BS_Smith

A month since last report--"my, how time flies."

Not much to tell; certainly nothing definitive. Main activity was fairly comprehensive leak detection: car on lift, all wheels off, all liners pulled, leak detection fluid on all accessible suspension components and lines--but no trouble found.

Still throwing "Signal from Level Control Pressure Sensor (G291)" as the only suspension code. For inspiration, read almost all AW's 150 threads with occurrence of "G291". A trail of woe for sure but to my reading, no instance where a leaky control valve/block was determined to be the cause of one corner of the car dropping. Yet when I get ready replace more parts, that's where I'll start. One point confirmed in leak detection was that the RF indeed recently had been replaced by the previous owner. It looks new, top to bottom, including a shiny "Continental" label. Tough to believe a less than year old, less than 2k, quality strut has failed, particularly when leak detection gives no evidence that it has. Not impossible of course, but not likely.

Meanwhile, the vehicle will drop to stops if left unused, at a rate about the same as previously reported; e.g., 28 Apr - 1 May: LF 28 1/2" to 27 7/8"; RF 28 1/2" 27". But at least with current usage, struts reinflate from accumulator before drive off. So arguably, the compressor is not getting undue workout at present.

The plan is to monitor codes and be goaded into action if the compressor overheats. Perhaps because of a strong USD, parts prices don't seem as painful as previously thought.

Miessler currently is selling the suspension control valve (4F0616013) on eBay UK for GBP 129 (USD 190) plus shipping. Miessler's webpage (where the Euro price is a bit more) shows shipping would be EUR 47 (USD 55), so about $245 delivered--even better if Miessler doesn't charge US customers the 19 percent VAT included in the price. Or simply pay $269 to Miessler's FL eBay seller. Miessler states the part is German-made and fully compatible, and gives a two year warranty. They seem a decent supplier.

If replacing the control valve doesn't solve the problem, then the nearly new strut must be leaking, so I'll replace the spring portion of the strut with Miessler's--EUR 299 (USD 345) on their website.

And if at the end of all this, the compressor is a casualty, will try Miessler's 4E0616007B (GBP 259/USD 380) rather than their WABCO unit (EUR 589/(USD 675).

At least that's how it looks from here.

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Public service announcement: somebody buy these mats (eBay item 282016492277)! Audi winter mats were my first purchase for the A8--and I had trouble finding them. No longer available new anywhere, US or Europe. Finally found a like-new set on eBay for a bit more than this seller is asking. I love them. Have a set for the A6, another for Mrs' A3. Son got a set for Christmas for his A4. Grab 'em while you can!

Hannibalacp82

You asked a question on the global clear codes button not clearing all of the codes. I noticed that on my 2008 S8 as well and have resigned myself to clear the codes via each module one at a time.

mannyo1221

When I had the same G291 code more than 2 years ago the cause was the compressor. Basically the car was requesting a certain air pressure and the compressor could not supply it. Result was the G291 code and the compressor running more often as the car attempts to maintain the air pressure requested whilst driving.

I had the compressor rebuilt using the bagpipingandy kit from ebay more than 2 years ago and have never seen the G291 code since.

Before rebuild it would take a considerable time to go from Dynamic to Lift height, now it takes less than 30 seconds.

My 2004 D3 has of late had little use, however even after leaving it for 4 days the suspension height is as when left.

MP4.2+6.0

This is correct from my experience too. I do a global clear first, then a quick auto scan again. I abort the auto scan as soon as the summary screen shows up--like after the ECU 01 scan--to avoid the 20 min delay for that to go thru module by module. It captures which have errors in that summary screen in the first 60 seconds or so. Then I just remember, write down or snap a pic of the summary screen. I go into the relevant modules and clear those, taking a pic of anything I want t track for later. For me, the usual are the who cares power codes sprinkled here and there, the typical occasional Nav misread, and a supposed door handle that seems to work well enough. Of course I pay attention to any that affect a function. Recently found a bad rear HVAC head that way, and as the driver would not have noticed for a long time, if ever.

carl viking

Two small comments to follow on this for OP.
First, there is a measurement block in VCDS where you can see the pressure from the compressor. I believe it's rated at 15 bar. Running the compressor and looking at that block, you can see if the compressor is delivering enough pressure.

