It doesnt click or lock in, just pops back out.

 

mine pops in, and pops out when you turn it off, though there isnt /that/ much travel distance. the light under the subtank word lights up when its in operation. so even if you push it in and youve got no fuel in there, it wont light up, or if the main tank is too full, it also wont light up.. and if you leave the subtank pump on, without moving the switch, the light will extinguish once there is no fuel left in the sub, while the switch is still pushed in.

so the light really only represents the fuel pump running.

hope that explains it.

 

If yours is a DI it maybe worth disconnecting the battery for 15minutes to reset the control unit, I had to do this many years ago out on the road to get back square one.
Worth a try.

 

Also anytime you start the vehicle, I believe a tiny amount of fuel is sent from the sub to the main.

everytime you start the car the tranfer pump automatically transfers fuel into the main tank for 10 seconds....

I can confirm this behavior is happening on my 2018 GCC spec Y61. Firstly, I thought this is an issue. But it makes perfect sense from the safety point of view: dashboard computer must be able to diagnose and fire up a warning light “aux pump oopsie” when you start your journey. Finding out that oopsie in the middle of desert isn’t that nice.

Photos from June 9 and June 19 attached.

Well, it seems it messes my fuel consumption measurements a little bit, probably adding an error of nearly 1 liter per 100 km.

 

The pump runs for around 5 seconds on start up, the more short runs you do the more those 5 seconds mount up. If you don't top up the sub at each fill you eco numbers will not be accurate.