DiagnosisUnknown

I have an unusual suspension problem and I need some advice from those with expertise. It emerged after replacing the front struts due to leaks in their air bags. I had the service done at the dealership with rebuilt parts. At the time of the switch they also checked the compressor and said it was operating normally. When I got the car back I noticed that it was leaning to the passenger side. I check whether they had re-calibrated the suspension after the switch and they said they hadn't. After they calibrated it the same issue was there. I calibrated it myself with VCDS after that. Same issue persisted.



Full Issue description: When parked with the car turned off or parked and running the rear passenger side sits approximately 1 CM lower than the rear drivers side with suspension in automatic mode. The front passenger side sits approximately ½ CM lower in the same conditions. When in lift mode the rear passenger side is approximately ½ CM lower than the rear drivers side. These measurements are consistent irrespective of time from last start. In other words it does not appear that there is an air leak. The car feels like it is leaning while driving so it does not correct itself when in motion. There are no lights on in the dash indicating any problems. The car suspension raises and lowers normally without issue. There are no abnormal noises from the suspension or compressor. Tires are matching on passenger and drivers side and are inflated to equal pressure. Before the issue with the front struts leaking the car always sat level.



When I scan the computer with VCDS I get the following error code from the Active Suspension Control Module:



Address 34: Level Control Labels: 4E0-910-553.clb

Part No SW: 4E0 910 553 H HW: 4E0 907 553 F

Component: LUFTFDR.-CDC H06 4480

Coding: 0015510

Shop #: WSC 22807 004 1048576

VCID: 285F08059B2370C46A-807C



1 Fault Found:

01772 - Signal from Level Control Pressure Sensor (G291)

008 - Implausible Signal - Intermittent

Freeze Frame:

Fault Status: 00101000

Fault Priority: 3

Fault Frequency: 4

Reset counter: 68

Mileage: 137485 km

Time Indication: 0

Date: 2020.12.05

Time: 12:57:47



Clearing the fault and driving for a while brings it back but it does not return immediately.



The RossTech Wiki says this about the error:

Possible Causes

• Wiring issue between G291 sensor and J197 Control Module
  
• Faulty G291 sensor
  
• Faulty J197 Control Module
  
• Air leak in system
  

Possible Solutions

• Inspect and repair wiring harness
  
• Inspect for leaks with soapy water
  

I've preemptively purchased two new rear struts and the passenger rear level sensor. Based upon what RossTech says I am not confident that installing them will make a difference. I've gone through the full design guide on the air suspension system and I'm not clear what could be causing this. I'd like some advice and perhaps other ideas for diagnostic that I could run myself before taking it back in for service. This is getting very expensive.



Thanks,

DU

Giovanni Giovino 6.0+6.0TT

Hello @DiagnosisUnknown ,
Have you checked the value of each level sensor reading to see that the leaning side is actually working, as I am just getting ready to fire up my B GT as my rebuild is nearing completion, I had just finished installing all new brake rotors and pads Thursday night and decided to put the relay and fuse back in to let the suspension do it's thing, well, it did nothing, and VCDS showed a short to ground on the left front, but only said the left rear had intermittent fault in circuit, I unplugged the left front and the short fault went away, so that tells me that the fault is in the left front sensor itself, but the left rear did nothing, so I went into VCDS suspension control module and then into measuring blocks and checked channels 004 and 005 while at the same time disengaging the level rod from the lower control arm on the left rear, my reading stayed the same, stuck at "128", (just to note that the right front and rear both showed fluctuation of readings when moving their rods, or just the body of the vehicle) so I swapped out the sensor from the parts vehicle pile of parts, I cleared the faults, and just as I plugged in the sensor and moved the lever a small amount, the system came to life.

So if I were you I would be checking for value changing of each sensor with movement.

I did not take pictures of the VCDS screen, so I grabbed these from the internet for ease of instruction.

Johnny

...

DiagnosisUnknown

Excellent information Giovanni and thanks for replying! I've never seen that interface so it's a first for me today. I just checked this and I think the sensors are all working. I scanned the vehicle in automatic mode and in lift mode and all of the sensors values changed while I watched them:

This is in Automatic mode

This is in Lift mode.

The Deviation in the rear from standard level certainly seems to correlate to the 1CM+ variance I am seeing between the right and left sides. So, it would seem that the car is aware that it is off level but isn't correcting for it. Now I am even more confused! Any more suggestions?

Thanks,
DU

Giovanni Giovino 6.0+6.0TT

You most likely need to check if any of the sensors mounting brackets got bent, or moved in any way, that would throw off the actual reading.

ltooz_a6_a8_q7

If it were me, I would swap the left and right before I replace anything. Who said there's no operator errors while replacing the rebuilt struts and they're totally the same?
Cheers,
Louis

DiagnosisUnknown

Louis, when you say swap the left and right, do you mean the struts or do you mean the sensors? I thought both of them were unique to a specific location on the vehicle. If we assume that the rebuilt right strut rides a little lower than the left one would the difference in the front induce the difference in the back of the car?

Thanks,
DU

ltooz_a6_a8_q7

Logically, we should understand why one is lower than the other. The air suspension heights are dependent upon the extension of the airbags. When one side is lower (shorter) assuming there's no leaks, means physically shorter, if the controller pumps air with the pressure to supposedly leveling the car and strut is physically lower then the only thing I can think of is the airbag doesn't raise to the height it should be. There are instances that people mistakenly installed 2 shock bushings by mistake and make one higher than the other. Now, if we consider both strut level sensors on one side are bad, which I doubt they are.
The G291 in the valve block, it would control both front or rear and not one side or the other.
Back to basic, both front and rear are independent due to the valve block. I've never had to use VCDS to fix mine and I never mess around with Audi control System, I trust their controller, when you messed with it and it may go into a state that the controller is not programmed and the system is a walking wounded which is unknown state.there's no reset to factory default. IMHO, the dealer calibration caused the problems and they don't know how to get back to default state. I doubt even if you replaced all 4 new struts, level sensors the car will be the same because a register(s) was over written with a value(s) that the controller doesn't understand. It may be the software problems now. That's the reason why if I can't work on my car, I won't own A8L.
Cheers,
Louis

Veikra

How's the ground where you took the above mesurements? Flat concrete?

DiagnosisUnknown

I measured it in two different locations. Both were flat. One concrete. One Asphalt. Both had the same result.

Veikra

Good. Next step is to validate if the basic heights in the computer are reflecting the situation. I think someone started messing with the calibration and something is not right. Go to calibration and look at the channels, you wont have to change anything just yet. Post us all 4 screens that show the current(old) values such as 410mm front 385 rear. We have to make sure it has the correct height to begin with else it could explain why its not trying to level.