Thanks, It was tricky because the faulty earth point red herring, masked the real issue. I don't blame the Mobilo guy, as he was really trying to save me a shed load of money. His thoughts were also logical, namely suddenly all four sensors give problems and the “central” controllers earth looks dodgy. If only it hadnt been frozen on, one twist of a spanner and some emery paper could have ruled that out. And then I would have realised this required real work, and would have put it into an Indy and saved myself £200. The fact it was intermittant was the real issue. I learnt a lot, but at a price. One of the key things is apparrently my controller compares each sensor to the normal value; BUT ALSO compares its values to the other 3!