[Lelebebbel]

Trying to figure out why my fans are suddenly stuck on after service. I did a major annual, belts, valves, hor. head gasket, motolectric wire kit and FH020A R/R.
Before all this, my fans would turn on for 2 seconds on ignition on and then click off. Now they just stay on. I can't figure out where the fan relais are on this bike - there would have to be 2 of them as the fans can turn on individually, no? Or is this handled directly by the ECU (as the diagram implies) without any relais, in which case there must be something going on with my coolant temp sensor?

 

[mlukason]

You didn't, by any chance, momentarily hook up the battery backwards? Even for a split second?
That sounds like a fried ground in the ECU. If so, connect the ground in the diagnostic plug to a good ground on the bike and see if that takes care of the issue.

 

[t_bare]

You didn't, by any chance, momentarily hook up the battery backwards? Even for a split second?
That sounds like a fried ground in the ECU. If so, connect the ground in the diagnostic plug to a good ground on the bike and see if that takes care of the issue.

This is what I'm thinking.

t_bare

 

[Lelebebbel]

Those replies nearly gave me a heart attack... I never did reverse the battery, good to know that this is what can happen though.

I found a broken wire at the temperature sensor plug. A previous owner had done a really shoddy soldering job, and it must have cracked under the rubber grommet when I pulled it apart. Everything works now.


Small follow up question though: After I turn the ignition on, the fans stay on for a good ~10 seconds or so before turning off. I can't totally recall if this was the case before I pulled stuff apart, but in my mind they were only on for maybe 2-3s after turning the key?

 

[xracer]

does the bike start?

 

[xracer]

check the earth wire to the ecu. its bolted to one of the ecu mounting bolts

 

[t_bare]

Those replies nearly gave me a heart attack... I never did reverse the battery, good to know that this is what can happen though.

I found a broken wire at the temperature sensor plug. A previous owner had done a really shoddy soldering job, and it must have cracked under the rubber grommet when I pulled it apart. Everything works now.


Small follow up question though: After I turn the ignition on, the fans stay on for a good ~10 seconds or so before turning off. I can't totally recall if this was the case before I pulled stuff apart, but in my mind they were only on for maybe 2-3s after turning the key?

Great news. If you have a low temp fan switch kit installed it will continue to run after you shut off a warm bike, also the assembly of the low temp kits were kind of questionable quality.

t_bare

 

[duc96cr]

I found on some Ducatis, my S4RS for one, the ecu ground is poor. I ran a wire from the ecu ground to the battery grounding point to make sure I have a solid ground. I also run a wire from any other ground, such as a frame ground, back to the battery grounding point. This is called a Single Point Ground. It helps if you have a bike with a weak electrical system.

 

[C-simian]

A fried relay caused my fan and lights to stay on in my ST4S. Replaced the relay and it's been good so far. Just a possibility.

Ron