I just bought a 2007 Polaris Trail Boss 330 and noticed a problem with the oil cooler fan. The fan is running constantly, even with the key out.

I opened the hood, and if I disconnect the power to the fan (Brown & Red/Blk Stripe wires) obviously it turns off. I then disconnected what appears to be the thermistor, (Yellow & Yellow/Blk Stripe wires), and re-connected the power and it still turns on.


What should I check from here?


Thank you for all the great information and advice in these forums.

 

I should have noted:

The Oil Temp Light is not illuminated.

The thermistor is reading 64.2k when checked in the hot garage.

 

Maybe you've found your problem! When a thermistor shorts out the fan can run constantly. (Part #4010934.) BUT according to the manual I have though, at 77 degrees, resistance on thermistor should be 100 k ohms + or - 15% (fan should be off) At 260 degrees + or - 15% the thermistor resistance should be 2.5 k ohms (fan turns on). If this is within range on the thermistor,then the control module(ecm) could be faulty as it controls the fan(from input from the thermistor) and also controls charging back to the battery.Then manual says to replace the ecm module.You can take a heat gun if you have one or boiling water to check out the thermistor resistance as close as you can get. OPT

 

Thanks OPT for the info. Tomorrow morning when it is closer to 80 degrees in the garage, (got to love the desert!), I will re-test the thermistor, then I will hit it with my heat gun and see what the meter says.

I am assuming that if I jump the wires in the connector to the thermistor the oil temp lamp should come on, don't know if that would help diagnose the ECM vs Thermistor problem. If there is a way to test the temp warning light I would like to know so I can at least make sure it is working!

I wish I had something laying around to give the ECM a fake 100k resistance reading to see if the fan shuts off. Would disconnecting the battery for a while possibly "reset" the ECM?

Worst case scenario I guess I could just put a 12V switch in the fan power line until I replace the offending part.

 

Ok, so I got up early this morning and re-checked the thermistor:

70 degrees outside, probably 80 in the garage, the reading came back at 85k.
I hit it with my heat gun and was able to brought the resistance down to just 2k in less than a minute before I stopped. A couple seconds after stopping the reading began to climb back up at a slow steady pace.
Looks like the thermistor is working?

I plugged the fan power back in, still running at both 5-10k & 70-80k.

I unplugged the big connection to the ECM, fan stops.

I tested the connectivity from the yellow/black wires from the ECM connector to the Thermistor connector and all looks well.

I am going to assume the ECM is freaking out, unless there is a fan relay somewhere that is stuck open?

Should it be the ECM I will probably just install a fan override switch, to avoid the cost of a new ECM, unless this would pose other problems.

 

Remember the ecm controls charging also and possibly could have charging problems later on or even worse problems if it over heats. Bad system I know. OPT

 

That is a bad system. Can't afford spending $200 on an ECM right now, maybe in the future. Charging seems to be OK as of right now.

Is there anyway to test the overheat warning system so I can be sure the light will come on to warn me of any issues?

 

It's all tied in with the thermistor and ecm module. If it's any conciliation, it takes quite a bit of heat to turn an oil cooled 325 or 330 fan on (260 degrees) A lot of owners have never had em kick on. OPT

 

Ok, good info. I ride in the High Desert, and when it is 100 plus degrees outside things can get hot quick if you are not moving fast enough.

I will probably throw a temporary 12V switch in between the connectors on the fan power line, at least until a replace the ECM. That way is I am cruising very slow, towing, or stopped and idling I will know the fan is running.

Thanks for your help OPT!

 

Hello,

Excuse me for my english, I 'm French and not speak english well.

My father have a Polaris Trail Boss 330 and he had a problem with his ECM and I had changed this controleur.
It's OK for the battery.


But I dont view the fan run.

I tested with a variable resitor and the fan run at 2.4 K ohm it's good apparently.

At what degré the fan has run. I see in this post, 260 degrees it's ok ?. It's degrees fahrenheit ? aproximately 127° Celcius. It's not too high ?

if it's OK, I test the Temperature sensor with a pan with oil heater I

Thank for your help