PaulW

Subtitled (Martin is his name) came by my place yesterday to have a look at his tranny problems. We spent a few hours looking at it, putting some euro corner and side marer lights on Richard's (another lister) A8 and having lunch. Audi's seem to be a nice way to meet nice people.

I would not say that Martin's problem is a tranny problem, but a problem with the drivetrain and after pulling codes, the throttle position indictor.

Symptoms of the problem:

When the car is put into gear with the foot on the brake, there is a "clunk" that can be heard and felt. If it is put in drive, then back to reverse, then to drive again, it clunks every time. This is one problem.

The second problem is when driving the car around very slowly, and just putting the gas on lightly and lifting again, the car lurches as if somebody is pressing the gas hard. Also, when it is shifted into TIP mode, and you are slowing down, once it shifts into first gear it really lurches forward and has a "clunk" in the drive train.

The first thing we did was to hook my computer up to the car and pull the codes, the tranny had two fault codes:

Transmission Codes:
2 DTC's Found:
18169 - Shift Lock (N110): Short to Ground
35-10 - - - Intermittent
18264 - Throttle Potentiometer (G69): Error Message from ECU
35-10 - - - Intermittent

The shift lock is working correctly, and the two positions of the shift lock are either on or off, depending if your foot is on the brake or not. I did not clear the code because I want the dealer to see it. If they replaced the tranny and some wires touched where they shouldn't of during installation, maybe this code could have been produced. Regardless, I don't think it has anything to do with his problems.

The second was the throttle potentiometer (or throttle position indicator as it is written in the Bently). At first I thought that it was odd that the tranny would see this.

After searching the Bently and looking at things, the following items are transferred from the ECU (engine control unit) to the TCU (transmission control unit):

1. Engine speed
2. Engine coolant temperature
3. Throttle position
4. Vehicle speed sensor signal from instrument cluster
5. Engine torque (actual torque)

There were a couple reasons why the TCU could get the throttle position indicator code including a bad TCU, but one was that the actual TPI (throttle position indicator) was bad. This information is transferred from the ECU to the TCU through the CAN-bus wire data exchange. So that's how they talk to each other. So I got the great idea to search for codes on the engine.

Engine codes were as follows:

1 DTC's Found:
16505 - Throttle Position Sensor (G69): Implausible Signal
35-10 - - - Intermittent

It sure made sense now that the TPI was bad, and it is intermittent. Martin complains that the longer the engine is on (warmer it gets) the worse off it is, even when the ambient temperature is higher, it is worse.

If the TPI is bad, I would not be surprised if it is thermally affected. As it gets warmer, it has more and more error.

I did not have time to do the resistance checks of the TPI, the engine plastic has to come off, and TPI is right near the firewall. Should be very easy to check with a multimeter.

So this could be the source of his problem with the car lurching at very low gas pedal efforts, the ECU is getting bad info on the throttle position. Regardless, it is my opinion that it is the first thing that needs to fixed before additional troubleshooting should or can be performed.

I then got under his car while he went and put it in drive and then reverse and back to drive. It sure sounds like there is a bad CV joint, driveshaft universal (or CV joint whatever it has) or loose mount (like the torque support mount on the front of the engine or maybe a driveshaft bearing support).

When looking at the exhaust system going from drive to reverse and back again, it moved vertically about ½" to as much as 1". I do not know what would be normal, but it sure looked like too much movement to me.

So the thumping noise that Martin is hearing is the loose component (CV joint, torque mount, etc.) swapping from the "drive side" to the "coast side" when a reversal in torque is applied on the bad component. This also needs to be found and fixed. If the ECU is getting improper data from the TPI and putting too much gas into the system, this will be noticeable at low engine loads (slow speeds, just about coasting) causing a relatively large torque input into the drive train. This combined with the loose component, is causing the undesirable "transmission problems" that Martin is describing. I don't think it has anything to do with the transmission, just the drive train.

So my conclusion is as follows:

1. Before doing anything else, the TPI ECU fault must be cleared. This will require either replacement of the TPI or recalibration (there is some adjustment in the Bently but didn't read it in detail). This is required to move forward in solving the problem.
2. Clear the brake switch fault code and see if it comes back. If not, maybe it was shorted to ground during the new transmission installation, not a problem.
3. Check the drive shaft, all axle CV joints, engine mounts, transmission mounts, torque support, etc. for looseness. This would be relatively easy to do on a lift with two people. Repair as necessary.

After this is complete, Martin should have a tight A8 again!

Does this sound reasonable? Other input is greatly appreciated.

I can't believe the car has fault codes and the tranny was replaced by the dealer. It doesn't seem that they did a very good job in troubleshooting it. The first thing I would do is to check for codes. Quite frankly, I was very surprised that it had fault codes! The neat thing about this was I did almost all of my troubleshooting sitting in the passenger seat with my PC.

Here's a few pictures of Richard's car, he also lives in Oak Park, came over to pick up his euro clear corners and side markers. He has 19" BBS wheels.

pw

Richard's Car before Clear Corner and Side Markers with dirty wheels:

<img src="http://www.pccchicago.com/images/paul/DSC04996.JPG">

Here it is afterwards (and after a quick car wash) with Martin's car in the background. Looks awesome Richard, just where do you get those chrome mirrors? My car was on the other side of the street, not available for the picture shoot.

<img src="http://www.pccchicago.com/images/paul/DSC05000.JPG">

<img src="http://www.pccchicago.com/images/paul/DSC05001.JPG">

<img src="http://www.pccchicago.com/images/paul/DSC05002.JPG">

April

Good write-up. Also check A6 - Stoney's FAQ. Might be more info.

PlainRuss

Hi Paul,
Martin has contacted me about his vehicle and directed me to your post. I agree that the TPS fault should be adressed first. I am sure you are aware that the TPS is part of the throttle body and (at least from a factory part stand point) is not available by itself.
As far as the trans replacement goes, AoA does not allow a dealer to just replace a trans for any reason. Any trans complaints need to be reported to tech line first. A report gets filled out by the tech and a copy of the R.O. sent via fax to the tech line advisor. After this takes place other tests may be requested by tech line for more data to be collected. Tech line makes the decision as to what the repair will be. A authorization number is issued and then the tech can proceed. If this isn't done, Audi bounces the claim. What this boils down to is, Audi doesn't let the tech diagnose trans complaints. While that may seem like a good idea, often times it creates problems as it can be hard to get a tech line advisor to fully understand what a trans maybe doing via phone. I don't recall what state the tech line HQ is in but I do know it's in a different time zone. So getting the person to "feel" it isn't an option.
You did the right thing by not clearing the faults. This will at least give one of the tech's the chance to see what else is going on with the car.
Martin, I hope this gets taken care of for you. If there is anything I can do to help, let me know.