rocky_mtn_a4

So while I was in our crawlspace installing a new floor drain for our boiler system, my wife hollered at me a couple of nights ago and said the air compressor for her 2006 A8 4.2 was running in the driveway with no key in the ignition...just randomly running. I thought to myself, I'll bet the relay finally went and was sticking, but I currently had the main drain to my house spliced into and the water was off, so I continued on with my plumbing adventure and as soon as I got the sewer line tied back up, I was going to go pull the dash and pull the relay...long story short, I forgot to and it ran presumably all night in turn killing the battery dead! Didn't notice until I went to get smokes the next morning and the key fob wouldn't work...so I used the key to manually get in the door. Like a goofball, I stuck the key in the ignition and the key got locked in the ignition so I freaked. Luckily it released as soon as power was applied to the cars battery and I thought all was relatively well. I had a friend pick me up a relay from Audi as they live WAY closer to the dealer than I do and they were headed to my house that afternoon. Charged the battery, replaced the relay, checked the fuse and all seemed okay. Did a VAG scan and had all sorts of jibbrish show up due to the loss of power. Group 34 does show some interesting stuff though. I will post that scan if there is any value that someone might find in it. My question is, now the suspension is acting awfully strange. Lights on the dash, front end is on the bump stops..yada yada yada...What can cause the voltage to the air compressor to NOT be applied besides the fuse being blown and the relay being bad? Applying 12 volts to the compressor connector yields a running, yet noisey compressor, but the signal is not being sent from the car to power the compressor. I also took the compressor out of the car and applied 12 volts and feel absolutely NO air coming from the outlet where the tan compression line was once attached before removal. I'm thinking / hoping that that stuck relay just burnt the compressors ability to produce any compressed air. I'm still stuck on why it won't send a 12 volt signal to start the compressor when the car is running or started. After I replaced the relay, the compressor did come on when starting the car, but was oddly loud as if it was pushing against a closed valve or something. It won't come on now unless I apply direct 12 volt power, and it produces no air output. If the solenoid, pressure, or temperature sensor has a fault, will that not allow the power to the compressor? Heres my address 34 scan last night right after the relay replacement, but before codes were cleared...

Address 34: Level Control Labels: 4E0-910-553.lbl
Part No SW: 4E0 910 553 H HW: 4E0 907 553 F
Component: LUFTFDR.-CDC H06 4480
Coding: 0015510
Shop #: WSC 02313 785 00200
VCID: 285506159B74140181-807C

6 Faults Found:
01772 - Signal from Level Control Pressure Sensor (G291)
008 - Implausible Signal - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 3
Fault Frequency: 7
Reset counter: 173
Mileage: 172786 km
Time Indication: 0
Date: 2017.02.03
Time: 10:23:45

01770 - Temperature Sensor for Level Control Pump/Compressor (G290)
007 - Short to Ground - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 3
Fault Frequency: 7
Reset counter: 173
Mileage: 172786 km
Time Indication: 0
Date: 2017.02.03
Time: 10:23:45

01397 - Venting Solenoid for Level Control (N111)
009 - Open or Short to Ground - Intermittent
Freeze Frame:
Fault Status: 00101001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 172
Mileage: 173614 km
Time Indication: 0
Date: 2017.02.17
Time: 00:19:31

01770 - Temperature Sensor for Level Control Pump/Compressor (G290)
010 - Open or Short to Plus - Intermittent
Freeze Frame:
Fault Status: 00101001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 172
Mileage: 173614 km
Time Indication: 0
Date: 2017.02.17
Time: 00:19:31

01399 - Relay for Level-Control Compressor (J403)
009 - Open or Short to Ground - Intermittent
Freeze Frame:
Fault Status: 00101001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 168
Mileage: 0 km
Time Indication: 0

01400 - Suspension Level Control
002 - Lower Limit Exceeded - Intermittent
Freeze Frame:
Fault Status: 00101001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 168
Mileage: 0 km
Time Indication: 0
__________________________________________________ _______________

I do have a more recent scan from today after I cleared codes and drove it a bit, I have tried bubble tests and have the entire fender well taken apart to bubble test the distribution block, but, I have no way of pressurizing the system without that compressor that I'm aware of. The car is on jack stands in the garage and the rear of the car is not affected. Do I try rebuilding the piston ring in the compressor to get compression, or is that futile because the solenoid, pressure, and/or temp sensor will keep it from powering on anyhow? Someone help a family man out? This is my wifes car and she relies on this for transporation for our special needs son to all of his 8 doctors appointments per week. Thank you for taking time to read this, and I have read until I'm exhausted using the search function, my problem just seems different than that of others.

New scan of address 34 after clearing codes and driving 10 miles or so at high speeds...

