steve1990

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.

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

2001 S8

I had the same issue a couple of years back at 115,104 miles. Your F drum in the transmision is broken. The transmission worked fine with forward gears but nothing in reverse. The only fix is a re-build.

Good luck

steve1990

Ahh that doesn't sound great...

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 is moving at a certain speed when it isn't therefore not allowing it to go into reverse or shift down to 1st too early. Does that make sense?

hillpc

That leaves open the possibility that it's not the F brake since the F brake is required to run reverse, even though it is the most common failure mode for reverse. The C clutch is also required, but for that you still have to dig into the guts of the trans. Maybe you're onto something.

clutch logic table

twentysevenlitres

I love it how everyone immediately jumps on the transmission rebuild band wagon!

The 2.8 A8's don't use the 5HP24A.
They use the 5HP19/A (yours being FWD won't be the A (AWD/Quattro) variant).
I would replace the G182 input speed sensor.

To get a better handle on this, jump on the A8parts forum and contact MikkiJayne. She knows her stuff and is reasonably local to you in Devon.

MikkiJayne

For closure, I bought the car from Steve and it definitely has a broken clutch drum (shiny chunks in the sump). It will reverse with the TCU removed, as the transmission just reverts to a single speed (3rd) hydraulic automatic with no electronics, and then it puts full line pressure to the clutches which is enough to engage them. With the TCU in place it's modulating the clutch for a smooth shift, but as the end of the drum has fallen off that's not enough pressure for the clutch to grip.

2001 S8

Thanks for the follow-up and putting any questions/doubts to rest.

Good luck.