Welcome to XT660.com Alastair.

I don't think any of the stored codes you had were/are necessarily anything to do with your current problem? Although 21 is the coolant temperature sensor. If it was still malfunctioning though the bike probably wouldn't run right (as the signal to the ECU is fixed at 80C) and the engine trouble light would be on.

Not sure why your fuel injection system voltage is 0? The bike wouldn't run if that was the case and if below 12V and running the engine trouble light would be on?

If you know the fan is good, and the engine trouble light isn't showing (at the moment), then you can rule out the fan, the coolant temperature sensor and any fault with the ECU (as the last two would throw up the engine trouble light).

It is perhaps most likely something to do with the wiring, the fan's fuse or it's relay, as all these things will cause the fan not to work and overheating, but give no engine trouble light or error code - just the temperature warning light.

Have a look at the following:

1) Check the fan's fuse
2) Check the connections on the fan relay are good
3) Check all the wiring in the fan circuit for abrasion/corrosion
4) Run the D51 test (which checks the fan relay) and listen to see if the relay clicks

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