Hi!

My light/rain sensor is not working at all. No ''regular'' fault codes stored, 12V to the sensor, but when i hook it up to Auto-com and read real time data it says following

''Rain sensor internal fault''
''Light sensor internal fault''
''Rain/light sensor adoption error''
''Rain/light sensor communication failure''
''Sensor rain/light-sensing: function limited by undervoltage''
''Sensor rain/light-sensing: function limited by overvoltage''

Ch/lh does not work either, because the sensor think its daylight all the time.

Any ideas? The sensor that's malfunctioning? Or something with the central electronic module?

 

Since 2015, this thread has received over 10,000 views without a response.. . For those continuing to arrive here from search engine links, it seems worthwhile to post possible resolutions for when the Light/Rain sensor is not working.

First off, your vehicle is likely showing the following error light:

To diagnose, scan for fault codes and/or read channel 20 & 21 in module 9. Rossteck VCDS linked below for reference.
http://wiki.ross-tech.com/wiki/index..._%288EC/8ED%29

Other members have reported that unplugging the connector to the mirror and plugging it back in has resolved the issue.
Alternatively, it's been reported that after unplugging the negative terminal on the battery for several hours, the issue was resolved once the battery is connected again. See the thread linked below for reference.
https://www.audiworld.com/forums/a4-...senor-3067719/

If you determine that your rain sensor is broken, then you may want to consider replacing the entire mirror assembly, or, purchase a 8K0955559 sensor to replace the one in your car's rear view mirror. Examples of sensors for sale as of today, 14Jan2025, are linked below.

New Rain & Daytime running light Sensor - 8K0955559 - $335 USD as of 14Jan2025
https://www.ecstuning.com/b-genuine-...or/8k0955559d/
Used Rain & Daytime running light Sensor - 8K0955559 - $60 USD as of 14Jan2025
https://wolfautoparts.com/rain-light...9-ps18200.html

You can familiarize yourself with the replacement procedure by watching the videos linked below.

How to remove you rearview mirror (~30sec).

How to replace the sensor (~13min).


Best,
Yapzehemnem