MP4.2+6.0

Looking for either confirming or different advice on suspension issue on my 2006 W12--now with family but I still look after the advanced stuff. Given to date experience w/ set up, pretty specific backgrounder here to move well past the easy conclusions of leak, obvious compressor, etc.

Background: Some weeks ago driver reports motor running sound after shut down. Records a video, which I play and recognize as compressor sound. Tell him to disconnect battery if needed but noise "goes away" on its own before he gets that far. I figure compressor fried. He brings it over.

First diagnostics beyond scanning:

• We go for the 10A fuse on passenger side panel. Checked as good.
• Took apart lower dash and checked 40A compressor fuse. Good.
• Pull compressor relay. Since new one on hand we change it out. I never actually tested old one, but prying it open I found some electrical type smoke residue like you see on older parts, and points did seem at least worn/affected. New relay installed and still there.

Closed up dash. Ordered new pump last weekend given no apparent run and the codes. One code was temp sensor overheat. Other one was the one below about short to ground.

Next diagnostic round today w/ new pump now in hand but still in box: Check codes and has the one below. Try to clear and it stays persistent each time. Pull fender liner to go for pump. Notice on W12 it is more stuffed in there, right below headlight.

Next and why we did not pull pump today nor end up swapping it out either. I hook power to the main power leads at connector on existing pump in place and it...runs. A little louder maybe than new one we got--supposedly a WABCO and has both box and parts sticker labeling on it that say that, but also some Miessler labeling, and a label on one half of assembly saying made in India and the other half saying made in Germany. The fact that the existing installed one runs still has me doubting whether it is bad. Paid about $450 for the pump unit. Avoided the mid $200 brand du jour stuff that came from who knows where in reality. We put car back together w/ no pump change so far, scratching our heads.

Re run VCDS yet again, still same code as below. Only code. Can't clear. All four MMI choices for suspension grayed out, though at start of session today and in prior weeks' diagnostics only lift and dynamic modes greyed out. Go for drive to see if it improves, especially when just yesterday with near new D4 S8 I found it needed a mile or so to get out of raise mode and return to normal height. Yep, by return on W12 to driveway the comfort and automatic modes do in fact return but not other two. Yellow warning light stays on. Still has same persistent code below and can't clear. Now run the VCDS diagnostics and it eventually reports fail--same as last week. But it continues to read all the corners height wise when I poked more today, and I can find a measuring block saying compressor temp at 45C. I do notice in diagnostic mode none of the corners ever drops at the points in test they should, and it is showing me sensors and heights on screen but no apparent movement/change. No compressor noise/running ever either. Odd thing to me though is still over a week in, car still holding air. If anything it looks a little high right now. Couldn't engage raise or jack mode, so even jacked up a corner to get at pump and no ill effects after dropping car back down. Causes me to wonder if maybe compressor might be eaking out a bit of run time still while driving. But not my drive any more, so can't be sure day to day how it is performing on road.

Question one: See code below. Given above diagnostics and that powered lead test actually runs existing compressor, do I conclude nonetheless it is probably toast (like the dislocated magnet stuff) and pulling too much load? Got tired and wanted to check in w/ board, but I have some hunch 40A fuse may now be fried if I spend the well over an hour again to pull apart lower dash to get at it and then reassemble. 10A fuse that's easy was rechecked and still good. Thus, theory would be pump is barely running but pulling high load, which probably toasted fuse. Could have happened post relay change last week when pump ran at some unknown point.

Question two: Any other new ideas? Vaguely wondering if valve block malfunction could be triggering a lot of pump running or the fact w/ diagnostic test height does not move. Yet, car is seeming to hold air just fine even never hearing pump cycle.

Any réponses from others who have been there against these diagnostics would help. Meantime I sent car off for some more road time since holding air. Default next step will be be eat the $450 on pump and change out (and thus now not returnable), plus reopen dash to check fuse again if code does not clear or new pump does not cycle.

Jack88

I haven't got experience with this issue, but it's worth mentioning checking all the associated wiring for deterioration. Good luck.

MainelyA8

I had something similar happen last winter. The valve block I had replaced was faulty, and ended up burning out the compressor. Oddly enough, the fuse had blown but the air system retained air for days with no signs of leaks. Luckily the compressor was replaced under warranty (with one fitting a similar description as yours) and I bit the bullet and installed an OEM valve block instead of a Miessler one. I replaced the compressor/valve block/fuse/relay and it solved the problem. It was suggested to me to clean the connectors when I was just producing electrical codes like yours. I remember being thoroughly confused as to how the air suspension was holding air without the compressor running. These systems sure can be weird sometimes.

ltooz_a6_a8_q7

I don't think it's the pump, it's the air suspension controller or the valve block. As I understand the valve block is used to control the dynamic suspension. To test the pump, very easy, release the air of the struts using 10mm open wrench. I don't know if you get your lift back, put it on lift as soon as you turn on the ignition, don't start the car, charge the battery.... you'll hear the pump and the car would raise just like one of my videos.
With the terminal 30, it's electrical. The valve block solenoids are bad. I would clean and check if the pump test passes.

