Dusk and rain sensor problem solved

Isola
Posts: 26
Joined: 15 Aug 2011, 12:28

Dusk and rain sensor problem solved

Unread post by Isola »

For a long time I've experienced problems with the dusk and rain sensor. I've got fault indications from it ("Avaria sensore crepuscolare") associated with on/off flicker of the instrument cluster backlights and sporadic operation of the automatic wipers. Finally the rear ceiling light started to blink, alternating the left and right reading lights, and was sometimes lit up after locking the doors.

It turned out that the GPS antenna leaks drops of water onto the rear ceiling light, leading to electrolysis on the PCB which is not coated with protective lacquer. The fix is easy: remove the rear ceiling light by prying on the front edge, then clean the circuit board with an electro cleaner. This fix has kept all those symptoms away for several weeks now.

The rear ceiling light is a "dumb" slave unit connected to the front ceiling light (the NIM), and probably the constant leakage currents drive the microcontroller on the NIM mad by keeping it busy all the time. I haven't verified this from the wiring diagrams but to me it makes sense. At least both the rear ceiling light and the dusk and rain sensor have now worked flawlessly.
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