w204 rear ABS sensor

[sceh]

I have the ABS/ESP lights on the dash so I need to check the rear ABS sensors since I suspect one might be duff. I has the workshop manual but it has no mention of these sensors!
Are they pretty self evident when I take the wheel off? I am intending to check the resistance as a first step.
As an aside, I have the electronic format WIS. If anyone has it can you tell me where the rear ABS is mentioned??

thanks