KYNZ

Paul, you should make the TECH writeup for this on Audipages a PASSWORD PROTECTED file! hahahaa

PaulW

However, I really don't want to be spending $100 here, another $89 for the output sensor, etc.

I would rather figure out what the problem is and this will require one step at a time.

Your idea is a good one, but my budget is another, I have spent about 1/3 of my car's value on the transmission lately and just don't want to flush any more $$ down the toliet, and more importantly, I want to determine what the real problem is by doing it one step at a time.

My problem is very different from your problem, no fault codes, no limp mode, it's the torque converter dropping out.

Thanks!!

MP4.2+6.0

Every time you open the tranny pan it's about $100 for fluid and filter/gasket set and a couple of hours unless you are re using something or using one of the non-Audi/Pentosin fluids at a lower price.

But I admire your tenacity. Mine was different, but it's still in exactly this same intertangled sensor area--the materials you posted really brought home the point--where problems are likely to arise. Part of the valve body also powers the torque converter lock up (and presumably slip) as I recall. I don't know where it gets the load signal from, which I expect would feed heavily into the torque converter general functioning. Logically it's either from the ECU where it's looking at the throttle position, MAF readings, RPM, etc., and/or its some kind of triangulation with the tranny sensors and the rest of what TCU has already computed and told the valve body as far as gear selection.

Have you found anything that says where the load signal comes from? The materials I have from the Audi training type publications basically just do a handwave at an interrelationship among lots of sensors, the throttle, the computers and the MAF. Seems to me in thus question are likely answers about where to keep looking. The first paragraph of the materials you attached refer to the load on the engine, but still don't crack the code on where the signal is coming from. You might guess they are saying the engine ECU, but it's somewhat unclear. I also know whom VAG COM I can read moment to moment what's going on with torque converter slip vs. engine RPM. Pretty amazing--I never guessed it used this much slip until I say the data every quarter up and down the shifts in town and out on the freeway. Basically it never locked up until I hit the freeway in typical suburban driving without long periods at constant speed, and the slip was minor to 400 rpm. I also know from Lemmiwinks that at the TCU I can force more idle torque onto the tranny (if I believe the settings do what is published), which suggests to me the TCU not only knows what's happening here, but can also alter it. No answers here, but maybe you can make something of this.

PaulW

Tozo had problems with his tranny, and had hunting and thumping. He has a 97, his name is Gabor if you don't know that already.

In the end, it was the clutch fingers that were ripped I think or something, but that really doesn't matter.

He bought a tranny from an 02 that was wrecked.

Instead of changing out the tranny, he first tried the valve body, which included the speed sensor, but not the wiring harness. It did not solve his problem, which would require a rebuild.

He put the 02 tranny in, worked perfectly. No hunting, no thumping. So it had the speed sensors that came with the tranny (relatively new), internal and external for output speed.

It then ripped one of the clutch finger plates and it lost second gear. In an effort to troubleshoot it, he swapped valve bodies out of the 97, keeping the speed sensor on each respective valve body, but the wiring harness stayed in place.

It would start to thump and hunt, and it did not solve the lack of 2nd gear problem, which required a rebuild.

So we thought it was the valve body for sure, but a rebuilt unit had absolutely no change on my car. But we had to swap speed sensors from my old one to the rebuilt one because it didn't come with one.

Since his car went from no hunting to hunting with a change of valve bodies and input speed sensors (output speed sensor stayed in place for both tests), there is a chance it's the speed sensor. He had no change in wiring harness.

Odd that this only happens on the A8 and not the A6, but the A8 has SUPER tall gearing that did not come on the A6. Something like 47 MPH in first gear alone. It drives around at 1200 to 1400 RPM all the time.

And as I was driving my kids home, I was thinking about your posts, I'm probably being more stubborn than anything.

I've been working on this problem probably longer than any other thing in my life, about 4 years now. And I still feel like I'm at block one.

But I sure know how this damn car is put together!

BTW, we're using Valvoline fluid, and I'm just draining it to a clean bucket and reusing it. It has about 300 miles on it.

MP4.2+6.0

Take these combinations of things and put them into a table sort of format (if you know Tozo's data), with headings like tranny housing, valve body, input sensor, output sensor, harness, torque converter, etc and then fill in the rows with 97 and 02 and the final column being did it work or flop. There are a bunch of permutations in here and I am not sure I follow all the variables, like did the torque converter get swapped over or not in the ones where the tranny was pulled. Maybe I'll see something there, or I can e mail coordinates off line.

We're a lot closer than you might think as far as mechanicals. The A6 4.2 also has the super high gearing--2.727 final drive, which I think is yours too. I think all the gears are the same too; it is in first anyway. It's the S6's that are geared a bit lower, as I think the S8's may be likewise. I leave 1st at a little over 40, leave 2d at about 75, and IIRC (theoretically speaking) leave 3rd at about 105. Thus I cruise around suburbia at 1200 or 1400 rpm a lot. My 4000 pound weight is also pretty similar--smaller body but steel, with the newer aluminum suspension bits and the aluminum front clip. I think the only material drive system differences are in the wheel running diameters--oversimplifying C5 A6's are basically one major size down. Tire for tire width wise probably an inch down on rim size or an aspect ratio step down at the same rim size. That gives you probably the slight difference in MPH shift points. Audi bobs and weaves on where the 10 HP difference is, usually referring to more space for the intake or the header as opposed to detuned for marketing reasons. I used to think it was really in the ECU programming, but now think it's basically the throttle plate trick. My throttle body is noticablly smaller than the intake it bolts to and I see from Audi parts listings the A8 uses a different part #; if yours is the same size as the intake passage it bolts to, I'll have my answer.

The A8 crowd has higher mileage cars than the A6's with several years earlier production, but you can now see the tranny problems revealing themselves. The torque converter drop out doesn't sound common in the A6 postings I see. Mostly it's lost reverse, chewed up internals, some blown converters and the clunk. And the clunk goes over to the smaller 5HP19 and I know from personal experiece affected the old 4HP18 (?) used in the older C4 100/A6.

PaulW

Danke

audibadboggy

I'm about to change the output speed sensor too, I bought the car two years ago and I've been having problems with the tranny, the 4th and 5th gear issue ...until a few days ago when the transmission went into a limp mode and and check engine light came on and I got the gear ratio obd error code 17114. I've done two filter/oil changes that I though will fix the 4th/5th gear problem and it didn't. My car is a A8 97 with a DSM type trans. Went to the dealer and asked them for the output sensor and they gave me the wrong sensor I think, the speed sensor part # 01F409191 vechicle speed sensor, so i will have to take the old one out and take it to the dealer to get a replacement. Does anybody has the correct part number for that output sensor?
I will give an update to see if it fixed the problem once I change that sensor.

A7Guy

I know this is an old thread but I have a issue with code p0726 where’s its saying transmission input speed (rpm) sensor 3 (rg.35) .. how do I fix this? Can I just buy the speed sensor 3?