Cannot Retract Brake Caliper Piston

[EViS]

It's time to replace all the discs and pads on my 2013 Mercedes A250 (W176). I've started at off-side rear and all was going well until it came to retract the brake caliper piston back in to fit the new pads. It just won't squeeze in, I've even tried loosening the bleed valve and unscrewing the brake reservoir cap. I tried so hard that my brake piston wind-back tool snapped *sigh*.

In addition, is the black plastic box at the back of the caliper the electric parking brake actuator? Haven't come across this before, probably because I tend to work on slightly older/less sophisticated cars.

Edited by EViS on Sunday 18th August 15:45

[EViS]

Thanks all . I feel like such a numpty! First car I've ever worked on with an electric brake and obviously didn't appreciate fully how they function! A quick search and I found how to get into the service menu to wind the electric brake back, smooth sailing from there!

Here's hoping I didn't damage anything with the excessive force I put into the wind-back tool . Took the car for a quick drive and engaged the parking brake a couple of times, all seems well atm.