Plus, inoperative collision prevention assistance

[Videoman]

E350d Coupe C207 from 2016.
Multiple instances of the warning "Collision prevention assist plus inoperative" have occurred; after scanning the vehicle with iCarsoft, the error code B21DE71 was returned. Due to a clogged actuator and a faulty relay, the Additional Battery is not functioning properly. After I reset it, it keeps popping back up at random.
I will verify it, but the primary battery seems to be in fine shape. The auxiliary battery, on the other hand, was replaced with a real one around three years ago. I saw the notice "Auxiliary battery malfunction" the last time the backup battery stopped working.

Using Google and the extra battery relay, we were able to locate the component number A0009822023. I need to know whether the auxiliary battery is okay, where to find the relay, and if they are a direct swap.
Does the A0009822023 relay work with all Mercedes models? I've seen ads for ones that seem to be model-specific.
Is anybody else familiar with this issue? Much obliged.

[Cincoon]

Hi there,

It should be easy for you to replace the relay, which is located in the fuse box.

[Starat]

When this happens on my W205, it's typically because of the radar sensor or the wiring around it in the grill.

[Anabroo]

Verify its continued presence.....

[Mezuzzi]

^^
They often "go walkabout" (often in the middle of the night)

[Mezuzzi]

😁😁😁