Weave

Morning Audi members and gurus .... I have a 1998 Audi A8 I purchased w 140k mi on it, previous owner invested $8k dollars and gave up on the car. I am in San Diego, CA .... The car starts, drives but PRND are highlighted in red. Its in safe mode, I had the trans serviced yesterday w filter and ZF Lifeguard 5 fluid. Technician found large connector to TCM not connected in front of trans / engine while looking over the car. He reconnected the two, the block lights disappeared off the dash board (PRND). The trans fluid was topped off, car was lowered for a test drive. It shifted smooth into reverse as I watched the car back out. tech put the car in Drive and rev'd the gas, it wouldnt drive forward. He shifted into park, reverse, neutral and drive ...car will not drive or engage in forward gears after plugging in the connector? We pushed the car into the lift, raised the car up, disconnected the trans cable like it was ...car goes into gear, R and D but back to safe mode again. Why would the trans cable be disconnected? How can I get this car running smoothly again? Please advise ... what should i do, Is it a TCM re-program???

I welcome some direction and advice ...thanks Weave

hillpc

Strange. The clutch logic diagram


shows that the A clutch is required for all forward gears except for 5th, which is the gear that's running in limp mode. The A clutch is a notorious weak spot in these transmissions, but it breaks at least partly due to another issue with the fluid pressure regulator in the trans valve body. My A clutch was blown when I got the car, and would run fine in reverse, but it would rev up and then slam into limp mode in any forward range, lighting the PRND432. (Do you have 432 highlighted as well?) I have heard, on this forum, about people driving the vehicle for a long time in limp mode, but a lot of city driving in limp mode would probably not be good.

The strange thing to me is that your trans won't move forward with the electrical connector hooked up, [note on terminology, therre's a trans gear selector mechanical cable, so I called your bundle of wires "connector" to avoid confusion with the cable], but your trans also doesn't go into limp mode and light the PRND432. I wonder if the TCU got flooded and corroded some connectors, or fried. You should pull the lid off the ECU/TCU box under the hood and see if there are signs of past wetness. Disconnect and reconnect the connectors? Getting water in the box is common, and there are multiple posts here and on other sites about clearing some drains, which collect debris and don't allow water dainage.

Weave

Morning hillpc .... yes I do have “4,3,2” also in red on the dash board. I will check the TCM under the hood, right hand side again. When I checked and disconnected the TCM, it looked dry and in operable shape. I’ll examine closer when I check it out. It is interesting how the TCM plug is not connected but the car drives well, starts off slow from a red light but picks up speed and cruises smoothly. I do have 2 error codes, one is for trans solenoid and the other for solenoid connector. I’ll investigate them but how can I compare the vin and green plate on trans to see if someone put a used trans in but didn’t match them together? I have pics from Tues trans filter / fluid change. Old Fluid looks worn, some metal flakes on magnet and couple small metal around the trans pan.

i appreciate your input, I’m curious to understand how to put this car back to OE operation. It makes no sense the course of repairs to be at this result. 2 shops said I need to rebuild trans and reprogram for $4,200 but I think it’s overboard since we don’t know the cause and effect as it sits. It runs and drives w out TCM how?
Thanks Weave

hillpc

It runs and drives without TCU because that's what limp mode can do. Kills the power line going into the trans to get completely hydraulic operation, 5th gear only forward gear. What solenoid codes do you have? Any signs of the wire bundle being scraped or melted against something? If it's really just a solenoid or solenoid wire, that shouldn't require a rebuild. That stuff can be accessed from underneath without pulling the trans. The solenoids are on the valve body. I did a bunch of messing with the valve body, fixing some stuff that needed fixing anyway, before I finally had to pull the trans for a rebuild due to the blown A clutch. Here's some stuff on solenoids, but I don't know how to read the EDS-5 solenoid page.





I don't like the looks of all the metal filings stuck to the magnets, but have no clue if that's excessive or normal.

DTE is a legit code for a 1998 trans, but there seem to be others. The white options codes sticker in the trunk should tell you what came in the car. Mine's on the left side near the spare tire tools. It shows ABZ engine, DGZ rear axle, and DPZ trans in the first line. I can't speak to programming the TCU.

Weave

Morning hillpc, thank you for the information. The 2 codes that show for my A8 are P1747 - trans solenoid power relay open or short to ground. P0716.1 trans input speed sensor (G182) implausible signal. I did my best to research these codes to better understand but I’m relying on the local mechanics notes. I read your reply and think I may need assistance w the above mentioned. I would hate to be misdirected into a $4,500 rebuild. Any referrals for trusted mechanics in San Diego?

I will I’ll look at white sticker in trunk to confirm that this is the original trans or possibly a replacement. At this moment I’m at a stand still. I’m not sure which way to go or where to bring it next. The previous shop only services trans not diagnose or chase down my fault codes. They kinda gave up and showed no interest in getting more involved.

I appreciate your feedback
Weave

jfrahm

Hi, sorry to hear about this. A 1998 A8 in decent shape and running/driving with 140K miles on the clock is probably not worth $2500. It'd be hard to spend $1000 on a used trans, do $250 worth of work to it and install it (paying a shop $1000?) on a car like that.

One option is to pick up a parts car like this:
https://losangeles.craigslist.org/la...899580802.html

Put a few hundred into the trans: seals, filter and a TransGo Valve, then install it and see how long it lasts. The rest of the parts car could yield a few useful items or could be sold to recoup some costs.
A proper $4000 rebuilt trans plus install does not sound like a wise investment in a car worth maybe $2500 with a good working trans.

tozoM8

Some of that metal shavings are stuck on the input speed sensor that's why you have an implausible signal. The clutch A basket is broken and the bearing in front of the clutch C.

Weave

Thank you all for your replies. ... I considered a rebuilt unit but I’ve been quoted approx $1,300 for trans and $1,800 plus fluids & filter to R&R. I’m dropping it off Mon to trans shop and may just rebuild it fresh. I appreciate the info and direction. I’ll update you as I continue on

tozoM8

Some trans shop under quote to get you in and once they have your car apart suddenly it will need more parts.

jfrahm

If you are just swapping in a used trans put in a new lower valve body casting and a transgo valve and you'll stand a decent chance the trans will be OK for a long time. These are pretty easy to do and parts should be under $300.
If they are doing a rebuild also find out how the main pressure control valve will be addressed, some shops will just replace the broken and worn parts and not address why stuff broke.