Second - if I leave my car for 3-5 days there is zero drop, as LONG AS THE TEMPERATURE STAYS CONSTANT (or close to it). If I leave a garage in the winter, leave the car parked overnight outside and temp drops or it is cold outside (as in below freezing and esp when zero or colder), the car will drop a few inches.
As soon as I unlock the car the compressor immediately brings it back up. If you read the attachment from Mishar, you will see that the system is supposed to turn itself on to check levels after a certain amount of time, which i assume it does. I have never been able to figure out if the decrease in volume of the air is what makes it drops when it gets colder, or (more likely) the rubber bellows loose flexibility in the cold and small cracks then release pressure.
I spent time chasing this early on, and even contemplated replacing the rear shocks ($$$ since there are no rebuilds), until spring came around and the problem disappeared. I now simply accept this "feature" and either check on the car if parked outside in the cold every other day or so, or just leave it in the garage those super cold days.

the_duke

My car will sometimes drop overnight if there is a big temperature swing. We get those often (90 during the day an down to 40 at night).

BS_Smith

Thanks for the comments.

Regarding code clear, yes, eventually I figured out sterner measures were required to delete persistent codes. One would think Ross-Tech could do by machine what now needs to be done by hand, but it's not too onerous.

Regarding the suspension drop, yes again, I've noted reported instances where replacing the compressor solved a G291 code. But I believe in my case there's a problem beyond a weak compressor, if indeed it is weak. Before replacing the LF strut, that corner dropped more than the right. After LF replacement, the RF drops faster and farther than the left. There must be a leak somewhere in the RF portion of the system.

Unfortunately, I'm unaware of any way to monitor compressor pressure via VCDS. According to:

Audi Resource - Level Control

the only pressure monitoring in level control module 34 is measured value block 006, which gives the pressure sensor signal in bar. But according to the self study program helpfully provided by Mr Misha, the only pressure sender/sensor is our friend G291 in the solenoid valve block, and "the pressure sender measures the pressure of the front and rear axle struts or the accumulator"--not the compressor directly. Oh, well... (If I'm misreading, please redirect me.) In any event, I believe a weak compressor would be the result of my drop problem, not the cause of it.

I also don't believe, in my case, the problem is ambient temperature related. The car is garaged. Outside temps generally have remained within a 20F band of late, and the problem has persisted. (An aside: in this land of low real estate values, we enjoy an attached three car garage. Yet the three cars inside, A8L included, are more show than go, while the working transport lives outside. News flash!--this is not particularly sensible...)

When the suspension problem worsens to the point I'm motivated to solve it, a fellow at Ross-Tech has suggested an interesting diagnostic:

Air ride suspension leak testing, may have a new method here....

that I believe I learned about on AW--but have forgotten where and can't find the reference. Apologies to the source. I'm no more eager to cut and splice pneumatic lines than others are to wiring, but it seems worthwhile testing.

Meanwhile, I pursue trivial matters. Looking way ahead, decided to get a set of winter tires/wheels now. And in the great big-little debate, voted for little, at least for winters (car came with 19s). 17" also was TireRack's preferred fitment for winter. Was able to buy locally a set of OE forged five arm 17s from an '02 D2--$175. Nice on the outside; nasty the other, but all clean now. Set of closeout Pirelli WinterEdge from TireRack at $97 per. After rebate, less than $400 delivered. Good enough for me. (Will get TPMS closer to time of need.)

Earlier, grabbed an eBay Audi pen to replace the one missing in my owner's manual folder. (I assume the car came with something branded, no?) While searching for that, eBay suggested a paint pen set--base coat in the car's color; the second in clear. First time I used paint pens (in the past, have used a small brush from factory touch-up kits, and less successfully, dabs with a Q-tip or toothpick from a paint can. The paint pens worked quite nicely to touch up small chips on the nose.

BS

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My original message, prepared offline, repeatedly was truncated after "After rebate," in the penultimate para when pasted in. Max numbers of characters exceeded? Or simply overflowed the BORING buffer? But then remembering posters' pages of VCSD scans figured it had to be something else. So, changed the LT symbol in the source to the spelled out text above and--problem solved (at least this one!).

