Thanks everyone, I hope it is useful. A correction to Note [5], I can if fact get codes out with the key in position II, I think it was so fiddly when I tried this with paper clips I couldn't get it to work. (I would fix this but I don't seem to be able to edit my own post!) However, with the engine running codes only seem to be available around tick-over, I guess the micro computers are too busy when the engine is at revs. Also I can confirm the instructions for deleting codes provided by Jod T5 work fine with a 940.