stigg

I thought my air suspension gave out when I saw the icon flashing and
the suspension indicator dropped to level 1 from the usual 2 I use.
When I parked and got out I heard a hiss from the left rear and the car was sitting low. However, after re-starting the engine the compressor run and the level went back to 2. My left rear is some half inch lower than the other corners but overall the car keeps the level, sinking only a fraction over a couple of days.
Anyway, today I was driving, all was all right but then I think after I went over some bump or pothole the suspension icon went on and green indicators started flashing and ended with level one light and solid suspension light. Pressing the up button did nothing and the car was sitting low, except right front which had some gap wheel to edge of well. After I re-started the engine, suspension went back to level 2, the height is the same, I know by using my gauge = four fingers. Before I start digging in, I thought I would ask the collective brain here.
Thanks,
Stan

amiram

Check for air leaks in air springs \ air pressure pipes .(soapy water test)

Worldwidebeagle

Agree with Amiram. Also check out with a VCDS for function as well. If the springs or pipes leak, the pump runs and runs - and then overheats. The compressor in ARs have a over heat - thermal shut off. VCDS will log that.

Repeated sinking is most likely a crease in the bag starting to go.

SeeksAR

Scan for errors from one of the ride height sensor(s). A flakey sensor could be affected by bad bumps and send erroneous height signals and the system will try to compensate.

But definitely try to rule out an air leak. MOST problems I've seen on this forum are form leaking bags. And most are on the front shocks (10:1)

A spray bottle filled with soapy mixture is your friend...spray around where you hear the noise and look for bubbles. Don't get your head squished in the wheel well while watching.

The most likely culprit is the rubber fabric on the airshock bag itself is leaking. Followed by the o-ring seal(s) at top or bottom of the shock. Followed by control valve body. Followed by an air line fitting at one of the junctions. Followed by a crack in an air line. And followed (last place) by a leaky pump.

If you haven't watched the shock in action, peek underneath while the car is raising or lowering. The airbag folds over on itself like a turtleneck shirt. It is usually at the crease where it folds over on itself that most of the leaks occur. And usually only at a specific ride height. When you set to the bad height, the air comes seeping out through the rubberized fabric like blood through a bandaid. But when you raise up above that height, the rubber flattens out and is compressed against the shock absorber, and prevents the air from leaking out.

That's why a lot of people don't understand that they don't have problems with leaky bags when they drive and park at Level3 and everything seems swell. But, on other days they find the car on it's haunches in the morning if they leave it at Level2 or Level1.

As mentioned above, the pump will go into thermal shutdown mode if it overheats trying to keep you at the set height. Turning the car off and then back on again may give it enough time to cool down and reset. The airtank in the left rear cargo area holds enough compressed air to raise the car a couple of levels without needing the pump to turn on. If the leak is constant at all heights, then the pump might never catch up to fill the shocks and the storage tank.

Go to the most obvious spot (sunken left rear corner ?) and spray away till you find the leak.

Worldwidebeagle

Great post SeeksAR.

IMHO, I have never seen a rear bag leak. They get a fraction of the wear and tear of the fronts. Would bet on front or control valve.

A decade ago, a Continental TEVES engineer told me the US has many more problems with leaking bags that in Europe. Particularly in the US, the allroads were most popular in states with harsh winters: Colorado and Minn. They guessed it was due to the use of sand and grit and gravel on our roads - the gravel/grit gets caught in the bag folds and wears it out - as you mentioned. He suggested, and I did this religiously, raise the car to 4 and power wash the bags to get off sand and mag chloride/salt every few weeks in the winter. Seems the mag chloride is sticky and holds the sand in the bag folds. Easy to do at the car wash since I am there weekly anyway in mucky Colorado winters. Had one OEM bag last more than 127k and still going strong.

indoor

Good theory on suspension wear(salt, and all that in the winter), but pretty much the same amount of salt and grime gets to the rear suspension. I know that because I wash the bags out too every time I wash the car. More sand in the back, but that's due to the texture of the wheel lining...

It's the heat from the engine that kills the front suspension. And it probably works in combination with salt and all that. And it happens mostly in the winter when the bag is exposed to high heat then very cold in a short amount of time.

I installed a different coolant sensor for the after run system(that activates the fans and coolant pump after car is shut off hot). And guess where the engine heat is going: some is evacuated out through the front of car(one fan is running in reverse mode); the rest of the heat goes to the wheel well(and bags) from main big fan going in normal mode. I held my hand in different areas of the front and could feel the heat coming out the areas described above Now the after run system only does this for 10 minutes. But when you drive it happens the whole time engine is hot. Also, why most noobs can't find the leaks: it's almost always toward the engine

Worldwidebeagle

Great information. I never thought about heat and it effect on the bags.

In my personal experience, the amount of sand, gravel and grit in Colorado winters is far more on the front suspension than rear. Yes, the woolly rear linings seem to soak in sand, but the amount of grit on the rear bags, rear control arms and rear knuckle was far far less for me. My front bags were caked and rear bags only a slight dusting.

I also did the lower temp after run sensor. Mixed blessing. Every time i parked the car, several people would come up to me and say: Mister, your car is still running. I hope it helped. My indie mechanic friend hated it. Said it killed batteries. I never had that issue.

SeeksAR

Both of my front bags leaked on the sides facing the engine.

stigg

It is the left rear that is the lowest. There must be some slow leaks, the car does go down slowly if not driven for several days. After all, the mileage is
over 320,000 km on Ontario roads so salt/grit abundant in winter and as far as I know the bags are original. Having said that, the suspension is quite stable
apart from those two instances which I described before. I can go to all 4 levels and don't get any sign of leaks or sinking on any corner.
Looking at the air diagram, I had a thought that maybe one of the valves leaked somehow when I went over the the bump and that was where the hiss came from, because if the bag leaked, it could not have sealed itself now.
BTW, where are the valves located? I was replacing the rusted compressor shield a couple of days ago and I saw a module where all the air lines enter but there is nothing at the wheel suspension.
Anyway, I will see how it develops, so far all is working ok.
I will try to get the bags washed and check for leaks with soapy water in various height positions.
Thank you for the good pointers.

stigg

It looks like the idea that there is a leak at a certain height applies to my case. I drove on a highway today and the car switched to level 1 but when I parked, the suspension icon started flashing, green level indicators too, but after a while it all stopped and the car was sitting low. As before, I shut the engine off, then on, then again, and after the 2-nd attempt the suspension started rising and ended up in level 2. On my way back, it happened again, flashing icon, low position, went back after a couple of restarts in the driveway and stays this way. I guess in level 1 position there is a leaking spot somewhere
which must be small enough for the compressor to be able to overcome the leak and pump up the bag, or bags, and so somehow seal the crack.
This scenario looks likely so, how would I go about finding the leak? Extended, the bags don't seem to leak, they leak when folded down and so the leak is probably inside the fold and I won't get the soap water there nor will I see the bubbles. I will be putting winter tires now so I will get access to all bags. What would be the best strategy to use in this situation? Now it occurred to me that the dead low position is probably lower than level 1 position so maybe when I experience this again, I could measure each corner and compare with level 1 height which should be around 405 mm if remember correctly, and the leaky bags will be where this measurement is less. Will the good bags stay at level 1 or will the self-levelling mechanism sink the corners to the same level?
Thanks for the input.
Stan