1audicrete

Hi there AW members, I want to make this quick and to the point. I am a new member to AW but not to VAG automobiles. I just recently purchased my sixth C5, I have a hobby of picking up neglected VAG cars for cheap and bring them back to life. What we are working on now is a 2000 C5 4.2 160k. The person I bought it from was asking 1800.00 us, It's body is a 8/10, interior 9/10, his listing stated it had transmission issues. Long story short I loaded up truck trailer and VAG-COM, went out to see it. Everything seemed to be in working order, car is complete, even still had the belly pan, owners manual, med kit, and even the original window sticker from when it was new. I test drove it about 3 miles, and after that 3 miles the car was up to full operating temperature, and this is when the problem starts, like clockwork, upon coming to a stop it down shifts some what hard, after coming to a complete stop and attempting to accelerate moderately it slowly moves forward then "pops" out of gear, me being somewhat educated on transmission issues with Audi immediately let off the throttle to avoid the inevitable "bang" back into gear, but that doesn't matter, still bangs back into gear. My first thought is low or contaminated fluid or a possible electrical issue. When I returned with the car now in limp mode I connect VAG and get nothing, interface not recognized. I know for a fact it is not my gear, I own 4 VAG vehicles and always check my cars before going to look at another possible addition to the family to make sure everything is working as it should. Anyways, I have seen this error before, it usually means there is a module interrupting the CAN communications somewhere in the vehicle, which then means, for me anyways, doing a process of elimination of module removal until VAG connects. So the owner was absolutely clueless about what i was talking about, I told them I needed to runs some more tests, and a quick hand shake +$200.00 us dollars I strapped the beast on my trailer and headed home with title in hand. Honesty is my #1 motto, Integrity is #2, I felt a little bad, but $200 was what they told me was their bottom dollar was and I took it. Part of doing business i guess. So anyhow, I got it home, stripped the car all the way down so I could access all modules and this is what I found, ABS module is not working, when connected wont let VAG connect, and also the motion detection module, located on driver side behind the rear seat bolster where the airbag is located, no matter what combination of connections made it disrupts communication. All other modules read as they should and here is the short brief version of codes pulled, *Note: by stripping the vehicle down I mean all the way down, all electrical connections have been inspected, I also did the transmission fluid and filter change with VAG now that it reads it.

Chassis Type: 4B - Audi A6 C5
Scan: 01,02,03,08,15,16,17,35,36,37,45,55,56,76

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Address 01: Engine
Controller: 4D0 907 558 S
Component: 4.2L V8/5V G 0006
Coding: 06652
Shop #: WSC 02325
1 Fault Found:
16885 - Vehicle Speed Sensor: Implausible Signal
P0501 - 35-00 - -
Readiness: 0000 1001

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Address 02: Auto Trans
Controller: 4B0 927 156 BS
Component: AG5 01L 4.2l5V USA 1414
Coding: 00032
Shop #: WSC 02325
1 Fault Found:
17116 - Gear 2 Incorrect Ratio
P0732 - 35-00 - -

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Address 08: Auto HVAC
Controller: 4B0 820 043 AM
Component: A6-Klimavollautomat 0105
Coding: 00010
Shop #: WSC 02325
5 Faults Found:
00604 - Potentiometer Positioning Motor for Air Flow Flap (G113)
30-00 - Open or Short to B+
00819 - High Pressure Sensor (G65)
30-00 - Open or Short to B+
01592 - Air Quality Sensor (G238)
57-00 - Electric Circuit Failure
01317 - Control Module in Instrument Cluster (J285)
49-00 - No Communications
01314 - Engine Control Module
49-00 - No Communications

Now with my story coming to a brief end, I have one question, The transmission operates well before reaching operating temp, even when driving it aggressively, but as soon as it gets up to temp, its done, goes into limp mode, I am okay with replacing the entire thing or I have a 6sp I may consider putting in it. I want to know if any one out there has experienced this issue and has repaired it? I am fine pulling it, I am equipped to do so, but its not exactly a quick a minute project. But if I had a better idea of what could be causing the issue would definitely help me move in the right direction, I have search high and low, made for phone calls to other VAG enthusiasts, with out much luck. Couple more small detrails, TIP works exactly like drive does, fine at cooler temp, not fine at operating temp, the warmer it gets the worse the slipping out the back in becomes. Reverse always works flawlessly in all conditions, the transmission does shift hard into reverse and into drive always, I am leaning towards a faulty pump, possibly a TC, I have checked out measuring blocks, everything from what I can tell is operating as it should. I am no expert with VAG-COM so I dont know exactly what each individual block should look like, but I do have a 03 C5 4.2 to compare specs to, even though the trans codes are different, VAG reads very similar number on both vehicles under all conditions. LMK what you guys think, I like to learn, I have spent 3 weeks tinkering with it now its time to either put new trans in it, or cut it up for parts, I paid $200 for it so I am not disappointed in any manner having a healthy 4.2 to add to a B5 project we have going. Thank you everyone, Knowledge is power.

