fallacious

My air suspension was leaking overnight and in the morning it would be super low, and if I try to lift it up it would say "Not Possible" or sometimes even "Chassis Failure." After paying ~$1900 for an indy to diagnose and fix the problem, they decided to replace the rear air spring bag, only to find out that it didn't solve the problem. They gave a pretty weaselly reason as to why they suspected that bag was leaking, and at this point I give it 50/50 as to whether or not that one was actually leaking. I brought it back to them, and then they recommended I replace the other bags too. I wasn't going to pay them more money for guesswork, especially since they were charging more per hour than my certified A&P aircraft mechanic, and with such rates I expect a definitive diagnosis.

Well here's my guide to narrow down where an air leak is coming from:

Note: If your air suspension says "not possible" when you try to lift it up, then that probably means you have an air leak somewhere in your system. If you start the engine and drive it for long enough, then it may or may not eventually bring enough outside air into the system to enable function. Yes even though it is advertised as a "closed loop" system, if the air tank (they call it an "accumulator") gets low enough the air compressor still has a circuit to bring outside air in, and has a drier inside to dry out the air.

1) Drive the car long enough to be able to raise the air suspension, and lift it as high as possible.
2) Turn the car off and put the suspension into "Jack Mode" by pressing & holding the suspension button UP for 10 seconds. The arrows should be blinking red. This isolates the bags from the rest of the system so you can determine which one is leaking. (note: the car must be on the ground so that pressure is in the bag. If done on a lift this may not work)
3) For each wheel, measure the current distance from the center of your wheel center cap to the top of the fender well, and write it down.
4) Wait a couple hours or even overnight and see if any of the sides are sagging.
5) If it's coming from one of your air bags, then one of them should be lower. Now you know which side, but not necessarily the actual cause. It could be: (a) the bag itself has a leak in the rubber, (b) the line / fitting coming into the bag, (c) the top mount of the bag
6) Pour some thick concentrated dish soap into a spray bottle (Palmolive is my choice) and fill it up 1/3rd way with water, and shake the hell out of the bottle.
7) Heavily blast the bag with the soapy water spray. Spray the fitting first. Then the top mount. In my case, it was the top mount, and you should see something like this:

Air bubbles from the top:

More air bubbles from the bottom:

Don't let some lazy mechanic tell you that it's impossible to prove that air bag is leaking with soapy water, or that it is a "slow leak."

Part number for the line valve fitting: 958-358-720-00 (~$100.00)

In my case, it was the front right side, and it was top mount that was leaking. There are 2 parts to change out:
958-343-018-20 (top shock mount ~$40.00)
N-903-677-01 (O-Ring ~$5.00)

There are many videos on YouTube on how to remove the strut itself from the car, so I didn't make my own. Look up the Bilstein videos. However, one problem I ran into was how to separate the front air bag from the shock absorber. On other models (Audi, Touareg) you can take the nut off that holds them together with a socket. But on the Cayenne the shock has a wire coming out. I had to grind down a deep offset 21mm wrench to get it to fit inside the groove:




Then I had to cut the wire to slide the mount & o-ring off, and solder/splice the wire back together later. This makes it a $45 repair, rather than a $1000-2000 repair. I couldn't figure out any other way to get the mount and O-ring off, so if someone else knows a way please post.

Also if anyone knows a good setup to fill the accumulator with nitrogen, please post the setup. Right now I just had the car refill the system with air and it's working fine, but I'd like to get some nitrogen in it sooner or later.

Hope this helps someone out there. I just hate getting ripped off by lazy mechanics.

garrett376

If you ever have to choose randomly, bet on the front right strut as the point of failure!

deilenberger

Some worthwhile reading:
https://rennlist.com/forums/cayenne-...defeat-it.html
https://rennlist.com/forums/cayenne-...pension-2.html
https://rennlist.com/forums/cayenne-...oing-up-5.html