Cheers,
Louis

jlbell

Before you do any outlandish repairs you might want to check: just so you know SB means: Fuses in fuse box, dash panel, left

MP4.2+6.0

Keep responses and suggestions coming. Thanks meantime.

I think my next steps will be:

1. Drop dash again and recheck fuse and (newly replaced) relay at the hidden panel. My relay is located where the earlier versions are--up high above knee area rather than down near floor area. Obviously if fuse is now found as blown (unlike last time pre relay change) then seems like compressor draw is excessive and probably move to replace compressor.

The more practical additional tests I am thinking at same time (and assuming fuse is fine) are:

1. Even w/ new relay, validate switching and continuity by powering relay switch and looking for continuity through terminal 30 side of it.

2. Check for power at the compressor relay port on the plug side. If power is not there, logically an issue electrically further upstream, like terminal 30 relay.

3. If power is there at relay base, then jumper from terminal 30 directly across--like the relay would do when switched. Since I have confirmed compressor operation at its main power plug, it should then run, correct? That is, I'm thinking the relay would normally get its signal from the controller to run the compressor. Just planning to run momentarily to validate power rather than long cycle time with potential for more air pressure in system that controls would not be calling for.

Anyone done testing like this? I will look at diagrams further.

jbell, also thanks for the reminder on terminal 30 relay. On W12 I think that may be the one that sits all by itself in the a waterproof plenum box to which one of the ECU's is attached on top. But notice in diagram it only talks about very early build D3's, and other times I have thought that is a relay that powers ECU's. I can look at Bentley more there too. It reminds me that at one point a few years ago there seemed to be a momentary flakiness there affecting the engine in some way and causing an inst. panel light show--to point I bought the relay--again the only one in the box on a W12 even though diagram shows multiple positions for relays. Never installed though since it seemed to be a one time hiccup, but I should probably backtrack to that now.

MP4.2+6.0

Question: what year were you pulling those diagrams from? I have been all through Bentley and just can't find a J317 terminal relay, for 2006 or even others I tried to scan. There is a terminal 15 relay in a variety of them, which is on same relay panel as air compressor but in upper right position. The diagrams I look at for 2006 seem to just show the relay being supplied by terminal 30 power that just comes off wiring harness in general. Audi wiring nomenclature is terminal 30 = unswitched (main battery) power and 15 is switched IIRC. Notice the engine codes in that 1.1.1 diagram are unfamiliar, at least to me (W12 is BSB). Plus that box location and content moves around some on 4.2 vs. W12 I think--physically moving due to them shoehorning in the second W12 ECU. Meantime thanks for poking at it; just trying to pin down where I probe next electrically. Per my other other general reply this morning I plan to explore whether compressor relay either has power or is feeding it by working off relay plug/connector.

I also understand now the small fuse in the right hand dash panel is what powers the suspension control unit (box under dash under MMI controller IIRC), while 40A fuse is the main one for pump. Since MMI is displaying some parameters of suspension choices, seems like my power questions remain around pump--including if it is ever getting a signal from the control unit that activates the relay switching from the diagrams I reviewed. May still have electronic issues at control unit or the valve block (from diagrams it looks like signals to air shocks pass through block too?), but first I want to confirm the obvious--getting power to pump.

BTW Louis, thanks on your ideas and thoughts on valve block. I want to run pump by bypass if possible rather than try to force it by pulling air line because suspension is still inflated and car drivable. It comes from current SJ home to MP for me to look at, and if it drops we are pretty stuck.

ltooz_a6_a8_q7

MP4-
I've been busy making a video on TV tuner.
To me, the system consists of too many components in a closed loop control system as I understand. If I can eliminate any independent component out of the system, I would do it first regardless. BTW, I did drive from Morgan Hills, to Santa Teresa and back to Fremont with the bags on the bottom at 60-70 miles.
Now, since I started to have all the problems like everyone here, I realized something, it's not as everyone think or thought about all the presumed dead conditions.
The components protection on A8 is amazing. My air pump should be dead by the time I got home if it wasn't turned off by the system.
If your suspension is air tight, it should pump it right up, if the pump can't be turned on by the system, you can pump it manually, either way your family can still go home. At least, you know it's the system and not the pump. Another less thing to worry about, IMO.
Now, for some reasons, the system doesn't turn the pump on because it senses something, you have a brand new one, start measuring all connectors to see which pins are NOT correct, if all of them are the same, then the system senses somewhere else.
Cheers,
Louis

ltooz_a6_a8_q7

After reading everything, I think it's the valve block since the options come and go. The pump was never activated since the ride height is high, the pressure release valve doesn't work, hence the system couldn't go to lower height modes.
Reset everything and hope it reset the system and release whatever the system turned off.

MP4.2+6.0

Thanks. The one contra there is it won't lift either. Both lift and dynamic (drop) are grayed out. I am keeping valve block in mind though, esp. if I find I can activate pump at relay plug via jumping. That would leave me thinking either valve block or control module. I recall almost no posts on control module, especially here where display suggests it has at least some functionality or at least communication over to MMI.