Mendota

Hi,
I've seen this error twice since I bought the 2011 GL450 a couple of months ago. For both times, I saw the the error as attached saying "Trailer tail lamp right" as if the vehicle trying to light the trailer tail lamp but couldn't. Actually there was no trailer attached, and they both came up when I turned on the engine a couple of hours after driving in heavy rain.
For the first time, it went away the next day without any change, and a local shop couldn't find any error in reading the code. I'm afraid that there is a leaky spot where water got in causing the confusion, but I couldn't find where that might be.
Anyone can shed some light? Thanks a lot.

EWT

Do you have a trailer hitch? If so, I'd check the terminal (with spring loaded door over it) to the left of the receiver that you plug the trailer electrical connector into. Look for moisture, or something that might be making an electrical connection between the terminals.

alx

this and common. your hitch connector is getting moisture inside.

clean up the area with compressed air, spray some dielectric grease in there and make sure the connector cover seals the connector area.

CBR Dude

This is correct! Check the cap and make sure it's all clean under the cap. The lane monitoring will deactivate when the system detects a trailer plugged in. In your case the system sees the none working trailer lamp and then deactivates the lane monitoring system. Mercedes is very over engineered on this. If you have or will plug in a trailer with LED lights this is very common.

DennisG01

And about the LED trailer lights... You will get all kinds of weird things happening if the vehicle expects to see incandescent lights and your trailer has LED's (and vice versa). At least for my 2008, I would have to have the computer reprogrammed every time I switch from incandescent to LED and back. So I have the computer programmed for regular lights and when I trailer something with LED's, I have an adapter that has resistors built-in to trick the computer into thinking the trailer's lights are not LED. I plug the adapter into the vehicle side connector, first... then the trailer plug into the adapter.

I must say that it seems silly that I have to go to a dealer to get this programmed every time. This SHOULD be something that I can select in the information center in the dash (between the gauges).