Fortwo brakes stuck on.

[Bobby 2000]

Thanks for clearing that up.
It would certainly make sense, if the if computer is telling it to hold for some reason but then not releasing them.
I checked the fluid this morning, had to make myself a special tool to unscrew the cap because it was so tight and I couldn't get enough grip. I did wonder if it was a bit low, but couldn't see a level mark, so left it as it was.
I will try to have a look underneath at some point.
I appreciate your help and I will let you know how things go.
Bob.

[Thrumbleux]

To access the master cylinder/servo you will need to raise the front of the car as high as possible, lower the (hinged) front part of the undertray and send a small child in to inspect. It is a PITA and god help you if you have to access the top of the ABS unit - then the rear tray needs to be lowered also.

HSA doesn't function if the handbrake is used. Try raising the handbrake lever just enough to illuminate the light on the dash and you should notice an absence of HSA. If that handbrake setting isn't pulling the handbrake drum on at the drums, maybe you can drive like that to see if HSA isn't the problem but as your problem is intermittant, not necessarily conclusive.
Can't remember the circumstances that invoke HSA. Just sitting hand brake off with foot on brake I think. Cant remember if being in neutral or a gear makes any difference. Handbook should have more info. Definitely it should release about 0.7s after removing foot from brake.
If the HSA is malfunctioning - I'd expect error codes and possibly/probably lights on the dash.

[mottofreee]

Does HSA act on any inclination? YAW what does he have to say?
A YAW recalibration can only solve the problem or replace the ABS unit is the solution?

[Thrumbleux]

HSA functions as foot brake is released and car is in gear. Irrespective of inclination. It must be speed or gear sensitive though or releasing the brake in normal driving would result in a delay before the brakes were released.