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a8 transmission issue

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Old 07-07-2017, 08:44 AM
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Default a8 transmission issue

So im sure this has been posted 100+ times and ive read alot of threads related to it. But i want to see if there is any ideas to my specific issue.

So first time poster and unfortunately its not a positive first post.

the Car is a 99 a8 4.2 throwing trans code 17114 gear incorrect ratio. So i hooked up the vagcom and thought i confirmed the trans itself was OK. Its going into limp home mode as soon as its shifted into D, if you shift into D and mash the gas it wont throw the code. same thing if your coming to a stop and shift into N before hitting 0mph so the car is drive-able and seems OK... i replaced the trans fluid and filter- no change. replaced the tcm- no change so i think my last hope is to replace the f125 switch...ive cleaned the connection on the switch twice now with no success.. i just ordered one off ebay but im only about 20% sure this is going to fix it as its not throwing a code related to the f125.. Has anyone been in my boat before or am i sailing solo here? bought the car for $2500 and it has 148xxx miles. it was fine for 2 days after purchase and now this... please advise me audiworld
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Old 07-07-2017, 10:01 AM
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Sorry but you're looking at a trans rebuild. You most likely have a broken A drum.

Transmission Story

Either you got duped or just bad timing on the purchase.

Good luck.
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Old 07-07-2017, 10:26 AM
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Doing some research on the A drum now. if it was blown wouldnt the car be unable to move at all? video im watching says only reverse would work
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Old 07-07-2017, 10:28 AM
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Originally Posted by 2001 S8 View Post
Sorry but you're looking at a trans rebuild. You most likely have a broken A drum.

Transmission Story

Either you got duped or just bad timing on the purchase.

Good luck.
i also see your in south dakota. Im over in Rapid City.
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Old 07-07-2017, 11:46 AM
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Do all the lights (P,R, D, N, 2, 3 & 4) light up on the cluster? Limp mode is 5th gear, so you'll still be able to move the car. I would guess by "mashing the gas peddle" you're somehow bypassing limp mode.

Could be the Valve Body but based on age/mileage of transmission best bet is drum failure. What's maintenance history on the transmission?

Yep, I'm in Sioux Falls.

Good luck.

Last edited by 2001 S8; 07-08-2017 at 04:54 AM.
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Old 07-07-2017, 12:03 PM
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Originally Posted by 2001 S8 View Post
Do all the lights (P,R, D, 1, 2, 3, 4 & 5) light upon the cluster? Limp mode is 5th gear, so you'll still be able to move the car. I would guess by "mashing the gas peddle" you're somehow bypassing limp mode.

Could be the Valve Body but based on age/mileage of transmission best bet is drum failure. What's maintenance history on the transmission?

Yep, I'm in Sioux Falls.

Good luck.

unknown history on the transmission, i kinda knew i was taking a gamble with the car but didnt think it would bite me in the *** so soon. yes prnd432 light up on the dash and puts it into 5th gear giving me no power. if i shift into D and hit the gas quick enough i must be bypassing it, as soon as it hits zero mph though its back into limp mode. it still drives great when its not in limp. Crazy to think that its the trans and not electrical.
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Old 07-08-2017, 04:54 AM
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Default valve body crack?

I wouldn't think a broken A drum (very common; I'm about to fire up my 97 A8 after taking many months to finish rebuilding it) would allow anything other than 5th gear and reverse, regardless of throttle position.

When I took mine apart, in addition to the broken A drum, I found the often cracked valve body. See thread https://www.audiworld.com/forums/a8-...-ring-2902807/ for a picture and discussion. I had it welded up by Eriksson Industries in CN, and got the improved pressure regulator valve already installed inside a replacement (used) lower front valve body section, (the "valve body" is several pieces that bolt together) so it doesn't happen again. Tanya/OCLES (see that post and others) may have some for sale.