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Address 34: Level Control Labels: 4E0-910-553.lbl
Control Module Part Number: 4E0 910 553 H HW: 4E0 907 553 F
Component and/or Version: LUFTFDR.-CDC H06 4480
Software Coding: 0015510
Work Shop Code: WSC 02313 785 00200
VCID: 285506159B74140181-807C
3 Faults Found:

01400 - Suspension Level Control
002 - Lower Limit Exceeded - Intermittent
Freeze Frame:
Fault Status: 00100010
Fault Priority: 2
Fault Frequency: 1
Reset counter: 174
Mileage: 173630 km
Time Indication: 0
Date: 2017.02.18
Time: 18:10:58

01772 - Signal from Level Control Pressure Sensor (G291)
008 - Implausible Signal - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 3
Fault Frequency: 2
Reset counter: 174
Mileage: 173644 km
Time Indication: 0
Date: 2017.02.18
Time: 19:57:35

01583 - Leak in System Detected
000 - - - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 3
Fault Frequency: 2
Reset counter: 174
Mileage: 173644 km
Time Indication: 0
Date: 2017.02.18
Time: 19:57:35

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Jack88

You're problem may not be identical to the others but the troubleshooting is the same. Any one corner lower first? Did you do the soapy water test on the valve block?

rocky_mtn_a4

The car is in the raked or dynamic position. Low in the front I would presume as low as it will go. I bubble tested the compressor outlet and the valve block, but if the compressor has no output, there's nothing to leak. Both sides in the front are as low as they'll go. I'm thinking the relay sticking all night cooked the piston ring and it's lost compression. I just want to know if the solenoid, pressure and/or temp sensor can prevent power being sent to the compressor? The relay is new and the 40 amp fuse is in good proper condition with continuity. Something has stopped telling the compressor to energize as it will run with no problem hooked right up to 12 volts, it just has literally no output air.

Jack88

Okay, first step is to replace the compressor if it is no longer functioning. If your front is bottomed out, you have a leak somewhere. You won't be able to find it without a working compressor, though. Don't run the new compressor any more than is necessary for diagnosis, you don't want to burn out a second one.

rocky_mtn_a4

Fair enough. I'm going with one from ebay. There are a couple to choose from between just under $500 to just over $600. I just can't do $1200 from Arnott or ECS...I'll order it tonight. Thanks for your advice, I just wished I knew more about why the car won't send voltage to the supply connector for the compressor. Thanks again...

MP4.2+6.0

As w/ many of these posts, let me try to simplify to the most common scenario. The compressor running to point of burn out is most likely a symptom, not the issue. But it destroys an important and very expensive compressor component. Yes, a stuck/fried relay can do it too, but again the relay often fries to begin with from a compressor cycling on an off way too often.

What both have in common much of the time are leaks in the suspension the compressor is trying to make up for, literally working its guts out.

Net, need to get compressor working AND thoroughly test system for leaks. The latter predictably leads to problems with the former if you don't realize to act very quickly at first signs of leaks--sags, oft working compressor, more frequent up down arrows on dash, etc.

rocky_mtn_a4

Duly noted. I'm going to order the $625 compressor from ebay and install. After that I will go over the system with tons of bubble leak detector and look for one side to sag faster than the other. If I'm not mistaken, even if I can't visually notice a slow or small leak, VCDS "should" notify me with daily scans if a leak is detected or present, right? I'm just worried I won't be able to visually identify it unless it is like your experience mp4.2 where you saw 1 side obviously lower than the other. I'm hoping it was just the relay cooked the compressor, but I have no problems dropping $800 on a strut if it's leaking. Thanks guys! Once it comes in the mail I'll post back for posterity.

MP4.2+6.0

No, unfortunately you can not count on it to show codes for a leak. Some certainly report they have had them. I had none. And neither soap leak testing nor listening is a sure thing either. Both worth doing of course, and looking for corner specific codes. On mine in the end I had to rely on best judgment of one side seeming to come down slightly faster than other (in front), and a little more visible with first side seeming to bottom first. But mine leaked down for like a day plus, so akin to the proverbial watching paint dry. Proved correct, but was maybe a 90% or 95% best judgment. Not 100, nor 99.

ltooz_a6_a8_q7

If you hear the pump running without ignition on means the relay 373 might got stuck and shorted itself out. Before jumping to any conclusion, check it first. There is a video on YouTube describing how to fix it. I'm having suspension problem right now. I'll be fixing it after our ski trip. Check out my post in my signature.
Cheers,
Louis

rocky_mtn_a4

Relay 373 fused itself which was the original symptom. Replaced with newly remodeled OEM relay 645. That was first things first...my compressor will not energize now and the relay is good, along with the 40 amp fuse. If I supply the pump with 12 volts direct, it pumps, but no compressed air comes out. I've ordered a new compressor and should have it fixed Wednesday night. From there, I can successfully pressurize the system and check for leaks. I am still baffled why if the relay and fuse are good, something is telling that power supply wire to the pump not to energize. Maybe a faulty temp sensor on the pump, or bad signal from the solenoid. Not sure. We will see how the new pump reacts once installed. Thanks for the replies folks!