Yellow light on - please help
 

In the 2 years I’ve had it my Allroad suspension has behaved impeccably until the other day when the yellow level indicator came on and wont go off.
The suspension seems to working ok and will go to each level in the normal way and all corners stay equal but still the light stays on. Another symptom is that the ESP button doesn’t seem to be working.
I took the car to a diagnostics guy and he came up with “ 00774 Left rear level control sensor -G76 “
He tried resetting the fault but it came back immediately.
I have examined the sensor, wiring and plug which look physically ok . There is 5v across purple/red and purple/black (pins 1 and 5) with ignition on. The other 2 pins show a fairly high resistance to ground. My question is do I assume that the sensor is to blame and if so why does it seem to be still doing its job? I haven’t got VAG.COM yet but it’s on order, should I wait and do some more investigating before buying another sensor and what test can I do to be sure?

Provided the terminals aren't corroded off at the sensor (common in Wisconsin, lol) I would suspect the sensor. You need to look at the sensor signals on a scanner to see what they're "reading". The car may stay level because there's a sensor on the other side that the suspension uses in default. I mean, it won't pump only one spring up and not the other.

With a missing level sensor input, the stability control will be disabled since it also uses the level sensor inputs and with one missing or implausible it deactivates basically for safety reasons.

Like I said though, look at all 4 sensor parameters on a scanner. Compare the left to the right (which is probably correct). They should be the same or darn close to the same.

Yeah I know, dumb question but,,,,,,,,,,,,the sensor link is connected to both the sensor and the lower link, right? Sorry, had to ask.

Thanks for the advice
 

Hi Aspen79
I have checked the sensor plug and mechanics and all looks well (I am an engineer by trade) But there's been a development since then. We took the car on a 80 mile trip for a Xmas holiday during which the light stayed on solid all the way but all was well otherwise. The car was left standing for 4 days and when restarted for the trip home the light had gone off ! Also the ESP button now puts the symbol on as it should. A couple of short trips have been done since and all seems well but I'm still nervous of it coming back.
I have bought one of the cheap OBD 11 interfaces along with VAG software free edition which enabled me to view and cancel two stored messages -----
0774 - "left rear level control sensor- malfunction in circuit"
and
01771 - "Headlamp range control module - J431 - please read DTC"

If the light does come back then I will take your advice and investigate further- when you say "scan the signals" is this something I can do with VAG.COM ? Perhaps I will need a certified copy as the free one is rather limited?
Incidentally I have been reading something in a VAG. COM manual that suggests some fault codes are programmed to remain present until a certain number of start/test cycles have been completed. I wonder if that was the case here?

It is possible you had just enough of a high resistance in the connection that unplugging it may have cleaned it off. The sensors use millivolts so it doesn't take much corrosion (that's basically invisible) to skew the readings. Happens on airbag systems all the time. All it takes is 0.1 ohms over or under the specified resistance and the airbag light will come on.

Yes, after a certain number of drive cycles, if the fault isn't detected again the warning lights will go off.

By "signal" I mean looking at the parameter reading. Hard to explain what I'm trying to say here! Basically, you need a scanner that can read live data from modules and then you bring up each sensor i.d. and see what voltage they're showing. One of those things I can do but when I try to put it into words..........Kind of like showing someone how to tie their shoes. I've never actually seen a VAG.COM but assume it's similar to the factory issued Audi scanners (?)
The headlamp range is related to the suspension and level sensor. The headlamps use the signals from the l.r. and l.f. sensors to determine the headlamp aim and adjust it accordingly. Even models without air suspension (and with HID lights) have a sensor on the l.f and l.r. Most of this is from memory, I haven't been an Audi tech for 1 1/2 years now (went indy).

Hopefully you got lucky and it's all good now.