Harleyguy

Almost sounds like the pressure regulator in the valve body has blown out. There is a vendor on here (maybe you already checked with her) OCLES.com is a 4.2L Tiptronic fanatic. She has a really knowledgeable tech that is well versed in these issues. She will probably see my reply and jump right in, in short order. Anyway that's my assessment assuming that you checked the transmission control module for moisture damage.

1audicrete

Thank you for the response, I will look into the information you provided. Thanks Again.

ocles_inc

Thank you, @Harleyguy

The way I understand the typical cause of this sort of thing is the clutch "A" drum snap ring retaining ridge, at the top of the basket, being pushed away from the basket due to abnormal pressure due to the pressure regulator in the front lower valve body housing having worn out enough to allow a pressure spike through. That disables forward gears 1, 2, 3, and 4 whether in TipTronic or otherwise, since they all depend on the "A" clutch to transmit the power to the appropriate gear(s) in the planetary gear set.

In severe cases, the "A" clutch is so messed up that it slips as soon as engine power is applied while the transmission is, essentially, in 1st gear. The car then goes into "limp mode" and the only forward gear is 5th. Reverse gear is not affected.

I haven't experienced the "fails only when warm" situation but, reasoning this through, I can imagine a disintegrating "A" clutch being held together just barely enough to exert enough pressure so that the plates grip well enough with thick fluid (as in, cold) but not when the fluid viscosity thins out (as in, warm).

Going by heuristics, this is the most typical failure pattern for these transmissions if the pressure regulator fails, so ... if I had to bet money, that's my bet.

But, it's just an opinion :-)

~Tanya

PS: I'd be interested in buying and fixing up your bad transmission, ideally with the entire car around it, after you've helped yourself to the engine, as long as it still looks like a car. Where are you located?

1audicrete

Thank you for your insight on my C5. I'm going to take a couple days to think about what I want to do with it, i was 90% it was a mechanical malfunction but wanted to share with the AW community to see what others thought. Right now the vehicle is 90% back together, has a couple pieces of trim that need to go back in, headliner is sagging so I'm going to fix that while I have trim out. @Tanya if you are very interested you can PM me and I can give you more info. I live in Michigan. Thank you for your time.

1audicrete

Hi Tanya, So I decided to take a dive into the ECF and as shown in my photos, the O-ring for the A-Drum input shaft had been damaged and literally fell out once disassembled. I am comfortable disassembling the gear box this far, but the valve body on the other hand is a touch out of my comfort zone, at least until I have the replacement parts, and with that being said, my research has lead me to believe this is a fairly common problem as you had mentioned, and ZF and other suppliers offer a "newer" version of the pressure regulator valve assembly. I plan to purchase that with the new o ring and new steel plates for the clutches. One other question, is there a way to tell if my torque converter has suffered any damage from the hard slams in and out of gear? I appreciate all of your insight and was wondering if the section i circled in the photo of the valve body is where the pressure regulator is located? Also if you have any further insight for me while i have the gearbox out and partially disassembled?

tanya_charbury

Hello again,

I haven't as yet come up with the funding or enthusiasm to renew my company vendor account on here for the next six months so for now I'm just responding as a trying-to-be-helpful individual. My vendor account is in disgrace until I renew it.

Basically, Nat Wentworth at the ZF distributor in Connecticut is a great resource for what to focus on. It's basically prohibitively expensive to replace everything in the transmission case with new parts, and he's got some street-smarts wisdom as to which items are most prudent to replace, though of course it's all intelligent guesswork and your transmission might end up needing something that just coincidentally doesn't happen to be on the magic list. So don't hold him accountable for not being clairvoyant. ...

An example is the little bearing that goes just outboard of the "C" clutch. That's a common point of failure so Nat recommended I replace it and so I did.

Assembling these transmissions is tricky; Gary Ferraro has some helpful videos on Youtube that I recommend. I'm supposed to be smarter than the average bear and it took me 2 years to be able to do it part-way with some level of confidence. On the plus side, so far the work done has stood up to the test of time, so no major failures yet (except for ... well, read on).

As to testing the torque converter ... after 100K of use my policy is nowadays to spend the $300 and get a renewed one from Nat. There is also a static test whereby you purchase a VAG tool and basically try to the fight the lock--up clutch and you use a torque wrench to measure when it gives way. It's about $54 for the tool but so far I haven't bought it; I just replace 'em (after a car recently ate its own torque converter soon after my tech and I had assembled everything, and that was gonna be our Virginia City Hill Climb race car last summer so it was a mad rush to get another car ready in 2 days. So, I get to say "never again." You might say "I'd rather save the $300 if I can " ... it's up to you whether to replace with a rebuilt unit or not. I go with "yes".

I actually don't know exactly where the pressure regulator is. I just mail the entire complete lower front (emphasis: front) housing off to Nat, he renews the pressure regulator wherever it is and from them on I have a valve body that refused to let me destroy the clutch A drum even though I drive my thus-renewed A6 4.2 V8 very vigorously.

I hope this was helpful!

~Tanya