My fan doesnt work - update
 

my fan seems to have packed up, it usually only comes on in heavy traffic but as I have been to IOM & Donnington recently i have had to be careful.

What should I check for first

Because ST fairings are such a bastid to get off, a lot of people put off the need for a good fairings off inspection, and because all the temperature sensors and connectors live under the fairing, they get all furry and corroded. I would check the fuse first, then work my way through all the connectors etc

Check the temp sensors, especially for bad joints as Jools just said.
It might also be the thermostat.

Oh, another thought. My bike was getting hot last year (saw over 100 a few times, which is unusual). It turned out to be the oil cooler was blocked for a fair percentage of its area. A new cooler (not cheap !) has fixed it.

It only takes me about 20 minutes to strip all the fairing now - a decent long reach allen key and 8mm 1/4" drive socket (for the mirrors) is the answer.

My latest bit needing attention is the oil pressure switch - it is now an oil pressure relief valve, spraying oil all over the place at higher revs :rolleyes:
At least that can be done by removing just the lower panel...

what temperature should it kick in/out at ?

Based on my own 2003 ST4s, the temperature readout is driven from the front cylinder temp sensor, but the actual fan is driven from the ECU and this is fed from the rear. They are identical so you can swap them but if the bike starts OK from cold I doubt it's the sensor or else it would run very rough.

Check fuse of course but it could be the relay. All 4 relays on my ST4s are the same. Change the main beam relay with the fan one to check. All of this after checking the fan connections of course.

Fan cuts in at 101C (lights off). Yes the load of the lights affects the readout.

Hope this helps.


Norm.

Usual culprit for this is the relay - under the seat. Easy to get at, easy to check and replacement is only a few quid even from a main dealer.

By the way - the fan comes on around 220 farenheit if that's what the readout is in.

i had this problem, tried every thing never did get to the bottom of it.
checked the whole lot wiring, relay and sensors in the end i gave up and ran a new feed to the fan with a switch that i manually turn on and off.
i suspect in my case it was the ecu?

what Norman says...what I did with mine when it had the same problem to track down sensor, connection or relay issue

As mentioned different STs have different systems, if its a ST3 with a 5.9M ECU it will be controlled by a Negative Temperature Coefecient (NTC) sensor that once its resistance reaches a given value the ECU turns on the fan,
For an ST2 with a 1.6M ECU the Fan is probably controlled by a themostatic switch.
Removing the 2-pin connector from the switch and shorting out the two connector pins with the ignition ON should make the fan come on, if it doesn't then either the fan is faulty or a relay or fuse has gone.

My bike is an 04 ST4

How can identify the location of the relay and fuse that could be preventing the fan working.