Raspberry pi 4 & fanshim

Good afternoon all.

I have two pi’s 4, each equipped with a fanshim.
Both work as expected with the python scripts that are provided.

However, I see a bizarre difference at startup between the two items.

When I power pi1, the fan starts turning during startup, until the service is started.
Then it stops, until the threshold is reached, and it kicks off as was intended.

When I power pi2, the fan DOES NOT turn at all during startup.
It starts turning as soon as the threshold is reached.

I think both pi’s are configured identically.

What am I missing ?
This kind of things makes me very curious !

Not critical at all, but bizarre !

Have a nice day.


Swap those two SD cards around, Pi 1 card in Pi 2 and vise versa. Then see if that behaviour follows with the SD card to the other Pi 4.
If it does, its software thats doing it. If it doesn’t its something going on with the hardware.

Exactly my plan for tonight.
I was planning to compare the config.txt files in those machines.

But first… let’s finish this bottle of red first !

Thank you for the reaction.


So, after the test you suggested… it should be hardware-related.
Strange .

I will give it some more time later on.


I would reattach the Fan Shims, maybe even swap them on the two Pi’s. It may just be a connection issue.

Thanks again for your suggestion.

I found that the shim that did not run turn the fan at startup had a bas 3.3V connection.
“Solved” it by applying a tiny bit of “electric paint”.

Strange that there was only an anomaly at startup, and that the shim was fully functional once booted.

Thanks for staying with me.
Have a nice weekend !


Electronics can do some really puzzling things some times.;)
Looks like it’s going to rain all weekend here, according to Environment Canada anyway.
I’ll find something to tinker with anyway. We are no strangers to rainy days here. I’m right on the sea coast.