Dnasty

I get this solid illuminated block on the left side inner taillight when I turn my light knob as shown and pull out. I think this is supposed to be a parking light but why only one side is this normal? I’ve been trying to diagnose a non functioning right drl and wondering if this may be related.

crazy00c230k

It's the rear fog light, only supposed to be on one side.

Dnasty

Ah ok I thought maybe something was off because I was receiving a tail light code. Any idea what a single rear fog light is for? Doesn’t seem particularly useful.

crazy00c230k

Just a nice bright light to help make you more visible in the fog. I assume it's only one side so it isn't confused for/is easily differentiated from brake lights by people behind you.

Grant_J

On my '16 the light has a separate button next to the light knob to shut it off. Even with that button in though it only comes on when I set the headlight knob to On. In Auto mode the fog light stays off. Tested it one night while my wife was following me and she said the thing nearly blinded her. Yes she's dramatic... Anyway, I don't recommend leaving it on full time unless you want to see a lot of road rage in your future.

Barry Hanna

And what I just learned is that on an SL (perhaps other models) the right upper light only comes on in the event of a brake light failure and it then substitutes for the failed light. So, it just waits patiently and in the dark until it’s brother stop light fails and then steps in. Engineered like no other light in the world.

griza

I could be wrong but I had heard this rear "fog" light is only on the driver's side so high speed driver's on the autobahn can see the vehicle from a further distance and which lane you are in.