Yellow warning light triangle in the door mirrors, has stopped working.
Only colour is now red! Any ideas, please?

 

If something stops working as it was firstly you should consult your dealer.

Here is some info about MB BSA. Also I do not recall the triangle ever being orange, it has always been red in my experience.

 

Agree with suby. Head to the dealer, get a snack, get a loaner and save your wear and tear for a day or so.

No brainer.

 

Ya, on the older 212 it turned yellow when under I think it was 20 mph or so. My 213 has never turned yellow, just red when there is car next to me.

 

I’ve never seen yellow with mine either.

 

I must concur. The only color blind spot I've had is the red triangle. Your yellow might have been a glitch. According to the owners manual, the triangle should be red.

 

I’ve had my E450 cab in for service a couple times and both times I got a non E-class loaner. Has a C250 and a GLA something.

First... wow are both cars seriously underpowered compared to my E450 but they also had the yellow triangle thing. It stays on to warn you it’s not really looking in the blind spot under 20 mph. Why?!? That makes no sense. And I really found the constant warning in the mirrors distracting

 

As it pertains to your vehicle Blind Spot Assist yellow triangle is a readiness indicator when the system becomes active (about 20 mph) then disappears. If the system detects another vehicle this is indicated in the first stage by a red hazard warning triangle lighting up in the respective outside mirror. Have your dealer check it.

 

This is not true on the W213. There is no yellow triangle under any circumstances according to the manual...only red. Page 209.

 

Granted however, may be unmentioned variables involved since OP is convinced he had readiness triangle and now does not - 212, market, etc. this is why I emphasized "your vehicle". Should be clear if and when OP replies.

 

Know that on the previous MBs I had it was yellow when you started the car and also below I think 10-15 mph as you drove, it stayed on continuously and then it went away unless it turned red because it detected something. Have not really noticed on my 2019 as either I'm used to it or have not noticed that the Yellow is no longer there. Not sure why they'd take it away as it was a way that you knew the system on startup was actually working. I know it's pain but go to the owners manual and see what it says. Or as other have said, if in warranty drop by the dealer.

 

On startup red triangles are shown for a few seconds on my 2018 E300.

 

On my 212, I would notice the yellow triangle while driving down my street at low speeds, then it would go away. On my 238 I only see a red triangle as a warning.

 

Maybe it was senior moment and he was remembering his 212 and thinking the 213 was the same.

 

As usual, the OP doesn't state model or year car....just W213. Methinks he has a W212 and has posted in the wrong forum as 2012 Merc has pointed out. Until he reposts, there's no use of doing anymore second guessing.

 

Thanks for reiterating

 

From the Operator's Manual for the 2016 E-Class Sedan (p. 179):
From the Operator's Manual for the 2019 E-Class Sedan (p. 213):

 

How is it that there are multiple comments and potential suggestions for the OP, but we have not had any response?