Starter motor & fan weird inter-related behaviour: any ideas pls??

Mikey E

new rider
Joined
Oct 8, 2025
Messages
1
Location
E Midlands
Hi Everyone

First time posting.

I've had my '19 plare 401 Vitpilen for about a year now. Love it, but, after about 9 months it developed a weird problem, I'll try to summarise below:
When slowing down or idling in traffic, especially when the weather is hot, the fan starts up, then goes off after a while. All normal.
However, after the second or third time, when the fan kicks in at idle, so does the starter motor(!!). It makes an embarrassing racket and I'm sure it does the starter motor and battery no good either.
But if you rev the engine a bit, the starter motor stops, only to re-start as the engine returns to idle.
The fan seems to do its nomal thing and cool the engine enough then turn off.
But as the fan comes on more times during a ride then the starter motor gets worse, in that you can't stop the starter by revving the engine, so the starter is going all the time the fan is running...
Fan and starter both stop when you turn the bike off.

Bike is kept on trickle charger overnight and had a new battery after this started happening. It made no improvement.
So, I'm thinking it's something that's related to battery voltage somehow, since its OK when the bike is first used/cold (battery is full), but as the fan gets used it must be dischaging the battery a bit until 'something' happens and the starter motor comes on.
And revving the engine temporarily increases the battery voltage as the alternator output increases with speed.
Up to the point that it can't keep up with the discharging battery.

I get the engine warning light on the dash, and the OBD reader says the following error codes:
P0691 Fan 1 contol circuit low
P0616 Starter Relay Circuit Low
P0615 Starter Relay Circuit
P0480 Fan 1 Control Circuit
Clear the error codes with OBD reader and they come straight back sometimes, other times after its run and the 'fault' happens.

Has anyone else experienced anything like this, or am I just really unlucky??

As part of trialling anything to see what happens, we removed the starter relay when the bike was running and really hot after a good run on a hot day, and (somewhat obviously) the starter motor didn't run unintentionally, no matter how many times the fan cycled. We also tried swapping the relays around (some have the same part numbers) and it made no difference.

Now this is the really weird bit - with the engine stopped, and no starter relay fitted, if you pressed the starter button the bloody fan came on!!!

At a bit of a loss, have cleaned all terminal for starter / solenoid /relay. All were OK anyway. Took switchcube apart and no signs of corrosion there.

Bike has been wet a few times but is kept clean and stays in a dehumidified garage overnight.

Hope there are some electrical geniuses out there!!

Many thanks for any bright ideas

Michael
 
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