Help! C5 Allroad Tiptronic Transmission(s) No Engagment

[Ringo970]

I am hoping for some ideas and guidance from the expert community here. I bought a 2005 Allroad with a “bad” Tiptronic 5-speed transmission last month. My thought, and hope was to swap it out with another known working AT I pulled out of an AR when I performed the infamous 6mt swap (which went great BTW, still going strong at stage 4)

The codes that the TCU had stored:
P0730 - Gear Ratio Monitoring
P0811 - Excessive Clutch Slippage

So, I made the switch, did a timing job and some other tune-up items, filled the tranny-to manufacturer’s specs of course. Everything went great and the car engaged in gear and I reversed down the driveway and went for a test drive around the neighborhood at speeds of no more than 25mph. About 1/4 mile from home the vehicle went limp and I had no power from the tranny, again. There was no reverse, no drive, the motor just revs regardless of what gear is selected. I plugged in the VAG-COM and it shows the same codes as it did with the previous “bad” tranny, P0730, P0811, and a new one possibly a result of me moving the gear selector into tip mode P1756 (Tiptronic Switch fault). Also, The bottom of the LCD display screen reads in all red PRNDS, which I assume means the tranny is in some form of limp mode

I am really hoping that this is an electrical/computer malfunction. I find it very hard to believe that a know good AT would be fried in less than a mile and display the SAME fault codes

Could this possibly be the TCU all along? Is there a procedure that I have missed that I need to perform to clear/reset the TCU?

I went into the Transmission adaptation and input “000” to perform a reset on the TCU but that did nothing, unless I didn’t do it correctly for somehow.

I have another TCU, the one that went with the AT that is now in that vehicle actually. I have read that they are specific to the ECU though and the last digit has to match if you choose to replace.

Any help or ideas is greatly appreciated!! I have also posted this in the Drivetrain Tech Forum in hopes that someone might have some thoughts.

[4xaudi]

Did you chech under the passenger side carpet for a swimming TCU? Water gets down there and destroys the electrical contacts.

[rollerton]

So it did drive under power briefly huh? Can you clear the codes and get it to drive the short trip again _or is it just spinning and no go?
If you clear the codes and start it does it go into limp almost immediately or is there a trigger? Can you sit in one place and shift through the gears without driving or does that cause limp mode?
You can check MBV in VagCom and shift and see if a specific gear triggers the fault- that F125 switch/ shift cable is somewhat adjustable.
If it does drive briefly You could also try putting it into a different limp mode-maybe start it up and pull the MAF connector, that usually causes a limp mode. See if 'engine' limp mode is different than trans. You can definitely swap the TCU, worst case is it's not compatible.

The fact that the trans WAS good and it drove for a minute or two is a good sign..but still a hassle.

[Ringo970]

So it did drive under power briefly huh? Can you clear the codes and get it to drive the short trip again _or is it just spinning and no go?
If you clear the codes and start it does it go into limp almost immediately or is there a trigger? Can you sit in one place and shift through the gears without driving or does that cause limp mode?
You can check MBV in VagCom and shift and see if a specific gear triggers the fault- that F125 switch/ shift cable is somewhat adjustable.
If it does drive briefly You could also try putting it into a different limp mode-maybe start it up and pull the MAF connector, that usually causes a limp mode. See if 'engine' limp mode is different than trans. You can definitely swap the TCU, worst case is it's not compatible.

The fact that the trans WAS good and it drove for a minute or two is a good sign..but still a hassle.

It did drive, yes, and I was about to celebrate another resurrected Audi...and then it completely failed. I had my laptop, plugged in, and got the same faults as I did from the old AT. I tried clearing the codes both in the engine module and the transmission mod, nothing. Disconnected the battery overnight, no codes, and still nothing from the tranny. It just spins, it has completely disconnected the clutches from engaging in any gear.
Since I posted I have tried a different TCM, the one that came in the vehicle is a "T" and the one I tried is an "M"...no go.
That's interesting thought about monitoring the tranny via VCDS to see if it registers a request for gear change through the tip, I'll give that a go and report back.

