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-   -   S8 with gearbox woes. Code advice please. (https://forum.a8parts.co.uk/showthread.php?t=13757)

Bushido 17th January 2018 10:19 PM

S8 with gearbox woes. Code advice please.
 
Yes, this is the s8 that people will be fed up reading about!
Used to belong to Ollie and is a gem - all aprt from its gearbox. Car has been off road a year now whilst trying to raise funds / abandon all hope and just call it a day.
As it was going up fro sale, I opted to get a fresh MOT to enable perspective buyers the security of knowing where everything else with the car lay. (must check if it passed! :ROFL:)
Quick recap. Car has 174k miles. Masses of history including gearbox oil. Driving out of a car park one day, put my foot on accelerator to pull away and the car just revved and sat stationary. Had NEVER had a sniff of an issue previously! Withy more revs, the car clonked in to gear, threw up all of the gear indicator lights on the dash and had locked in to top gear. It was limped home and used as little as possible thereafter until a replacement car was found.
Whilst away for MOT, my friendly mechanic managed to get it Vagcom read. It has thrown up these codes and information -

3 faults found -
17117 Gear ratio Monitoring
P0730 35-00 Incorrect gear ratio

18232 Pressure control valve 3 (N217)
P1824 35-10 Open or short to ground - intermittent

18227 - Pressure control valve 2 (N216)
P1819 35 - 10 Open to or short to ground - Intermittent

Of note, a specialist (and experienced s8) gearbox man condemned the box as showing all the typical signs of a clutch(?) at the very front of the box as being at fault. He was 100% sure that the almighty clonk when first taking up drive was all the evidence we needed. In fairness, the fella gave me over an hour of his time and was happy to show me on other disassembled boxes the problem he felt we had here.

Now we have the codes, does this shed any more light on the situation? All I would add is that the car has covered a couple of hundred miles whilst in this 'limp mode'. Whether this explains the incorrect gear ratio monitoring Im unsure?

All thoughts and experiences will be very much appreciated whilst we make some longer term decisions about the fate of the car.
Thanks as always for taking the time to read++++++

HPsauce 17th January 2018 10:29 PM

Did you clear those codes and scan again and once more after driving?

MikkiJayne 17th January 2018 10:39 PM

Interesting. The first code is almost always a blown clutch pack as your specialist said, hence no drive and limp mode. However, the second two are very unusual and indicate an electrical issue causing the slip. They would certainly trip limp mode, and the bang in to gear while in limp mode is pretty normal - in limp the TCU basically just gives up and the gearbox works purely on fluid pressure with very little finesse.

The first things I would do are:

Examine and clean up the big round connector on the bottom front left corner of the gearbox - make sure there is no schmoo or corrosion in there, and its all nice and clean.

Then, open up the electrics box in the passenger side rain tray and have the same good look at the TCU connector.

If both of those are clean then its time to pull the sump and test / replace either the internal harness or solenoids. I have both spare from blown up gearboxes.

I reckon there's a good chance its saveable +++

Bushido 18th January 2018 12:22 AM

Gotta love this place! ++++++

The understanding I was given by the box specialist was that the "thump" was the terminal diagnosis. You seem to be respectfully suggesting that isnt just a given?? Interesting...

If those spares may prove of value please drop me a line with some details and a price you would be happy with and we will see if the collective manage to save a great car from a pending doom.

Thanks again +++

HPsauce 18th January 2018 10:10 AM

Quote:

Originally Posted by Bushido (Post 136798)
the car clonked in to gear, threw up all of the gear indicator lights on the dash and had locked in to top gear.

I think in limp mode it "normally" goes into third gear, and fairly brutally at that.
Though if you were driving gingerly you may not have realised that?

MJ's expertise is on another level to mine but with my "problem-solving" hat on it "smells" to me much more like an electrical/wiring issue, the daemon F125 switch or maybe something in the valve body unit, rather than power-transmitting gearbox components.

What area are you in by the way?

MikkiJayne 18th January 2018 11:01 AM

Quote:

Originally Posted by Bushido (Post 136808)
The understanding I was given by the box specialist was that the "thump" was the terminal diagnosis. You seem to be respectfully suggesting that isnt just a given?? Interesting...

As Andrew said ^ limp mode and thump is often caused solely by the F125 switch with nothing mechanical amiss at all.

Slip is almost always caused by an exploded or burned out clutch pack, but those two solenoid codes make me think otherwise. After you've checked the external connections, pulling the sump will tell you for certain. If there are shiny chunks in the sump then it's a clutch pack and time for a full rebuild. If its all nice and clean then let me know and I'll pull the solenoids and harness out of one of my spares.

Shame you're so far away really. I would have liked to have a crack at this one :)

PS, drive it as little as possible like this. If it is an electrical problem, banging in to 3rd gear is the best way to make it a mechanical problem!

HPsauce 18th January 2018 06:21 PM

Quote:

Originally Posted by MikkiJayne (Post 136834)
Slip is almost always caused by an exploded or burned out clutch pack, but those two solenoid codes make me think otherwise.

Unless it was a sudden catastrophic failure of a clutch pack (possible of course) then there would presumably be some "warning signs" beforehand?
Just suddenly out of the blue staying in or going into neutral when Drive (or a specific gear) is selected suggests something else.

To my mind the "thump" (experienced it a few times) is the gearbox deciding/told to select a gear in an unmanaged way with a high-revving engine.
I've had a fair few of those (some with limp mode, some without) when the only issue was in fact a dodgy F125.

Bushido 18th January 2018 09:32 PM

Just recalling the initial failing...
Id been in to a car partk for an interview. Had obviously detailed the car over the nights before to look as s****y as me! :ROFL: No issues at all on 2 minute drive over. Left, reversed out and selected drive to exit. As i added a few revs and awaited the drive to take up, there was nothing up to 2000rpm. It just sat stationary. I think I switched the car on and off at this point and may have even locked / unlocked it to see if there was some quirky glitch. Tried to move away again and had no drive. Out of desperation, I gently squeezed the revs up and just over 2000rpm there was a horrendous thump and the selector lights on the dash illuminated. On adding revs to move, the car very lazily growled (Im catless!) and hauled itself in to life. It was obvious that it was in a locked higher gear but it was moving. I very gingerly moved on to a main road and as the speed increased the car became more responsive in its progress. From here on, each standing start was laboured but no thumps in the drivetrain.
Over the coming days, a pattern developed. It will take up drive in reverse without issue. The first attempt at forwards drive was always met with the thump - but you learnt to soften it. Very slow and sensitive raising of the revs to around 1800 (i think) and tickle it and it would more gently drop in to drive.
Then it was parked up and the investigation put on hold after the gearbox man condemned it with a potential £2500 rebuild price (which I appreciate isnt extortionate for this type of work)
Today, I have had a photo sent of the gearbox ecu (Im presuming on the bulkhead) and the pins are sparkling clean. I have passed on the rest of your great advice and see how it all develops.
Thanks again folks, Paul+++

Bushido 18th January 2018 09:33 PM

I only typed s w a n k y - honest!! :Confused:

Bushido 18th January 2018 09:37 PM

The car is based in ts12 +++


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