NSX2NV

Hotsauce55

sjc246

There are a few different things that can turn on the red brake warning. The obvious (or at least, most feared) answer is the SBC timeout (which requires replacing the entire unit), however, before you worry too much about that, you need to check codes with a high-level scan tool (or, ideally, the Mercedes SDS aka "Star"). The red warning can also be turned on because of a failed pressure accumulator, which isn't cheap, but isn't nearly as bad as an entire SBC unit, or it could just be the brake light switch, which is cheap and very easy to replace. If the unit is disconnected while the battery is still connected, it can sometimes turn on the warning light afterwards, but that should go away after a few key cycles if everything is good.

As far as I recall, there are no control units under the flat part of the carpet (which would likely get damaged by a small amount of water). There are a few in the front of the right front footwell, but they're high enough up that it's unlikely that they would get wet unless you had several inches of water in the car. Regardless, fix that leak!

actech

i got that when my main battery was about to die

tw2

Check battery condition (both of them and not just voltage- a proper tester), then check charging voltage and codes for BCM. It could be an electrical issue if multiple things are not working correctly rather than just a braking issue.

lseguy

agreed with above. And a weak/dying battery (and or charging system) thats not consistently putting out proper voltage can result in a number of weird errors/error messages.

Yuille36

Also check the pad thickness of your brakes, if they worn down, it could be the brake pad wear sensors telling you that it's time to replaced them.
As this could be the reason also.

sjc246

A pad wear warning should be white, not red.

Yuille36

Thank you, I didn't know that fact.