[johnny_quattro]

My front sensor was physically broken around 2 years ago, as the plastic arm had a 'stress fracture, shall we say. This was replaced with an item from the forum sponsors and a reset performed by Adrian E.

Recently, the warning light came on my dash for the headlight levelling sensor (HLS) and quick check on my OBDEleven app/dongle showed that the rear HLS was not working. Ordered a replacement from the forum sponsors and fitted it yesterday. Fault was cleared on the car's computer but the app was complaining about resetting the headlights.

Further checking via the OBDEleven app showed the front sensor at 2.4V and the rear sensor at 0.5V. Mmmmm. I had no doubt that the replacement part should have been working correctly. Pushing vigorously on the car's rear suspension showed the voltage value changing in real time but only by 0.1 or 0.2V.

Took the car down to Adrian E to perform the headlight reset procedure on his VAG COM setup. A quick check under his S8 quickly revealed that the sensor arm orientation on my car was wrong. Looking from the back of the car to the front, the straight arm of the sensor was at 4 o'clock, which is WRONG and accounted for the incorrect voltage reading of 0.5V instead of 2.4/2.5V. We took the wheel off and with the judicious use of a trusty 10mm spanner, it was corrected. The rear HLS on mine now points towards the outside of the car almost horizontal, at 9 o'clock.

See attached photos showing my rear headlight levelling sensor (and how it was installed wrongly by me) prior to the change. To summarise, when looking from the rear of the car to the front, the rear HLS plastic straight arm (marked A in the photos) should be at 9 o'clock and not 4 o'clock.