I wonder if you've cracked the valve body (from the regulator sticking) but not yet blown out the snap-ring ridge in the A drum. I don't know enough about the valve body operation to know if this would cause your issue. I can only speculate that pressure leaking out the crack would be less of an issue at full throttle because the pump can keep up. On the other hand, full throttle with a stuck regulator is what can blow the A drum because the pressure won't be relieved. Did you thrash the car after you got it?

I did the valve body repairs and replaced the F125 switch before pulling the trans, but alas, those did not help.

Somewhere I read of a guy driving the car for a long time with only limp mode available.
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Old 07-08-2017, 10:54 AM
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@hillpc Thank you for mentioning me. :-)

@EuroGuy85 If I'm understanding you correctly, you might be in a good situation. It might be electrical. The output speed sensor or wiring might be the problem.

A couple of months ago, my tech and I did a rebuild on that same type of transmission. Unbeknownst to us, the output speed sensor wiring was iffy. The transmission control module kicked the car into limp-home mode. We'd just installed a brand new clutch "A" drum and in the valve body, the pressure regulator was the renewed unit, so ... it seemed unlikely.

We found that that the transmission control module didn't opine as to the gear ratios being incorrect, below 10 mph. So, below that, the car behaved fine. We could mash the throttle and the car behaved well ... until 10 mph.

I plugged in a USB cable that I had bought from Ross-Tech and I measured the output speed for the transmission, while my tech drove. It showed zero mph. Aha! He replaced the wiring, and the car has been a rocket-ship ever since. So, I propose you focus on the advanced values and measure the output speed while the car is moving. If zero, there's your problem. Measuring the input shaft speed problem couldn't hurt, either.

As I understand things, if your clutch "A" drum had blown, the car would slip at any speed in any *forward*[clarification added belatedly, thanks to wise input from @hillpc] gear other than 5th, and you couldn't get to 5th unless the car made that the only selection.

One of our 4.2 V8 project cars with that same transmission has been driving for almost 2 years in limp-home mode. 5th is the only way forward. Slow starts, but you can get speeding tickets even in rural Nevada, once it picks up speed.

A far less likely cause might be that your TCM is toast. I have a spare unit for sale if you need one, specific to the 99 A8. If you need a spare valve body to swap out, I have that too, specific to the 99 A8. Please look at the rectangular green ID plate on the driver side by the side shaft, and let me know the three-letter code that shows the variant of transmission you have. Some mix, some don't.

Once you have the problem isolated, by sure to do the preemptive fix on the valve body pressure regulator so your clutch "A" drum stays happy for another decade or so.

We're in the Reno area so worst case, road trip. Yes, in 5th. It's freeway all the way, so ... hey. Or, plan B, if it's established you need a transmission, I could drive my own 99 A8 up to where you are, and then you can road test the transmission and then buy it from me, and I'll make it my issue to get the car back to Reno somehow. It would come with a 3-year warranty on the clutch "A" drum, and it'd have the renewed valve body pressure regulator. I'd need a little advance notice but I assume you're OK with that.

Even if the above advice ends up not helping you, I buy your point that it's prudent to eliminate electrical faults, first.

I might be missing some things, so if this is flawed logic, please (anyone, everyone) be candid.

~Tanya

Last edited by ocles_inc; 07-08-2017 at 01:02 PM.
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Old 07-08-2017, 12:33 PM
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Some good info in there, Tanya; thanks. A very slight clarification of

[QUOTE=ocles_inc;24998182As I understand things, if your clutch "A" drum had blown, the car would slip at any speed in any gear other than 5th. [/QUOTE]

Reverse will work fine with a blown A drum. You probably meant to say this.
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Old 07-08-2017, 01:00 PM
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Default Correction

Originally Posted by hillpc View Post
Some good info in there, Tanya; thanks. A very slight clarification ... Reverse will work fine with a blown A drum. You probably meant to say this.
I know this and yet I phrased things misleadingly, oops. Yes, I totally agree. Thank you for clarifying.

Reverse doesn't need the "A" clutch and it works just fine even with a blown clutch "A" drum.

:-)

~Tanya
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