W219 Rear Indicator issue

[Larkone]

Yesterday the car reported that the rear left indicator (led) had failed and it was using the backup light (reversing light). Took out the light unit out and there was some corrosion on all of the push connections on the circuit board - nothing major, but worth cleaning. Re-assembled and the indicator light worked perfectly until I started the car and it switched back to the backup bulb.

My thinking is that the circuit board for the indicators is failing and is fine when running off the battery but as soon as the car starts and the alternator is charging the voltage is higher and causes it fail again. The error code is 9066 - saying that either the light has failed or there is a break in the circuit, which is unlikely as it works with the engine off. Therefore a new back light unit or have I got it completely wrong and it is something else that could be causing this?

Any help gratefully received to this new CLS owner.

 

[Larkone]

Ok - Replaced the complete rear light unit and it all works perfectly now.

So if the rear/brake/indicator light fails on these led units you have to replace the whole thing. Very expensive bulb replacement. The units seem to be plastic welded together so no hope of getting to the circuit board, which must just be an led driver, and repairing them.