BS_Smith

Reference to earlier postings in this thread will indicate that soon after purchase, the LF strut was replaced with a new, not remanned, Arnott strut. (This happened before it was clear Arnott didn't include active dampening in their new struts.) The new strut lessened but didn't eliminate suspension leak down. Leak testing was unsuccessful, the RF strut had been replaced by the previous owner nine months and 2k mi before I purchased the car, and I was relectant to believe the PO's $1200 strut could have already gone bad.

Because the car is very occasionally used, I decided to do nothing so long as there were no compressor overheat codes. But that code happened a couple months ago, and I finally decided to replace the RF strut, again with a new Arnott. While I'd prefer the active dampening Audi provided, in the time I've owned the car, it had one active front strut, and one dumb one--and I never noticed the discrepancy. How bad could two (some might say three) dummies be? I remain concerned about buying someone else's unknown mileage remanufactured unit, and wasn't prepared to pay for two new OE struts.

The deciding factor in electing to replace the RF strut and to replace it with a new Arnott was price. I was able to get the RF for $600 shipping included from True Blue Parts. (A year ago I paid $784 + shipping for the LF from Arnott themselves.) And if I get around to it, Arnott will pay $75 for return of the old strut. At $600 it was truly, "why not try?"

And the good news is, the new strut fixed the leak. For the first time since vehicle purchase, "it's up and it's good!"

The surprising news on this issue was that once off the car, I could see that the old RF strut also was an Arnott, a remanufactured unit. I hope their new struts last longer! (The previous owner's receipt from the shop that did the work didn't indicate that the strut they charged $1200 for--plus $500 installation!-was a remanned unit; only the OE part number was shown. Rascals!)

Despite past suspension frustration, the car has been a satisfying purchase. Took it with the Mrs on a trip to Maine last fall. Fast freeway flying most of the way; received knowing waves from a couple fellow A8 owners on the Mass Turnpike. Did the return trip non-stop--no fuel, no food, no restroom--and the trip odometer showed 600.0 mi when we reached home. It's a superlative road car.

btw--the 17" OE wheels and winter tires worked well as well. The comparatively small rims were tight but fit; the installer mounted wheel weights on the outside to ensure sufficient clearance.

All's not been completely rosy of course. A couple months ago, when the car was taken to the local shop for state inspection and oil change, they found a large oil leak. (Previously, there'd been no evidence.) The shop expected the leak was a failed crankshaft seal. They were reluctant to do the work and suggested Audi deal with it. I persuaded them to take it on.

As it turned out after replacement, the crankshaft seal wasn't the problem. Further investigation suggested the figure 8-shaped gasket at the base of the oil filter housing was the cause and after pulling the intake manifold, the valley was filled with oil, and weep holes for it to run out the front of engine apparent. With the intake off it also was clear the valves were FSI-gunked up, so they were cleaned as well. The shop was very gentle in their bill for the work, and they continue to make ownership of car feasible for me.

Although a regular AW reader before vehicle purchase, now I only jump in on a need-to-know basis. What once was entertaining reading, now is too stressful! (I note in a current separate thread, MP is wrestling with a suspension problem. Perhaps these cars aren't for mere mortals!)

BS
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2007 A8L 4.2

richard-tx

Please note that the "NEW" Arnott struts do NOT have any electrical damping control. The end result is that no matter what sort of ride setting you select, you only get what Arnott has set in the strut. Yes the ride height changes using the MMI controls, but the ride quality does not.

If it were mine, I would return the new one for a rebuilt with the proper electrically controlled damping.

BS_Smith

Thanks, Richard. As I attempted to convey in my post, I've been aware of the neutered nature of Arnott's new struts since they made this limitation clear to all, which was some time after I'd bought my first one. Perhaps more tenacious fellows than I could have persuaded Arnott to refund fully my then installed and used strut, but I didn't attempt it.

When it came time to replace the second unit, for reasons outlined in the above post, I again went with new Arnott. To recap, I'd been unable to discern difficulty with what should have been a seriously screwed up suspension--dumb new Arnott LF; active remanned (and failing) Arnott RF. Admittedly, I may not be the most perceptive guy around, but figured two dumb struts could be only better than what I had. For me, "all new but incomplete" was a superior option to "rebuilt old OE." Wouldn't expect all to see it this way, and certainly wouldn't want to come across as an Arnott cheerleader--I continue to believe their marketing of the new units is near duplicitous--but that's how I made my decision.