D2 Td5 electric fan always on

As already mentioned, the fan will be turned on by the ECM when stationary for a few different reasons.

1. If the AC is on and ambient temperature is over 28.

2. If engine coolant temperature is over 110°c.

3. If a bad overheat has occured and the fault not cleared (I can't remember the number, but it's hot, you would need a new head after).

And

4. Yes, I think a failed temp sensor might put it on as well.

I'd be checking the relay as suggested, then go from there.

The ATC ECU could also be faulty I guess.

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Originally Posted by Campaspe Man

Thanks Dave. In relation to the stuck relay idea, would the fact that I can force it off using the Hawk Eye suggest this isn't the cause? And if not, can a stuck relay be unstuck?

Cheers, Myles

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Im pretty sure that your on the money if the hawk eye is shutting it off that its not a stuck relay but Id want to sit down and relook at the trace for the main feed to the fan relay just in case its using a second control relay. Some vehicles have multiple control paths that aren't immediatly apparant (one relay feeding another, one from say AC, one from an overheat control) off the top of my head Im cant say for certain that the TD5 electro mechanical control doesnt do the same thing.

Stuck relays can be unstuck but its usually only a temporary fix, relays are cheap enough to just replace if they are being an issue and usually you can swap them one for another and see if the fault follows the relay by causing a problem in another system.