A6 Allroad 2008 All Suspension Dropped Compressor Not Running

[owenappleton]

Hi

I wonder if anyone can help with this issue rendering my A6 Allroad undriveable? Last week I was driving to work and the yellow air suspension light came on suddenly - suspension had been woring fine until then, if perhaps a little slow. It had sat perfectly level all round and never dropped overnight or anything like that. Within a couple of minutes all the suspension had dropped completely to the ground. I drove the couple of miles home, very slowly, and took out the compressor to check it over. It wasn't running when the car was switched on but, after removal and connection up to a power supply, the motor ran fine. I've decided to replace with a new one anyway which I have fitted tonight.

No joy - the new compressor doesn't run and, when I tested the power supply from the car with a multimeter, there was no voltage.

I thought that maybe the 40A fuse or relay was at fault and have searched out several that I thought may control the compressor. There seem to be a lot of different possible locations - the relay (643) in the plenum chamber under the bonnet (driver's side, RHD car) and fuse there seem fine, as do the ones in the driver's footwell (again 643). I swappped each of these over in turn to see if that made a difference. There are another couple of relays with a 370 number that I haven't swapped over to test yet. I'm not really sure whether any of these are the right one really - all advice welcome!

Any thoughts please? It's a 2008 C6 model, 3.0TDI that has been ultra reliable up till now.

Thanks, Owen

[Crasher]

Any fault codes?

[owenappleton]

Haven’t checked yet as don’t have a Windows laptop for the software - nothing showing up on a basic reader. Will hopefully be able to check by the weekend. Will the compressor fail to operate if there are fault codes that haven’t been cleared?

[Crasher]

It will only shut off if it overheats.

[owenappleton]

Ok, thanks. I disconnected the new compressor and connected it directly to 12v to check it’s ok, and it runs fine. No lift to the suspension though, and still doesn’t run when plugged in to the car.

[Crasher]

I need to study the wiring diagram but my offline elsa crashed and I am waiting for a new version; you need to do a fault code read.

[owenappleton]

Right, progress I think. The first scan showed up these codes:
5 Faults Found:

00775 - Level Control System Sensor; Rear Right (G77)
008 - Implausible Signal - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10101000
Fault Priority: 3
Fault Frequency: 1
Reset counter: 188
Mileage: 253030 km
Time Indication: 0
Date: 2022.03.18
Time: 08:15:27

01768 - Sensor for Vehicle Leveling; Right; Supply Voltage
002 - Lower Limit Exceeded - MIL ON
Freeze Frame:
Fault Status: 11100010
Fault Priority: 3
Fault Frequency: 4
Reset counter: 190
Mileage: 253030 km
Time Indication: 0
Date: 2022.03.18
Time: 08:15:44

02646 - Plausibility of Level Control System
008 - Implausible Signal - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 230
Mileage: 253032 km
Time Indication: 0
Date: 2022.03.18
Time: 14:46:59

01397 - Venting Solenoid for Level Control (N111)
011 - Open Circuit - Intermittent
Freeze Frame:
Fault Status: 00101011
Fault Priority: 2
Fault Frequency: 1
Reset counter: 230
Mileage: 253039 km
Time Indication: 0
Date: 2022.03.18
Time: 17:53:59

01399 - Relay for Level-Control Compressor (J403)
011 - Open Circuit - Intermittent
Freeze Frame:
Fault Status: 00101011
Fault Priority: 2
Fault Frequency: 3
Reset counter: 230
Time Indication: 0

After clearing all these, the compressor jumped into life and the car started to lift. Height settings now on again instead of greyed out and the car stays up. The yellow warning light is still on, however, and a new scan brings up this fault:

1 Fault Found:

01768 - Sensor for Vehicle Leveling; Right; Supply Voltage
002 - Lower Limit Exceeded - MIL ON
Freeze Frame:
Fault Status: 11100010
Fault Priority: 3
Fault Frequency: 1
Reset counter: 190
Mileage: 253039 km
Time Indication: 0
Date: 2022.03.25
Time: 18:24:45

So, do you think that could have been the problem all along? And hopefully a simple fix of changing that sensor? If I can find where it is, that is! Any thoughts? It seems strange that the whole car dropped suddenly at al corners when there were no perceivable leaks from anywhere before that point.