Ok got the bike fitted new tyres lowering links and new Cush drive rubbers rides like a dream. But there's always a but......
The cooling fan is pulsing on and off any idea's.

cheers swampy

Hi Swampy,

I haven't experienced this, but have looked at totally non-functional fans. A good place to start is the coolant temperature sensor. Section 6-4 and other sections of the service manual talk about it. They state it is quite a fragile flower!


Temperature sensors themselves are components which give decreacing resistance as measured across their terminals as temperature goes up. So if you have a decent multimeter you can test this at different coolant temperatures..

A guide to this for cars is here for instance,
http://www.howstuffinmycarworks.com/...mp_sensor.html

The temperature sensor should give out a resistance of 2.28 - 2.63 kohms at 20 deg C and this drops to 0.138 - 0.145 kohms at 110 deg C, so Yamaha say anyway..

If you were to remove the plug from the temperature sensor and make a good connection across the PLUGS pins with a 150 ohm resistor, (150 ohms = 0.150 kohms, so that = a temp over 100 deg C as far as the sensor output is concerned), I would expect the fan run normally as it would at high temperature. The plug would be seeing the same resistance as the temperature sensor would give..roughly anyway. I don't know if the engine has to be running or just with the electrics on, some systems will even run the fan when the key is out... BTW, good temporary electrical connections require pushing quite hard, (you will see this when you try measuring something with a multimeter, you wont get the correct reading just by touching the probes to the metal surfaces).

If this resistor test makes the fan work normally, then you have a bad temperature sensor, or the connection is not good between the sensor and the plug. You could try cleaning the connectors and refitting. Sometimes the wiring is broken and annoyingly intermittently works when you mess about with it! You can throughly check the sensor by removing it and sticking it in hot water and checking the temperature with a thermometer against the resistance at the terminals too, service manual describes this test..it will keep you busy if you do this..


A diagnosis of bmw K bike fan problems will give you a general idea of how these systems work, see
http://www.ibmwr.org/ktech/fan-diagnosis.shtml

If problems persist when the plug is seeing a 150 ohm resistance during test, it is likely a relay fault, my manual lists this part as,
ACM33211 M04/MATSU****A

You could try exchanging it for a known good one, or, if you sign up to be a xt660.com supporter then you can get the full service manual which details testing the relay. I don't know if you are comfortable testing electrical stuff, but just like the mechanical side, you have to start learning somewhere and it isn't as bad as it looks!

I strongly suspect the temperature sensor is on its way out, but you never know for sure till it's fixed!

Hope you get it sorted!

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idler

It could be several things: faulty coolant temperature sensor (as mentioned), tired/lazy fan relay, wiring harness/connector fault, ECU fault (let�s hope not).

A dicky coolant temperature sensor will often throw up an error code 21 and the engine trouble light will illuminate, but not always. The wiring/connectors can be checked visually for any abrasion and places where the fan circuit may be grounding. The fact it�s cycling on and off suggests a switching fault or intermittent short/open circuit. Is the pulsing regular or more random in nature? There is a test for the switching side of things - The relay, fan and to a certain extent its wiring can be checked in the diagnostic mode. It�s simple to do and is probably where I�d start first�

Enter the diagnostic mode in the dash by holding select and reset whilst turning the ignition on and holding the buttons down for 8 seconds (make sure kill switch is set to run when doing this bit). �DIAG� will appear in the display. You can use the select button to switch between �CO� and �DIAG� � you want �DIAG�. With �DIAG� in the display press select and reset together for 2 seconds to enter the diagnostic mode. Then flick the kill switch to the off position. You can now scroll up and down the list of diagnostic codes (checks) with the select (down) and reset (up) buttons. You need to find diagnostic code 51 which is the fan circuit test.

To run the diagnostic test just flick the kill switch to run and the ECU should provide a signal for the fan relay to energise and operate the fan. The test cycles the fan five times on and off. This will determine whether the ECU�s capability to switch the circuit, together with the relay operation is OK and if fan itself is doing what it should.

If all is good, then next have a look at the wiring and move on to the coolant temperature sensor as suggested. You can test simply for an open circuit at the sensor whilst still in the bike, but as I mentioned earlier the engine trouble light/error code 21 would already be indicating this if it was the problem. If the resistance of the thermistor is out of spec then the most accurate and informative method to test the resistance is by removing it and measuring the resistance range whilst it�s suspended in pan of water, heating it up gradually and taking measurements using a thermometer for cross-reference.

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Thanks for the replies I have just received the manual on CD so will have a look this weekend. I've maintained my Kawasaki's for the past 30 years so should be-able to sort it just needed a start point. All this new fangled error codes its getting like NASA

cheers swampy will post me finding when I sort it with a bit of luck

cleaned all the connectors, checked all the circuits. checked the fan feed all ok. Temp sensor checks out ok. Now the fan behaves and comes on when it should. looks like it was just a loose or corroded connection.
cheers for the advice

Fairly typical of an XT I'm afraid! Electrical gremlins can often be attributed to corroded connectors, dodgy connections or abraded wiring.

Glad all is now well.

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Glad you have it sorted.

As others have mentioned, application of some ACF-50 can help keep corrosion at bay. There is another product, which is about 2 thirds the price, Fluid Film, which may well be worth a look.

__________________
idler

I've give everything a good clean with GT85, this has preserved my bike's through most winters. Yamaha has gremlins? Kawasaki now there's a bike with gremlins. My 900r is 30 years old and I have had a gremlin or 2 with that one. I can sort that with me eyes shut now.