Cooling fan electrical problem

Hi all, I am new to the site, had a WR250R now for nearly a year and really enjoying it. I have carried out a few mods so that it fits me better, mainly lowering and seat scalped a bit, the only thing I would moan about is its weight when I have dropped it a few times on trails.

I need some help with an electrical problem with the cooling fan, not long ago it wouldn’t come on and the engine was boiling so I eventually diagnosed the problem to a corroded terminal in the relay, I cleaned it and put loads of Vaseline around it, ran a check on the ECU 51 (fan relay) and it activated 5 times as it should – great I thought.

Next time out riding, every time the fan comes on so does the ENGINE WARNING LIGHT, fan goes off, amber warning light off. It sometimes gives fault code 21, but last time it recorded a fault but no code!

Another problem it didn’t have before is that when the engine is off/ignition on, the fan wont run, as soon as engine started again, fan runs along with the warning light.

I have cleaned the GREEN overheat sensor, played with the ECM but no difference, anyone gotta an idea??

Get rid of the Vaseline completely, that stuff is no good for electrical stuff it will cause short circuits and put dielectric grease in the connection it was in.
Your the first person I have seen use Vaseline instead of dielectric grease.

You have a bad connection or short in the relay you were working on.

Didn't realise that, I will clean the relay out and start again and report back.

PROBLEM – FAN TURNS ON WHEN ENGINE IS WARM (as normal) BUT THE ECU AMBER LIGHT COMES ON AT THE SAME TIME AND WHEN THE ENGINE IS CUT THE FAN STOPS EVEN WITH IGNITION ON.
Today I managed to spend some time working on the bike –

• Battery terminals good
• Cleaned the relay and used dielectric grease
• Battery is reading 12.5v
• Temp sensor – I think that has to be working as the fan comes on along with the ECU light when the engine warms up so I haven’t made a separate test on it.
• The earths seem fine
• Swapped the headlight relay for the fan relay and vice versa – both relays work ok in lights and both throw up same ECU light on with fan.
• Disconnected the battery and held + and – together to discharge the capacitors (cold reset)-THIS THEN BROUGHT UP ERROR CODE 21 iso OF 0, but after subsequent running of fan it displays a 0 error code
• 21---Coolant temperature sensor, open or short circuit detected. • Open or short circuit in wire harness. Defective coolant temperature sensor. Fault detected in ECU

Any more ideas gratefully accepted.

When was the last time you did anything to the coolant? How old is the coolant?

My old car used to throw a spike on the temp sensor when the cooling system had air bubbles in it. Maybe this is doing similar. Just a little air to throw off the thermostat?

Just a thought.

Hi, I replaced the coolant about 3 months ago, but the temp sensor seems to be working as the I let the engine run to warm up and eventually the fan comes on with the ECU light.

Dunlopsup wrote:

Hi, I replaced the coolant about 3 months ago, but the temp sensor seems to be working as the I let the engine run to warm up and eventually the fan comes on with the E9CU light.

Sounds just like my car. It was the smallest amount of air that caused the problem. I had to raise the radiator cap with a funnel or coke bottle cut down to have it be the highest point and force the air our cracking a valve on the top of the motor. I don't know how it's beat to tackle it with the WR but my best is there is some air in the cooling system.

Can anybody tell me if the TEMP SENSOR is the sensor with the green plug attached to it at the rear the engine - when I short this out it gives a RED OVERHEAT WARNING LIGHT.