W177 Headlights Randomly Turn On Low Beam

[Alinut]

I had a problem with the Multibeam headlights on my W177, the low beams would randomly turn on when parking. In all cases, only one headlight was turned on. The problem usually went away on its own since I couldn't do anything to turn off the headlight. I changed the ECU for both headlights at MB workshop, but the problem remains. Also after replacing the ECU, the LEDs are not aligned, and the light pattern for both low and high beam looks bad, with noticeable dark spots.

 

[feodorbk]

Are there any other errors on the car? Have you diagnosed them with a scanner?

 

[Alinut]

After replacing the ECUs, no errors were recorded in this regard. There were some stored errors, but they seemed to be caused by low battery voltage, some exhaust sensor malfunctioning, and other similar errors.

 

[feodorbk]

I think that it is worth checking the radar sensor and the wiring connecting the front bumper.

 

[Alinut]

I removed the front bumper trying to get to the LED CODE marks on the headlights, they are not accessible without removing the headlights themselves. The wiring to the front bumper looked fine, connectors too. The connectors for the headlights also looked fine, nothing out of the ordinary. I did not check the radar sensor as it was working fine. It is worth mentioning that I tried to do the SCN coding for the left headlight using the Xentry and it gave me a message saying it could not do the coding. I do not know if this is due to the Xentry being offline or something else entirely.

 

[feodorbk]

Trying to do online coding is not scary without the Internet in Xentry.
I asked about the radar and connectors, because there were cars with a sunken sensor and a broken can. The glowing headlights, it seems to me, are associated with a lack of communication. My headlights burned like that on a W205 with shorted bumper connection wires going to the radar. And if I were you, I would put the factory headlight units back in place. Replacing them did not help and you need to deal with the problem, and not think about units that do not match the coding.

 

[Alinut]

Thank you very much for your help! I can't return the ECUs as they were replaced under warranty. I asked the dealer rep if he could return them to me but he said they were sent away for analysis. Is it possible that the CAN communication can only be faulty sometimes? I will double check everything and try to find out what error the car was giving when the dealer diagnosed it that made them replace the ECU.

 

[feodorbk]

A CAN connection failure can be caused by poor contact between the wires and connectors. I often see the problem manifest itself in damp weather, such as after rain. I would like to get an initial error code or, even better, a short test for the whole car immediately after the fault manifests itself.