This is what my C110 said. One of the pressure circuits was reading a high positive bar with the brake pedal depressed (I also got a reading at + 20 bar with pedal depressed at one point).
I decided to replace both sensors today for piece of mind. Both are located on master cylinder, no. 2 is the one nearest the bulkhead, no. 1 is the front most (with the spanner on it in pic).
They are both 27mm. You can just get a spanner on to undo, tho I've heard some undo the brake lines close to the sensors for access. If you want to use a socket it'll need to be deep.
Release the electrical clips (push the tabs and slide off), unscrew and remove each sensor in turn, trying to minimise fluid loss by screwing the replacement on straight away.
Once the new sensors are in bleed the system. If your car is RHD do it in this order (basically furthest bleed nipple from the master cylinder to the nearest).
Rear passenger
Rear driver
Front passenger
Front driver
The bleed nipples are on the top of the calliper and a one man bleed kit works fine. The nipples are 9mm and don't forget a squirt of WD40 before trying to open them.
My C110 gave good readings after the job
With each circuit within 1.5 bar of the other and the traction control lights now off permanently.

for JamesUK