thanks for your replies I tried to scope the front sensor but as it was broadband I couldn't make any sense of it. in live data it refers to it as equivalence sensor and the output is the same as the required and as I said this is the same as the saved live data taken a few months ago. the fuel trims do reduce a bit at higher revs does this mean something? after using a different scanner I got a better description of the fault it said sensor one slow response. the fault cleared but came back after 14 miles. if it was the normal oxygen sensor I would have no problem confirming if it was slow but how do you check this equivalence sensor? by the way it costs £300 from nissan