmission stuff!

Cheers
Steve

Unfortunately that's an internal mechanical failure - one of the clutch drums has broken and so it can no longer properly engage the clutch pack. The implausible signal means that it has selected the gear and is reading input rpm but no output, because the clutch pack is slipping. The reason it works in limp mode is that the TCU isn't trying to be clever and shift smoothly by modulating the hydraulic pressure to the clutches, its simply putting full line pressure to the clutch pack which is then able to engage despite being broken.

This is probably what it looks like:

https://blog.bavauto.com/wp-content/...-325Z-0021.jpg

I have an Allroad with exactly the same problem. Shiny chunks in the sump, and won't move unless you un-plug the TCU.

Our sponsors have a few of these gearboxes in stock I think. Not too hard a job to swap it on an FWD model :)

Damn it.... I was clutching at straws with my theory on it! but then don't we all when stuff like this happens!

Thanks for the reply and the info though, thats really helpful... at least I can begin to work out what I'm going to do now.

It's a hard one, I don't know whether to break it up or buy a box and repair it just to sell it.

Anyone fancy a project!?! :ROFL:

Would it happen to have a black sport interior...?

https://media.tenor.com/images/d7d5f...a2d5/tenor.gif

It sure does, black heated electric leather

MJ right now...

https://media.giphy.com/media/olmyX3Ns0nk4M/giphy.gif

Yup :ROFL:

Let me know if it has a towbar MJ +++

Oh, in case I didn't make it clear in our previous conversation, yes please to the Isofix brackets!