The other thought is that what are the chances someone tried changing the rear diff and actually put on one from an A6?? The computer both times spit out a "gear ratio monitoring" fault. I have no idea what the history on this car is and I feel as though the seller was not completely honest but in any case, I have a rear diff for the AR and I figure I might as well try it.

Cheers,
Ed


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[Ringo970]

Did you chech under the passenger side carpet for a swimming TCU? Water gets down there and destroys the electrical contacts.

Thanks for your reply, it's one of the first things I checked and it was fine. I was REALLY hoping I would find corrosion our water but not the case. I actually tried a different TCU but no luck. Although, it was an M trying to replace a T box so I'm not sure if there was a compatibility issue but regardless, no go.

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[rollerton]

The other thought is that what are the chances someone tried changing the rear diff and actually put on one from an A6?? The computer both times spit out a "gear ratio monitoring" fault. I have no idea what the history on this car is and I feel as though the seller was not completely honest but in any case, I have a rear diff for the AR and I figure I might as well try it.

Cheers,
Ed


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You could check the code on the rear diff- but as far as I know there's no monitoring of any kind of the rear diff. I've heard of people actually driving around with mis-matched ratios and while we all know it's wack! - apparently it's not super noticeable for the most part and you can drive for quite a while before causing any super noticeable damage.
Other than some investigating visually around the axles and and using VCDS to see what the trans is trying to do that's a tough one. You might even try disconnecting the F125/ trans switch and see if it acts any different. The auto trans IS mechanical for the most part; if the pumps/valves and guts and TC are more or less working you'd think you'd get SOME kind of output from it?

No ABS faults? Not sure how it could matter- just for speed sensors or something?...but you never know.

[mc_hotmail]

I have a C5 allroad and a B7 A4 quattro. Once the B7 console all PRNDS lit up, because it lost a magnet in the shifter. It's worth investigating even though it's not the same car:

https://www.audizine.com/forum/showt...1#post14176809

[Ringo970]

You could check the code on the rear diff- but as far as I know there's no monitoring of any kind of the rear diff. I've heard of people actually driving around with mis-matched ratios and while we all know it's wack! - apparently it's not super noticeable for the most part and you can drive for quite a while before causing any super noticeable damage.
Other than some investigating visually around the axles and and using VCDS to see what the trans is trying to do that's a tough one. You might even try disconnecting the F125/ trans switch and see if it acts any different. The auto trans IS mechanical for the most part; if the pumps/valves and guts and TC are more or less working you'd think you'd get SOME kind of output from it?

No ABS faults? Not sure how it could matter- just for speed sensors or something?...but you never know.

I agree, I am stumped that I am unable to get it out of being completely disabled.

The fact that I get the same faults out of two different transmissions leads me to believe that it is nothing actually attached to the transmission nor is it anything within the box itself. I could be completely wrong but what are the odds!

I am planning on doing more diagnostics this weekend including disconnecting the F125 switch to see if anything changes. I'll inspect the wiring harnesses and track wiring to see if I see any damage.

I have an extra ECU (from a 6mt) and I'm tempted to soft code that for the AT and see what happens.

Apparently there's a local guy that programs TCUs to match VINs and I'm considering contacting him to see what he thinks.

I'll post updates to let you know what happens.

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[Ringo970]

I have a C5 allroad and a B7 A4 quattro. Once the B7 console all PRNDS lit up, because it lost a magnet in the shifter. It's worth investigating even though it's not the same car:

https://www.audizine.com/forum/showt...1#post14176809

Thanks mc_hotmail, I will definitely be taking a look at that this weekend.

I am pretty well convinced that it has to be something like this, something in the car itself causing the issue. What are the odds that the same disabling codes happen with two different trannys??

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