Mine went haywire about 5 years ago on my 2010 4/4 sigma. I got a new sender/cylinder from Williams and fitted it - Solved the problem. But try cleaning the contacts first and give it a good blast with high revs for a couple of miles to see if anything has got stuck. When changing beware that on mine there is a brass step-down joint which is quite susceptible to damage - may be an idea to save time to order one of these at the same time. Luckily - in my case- my local garage rethreaded a step-down they had in -but not many places could be arsed to do that.
