Hi again. I think I've worked this out. I reckon my mechanic has been wasting my time. He definitely told me "gearbox temperature sensor". I wrote it down in front of him but I suspect it actually read or meant engine temperature sensor, which is why replacing it is "lol". Thanks to anyone who was thinking of helping. I will get back to mechanic clarify the diagnostic readout probably replace engine temp. sensor anyway & go from there.