Air suspension faults and uneven height side to side
 

04 CTT 119k miles

I know there are tons of "my air suspension doesn't work" threads, but digging through them i still have some questions.
When I first got the cayenne a little over 70k miles ago, i would occasionally get the yellow/orange suspension workshop warning, i put in a new compressor piston ring and that went away. Recently I'm getting not only the yellow, but also a red warning. It doesn't happen every drive, but the frequency is increasing. It seems to occur most often right after startup or on the highway when it is auto dropping or raising based on speed.

running VCDS (i don't have durametric ) I get the following:
Address 34: Level Control Labels: 7Lx-907-553-34.clb
Part No: 7L0 907 553 F
Component: LUFTFDR.-CDC- 3C3P1 3081
Coding: 0015511
Shop #: WSC 128452 000 00000
VCID: 36621E4442477CF660-5178

1 Fault Found:
01400 - Suspension Level Control
001 - Upper Limit Exceeded

I think this upper limit exceeded is the common error when the compressor can't deliverer the required pressure/volume, which i would guess would mean either a leak somewhere, bad compressor, or it needs a rebuild again. the new ring i put on last time was advertised as a permanent solution better than stock. perhaps that was not the case?

before i go down the rebuild kit route (even though it is pretty cheap) is there anything else i should test?short of looking at every measuring block and figuring out what the spec is for the sensor it's measuring, is there something in particular?

the suspension does go up and down, although takes a very long time to drop below normal. I set it to sepc. terrain last night, measured it, then measured it again this morning and there was no drop in height. I did notice something that perhaps is unrelated however:
first i sanity checked myself by ensuring my garage floor is level, which it is side to side (slight slope front to back as expected)
measuring from the floor to the bottom of the center of the fender arch
in spec terrain height, the passenger side of the car in both front and rear is 1/8" lower than the drivers side at the respective corners.
at normal height, the pass side is 1" lower both front and rear.
at both ride heights I put a level on the top of the rear bumper and it indicated the vehicle was sitting dead level!
the tires are brand new less than 100 miles and inflated properly/even side to side. I do have a full tank of gas, i'm not sure if the tank placement is biased to the right? I can't imagine that the car would be designed to sag 1" do to driver weight? I'm also not quite sure how with varying differences in height based on ride height but the car is still level side to side is possible, but bubble levels don't usually lie :)

Bodies aren't always perfect on cars. Suspension measurements should be taken from chassis points rather than measured from the fenders, to really have good data about the heights at the 4 corners, but a 1" difference would be pretty large, regardless.

I agree, can't use fender measurements to the ground to determine ride height. Have to use a hard chassis point... like the jacking points.

Perhaps the "upper limit reached" message means something different this time... sounds like you fixed the compressor OK and sounds like there aren't any leaks in the system since there's no overnight loss of height. So how does the vehicle know that the upper limit was reached? Some sort of sensor somewhere? Does it mean suspension travel limit reached or does it mean air pressure upper limit reached? If it refers to suspension travel, perhaps there is a sensor issue somewhere. If it is air pressure limit reached... hmmm, nothing obvious comes to mind, but seems unlikely you have a compressor problem.

going to take a look at it again tomorrow but you can hear the compressor running for a longer than usual time..

FWIW - IIRC - the factory suspension measurements include a measurement from the center of the wheel to the edge of the fender opening. I can't imagine a body where the two fenders are out of alignment by 1" wouldn't be quite obvious. Doing this measurement eliminates sloped pavement, different inflation pressures on the tires, etc.

i found an extra compressor piston ring laying around so i swapped that in this morning, it's running a little quieter, but still seeing issues. the brown line that enters the back of the compressor wasn't seated all the way in the 90deg fitting, so i snugged that up. still on a test drive it went from spec terrain>terrain> normal fine, then hung at low level selected for a few minutes followed by the red workshop warning. i stopped shut the car off and back on, and hitting the up control and got the accumulator charging message.. for the next few minutes i would get the same each time i tried. so it seems like the pressure tank isn't charging quick enough? so an issue either with the compressor or a leak somewhere in the line from compressor to the tank?

Well, it's not a big compressor. Moving the suspension up and down a lot will heat it up. It has an over temp shutdown.

I'm thinking that's where the 'accumulator charging' message comes from. Could be where the other warning is coming from too.

got my scan tool working again (the adapter i used to get the k line correct had some bad connections) now i had 2 faults:
01400 - Suspension Level Control
001 - Upper Limit Exceeded - Intermittent
02250 - Function Deactivation; Valve Duty Cycle
001 - Upper Limit Exceeded - Intermittent
reset the faults,
car was in low, i set it to normal which it achieved correctly once in normal height i took these readings: car was on a slight angle in my driveway
https://cimg7.ibsrv.net/gimg/rennlis...40c9e473a6.jpg
not that i really know what i'm looking at, but nothing seems that unusual to me?
after this i switched it to low and got the same error(s)

decided to try some live logging today on my way to work. cleared all the codes (just the first one appeared this time) lowered the car from normal to low. everything looked normal to me. compressor ran until it got just under 200 deg and shut off. pressure in the pressure tank ranged from 6-8bar. drove about 1/2 mile down the street and the error came back. i noticed the pressure tank was now at 0 bar. Which leads me to believe that there is either a leak somewhere on the exit side of the tank or the sensor is bad. if there was a leak on the input side, i don't think it would ever fill? since it is intermittent, a leak seem less likely to me pointing to possible a bad pressure sensor for the tank? does that seem like the reasonable next step? although if the sensor was bad i would think i would be getting the implausible signal code?

does anyone know the pressure range for the the pressure tank? ------edit: for those who migth look at this later, arnott says the system can have up to 10bar of pressure. so 8 sounds in range
for the touareg this says "The maximum pressure of the accumulators is 16.5 bar. If the pressure in the accumulators falls below 11 bar, the compressor starts and adjusts the vehicle to the set level."
http://www.volkspage.net/technik/ssp/ssp/SSP_302.PDF

but the highest i've seen is just over 8bar.. and the compressor isn't always running.

any ideas why the n111 discharge valve would be opening even though the tank has low pressure?

https://cimg6.ibsrv.net/gimg/rennlis...a7d1aec1ea.png

Sounds like a sensor problem.

just incase someone is searching and comes across this thread, here's the follow up...

after seeing this thread: https://rennlist.com/forums/cayenne-...ompressor.html
i decided to give the piston ring thing one more shot. the first 2 replacement ones i used were that x8r brand. the first i got off amazon and it lasted a little over 60k miles. the 2nd was also an x8r i got off ebay. i gave it a shot because it was very cheap this time (i paid $18 shipped i think) this one didn't work at all or maybe a super slight improvement. i went ahead and ordered the bag pipe andy version for $47 shipped off ebay and this fixed the problem straight away. the material used for the ring on the bpa version is very different.