850 Temperature Readout- Help!

[u05je7]

Ok, N Reg 850 2.5 20V. It's been sat for a day so the engine is cold and I've just attempted to start it. The temperature gauge immediately shoots up into the red where it stays. The fan kicks in instantly. Checked all the usual things, coolant is ok, oil, hoses etc. Wiring to the coolant sensor also looks ok. I don't have a diagnostics port so can't get a readout. Any ideas?

Thanks in advance.

[morgrp]

You played with the ECU or battery at all?

[u05je7]

Nope, nothing like that.

[Callyuk]

start at the eaiest option check the temp sensor itself could well have failed