Noise from engine bay not turned ignition on

[Grainfoot]

When opening bonnet can hear what sounds like a very quiet fan, engine not been running ignition not switched on. It goes off after a short time. It does use battery power as I have been checking battery voltage during lockdown and can see voltage climbing again after it stops.
Anyone know what it is.

 

[hoggle]

Wh?

 

[Neil Nicholls]

Fuel pump ?

 

[Pauly]

Fan in LED headlights or fuel pump priming would be my guess ?

 

[Grainfoot]

Fan in LED headlights or fuel pump priming would be my guess ?

Dont have LED headlights, key not in ignition not sure why fuel pump would prime,!

 

[Lord Mfwic]

Dont have LED headlights, key not in ignition not sure why fuel pump would prime,!

It primes when you open the drivers door.

 

[Loz]

Dont have LED headlights, key not in ignition not sure why fuel pump would prime,!

Some VWs prime the lift pump in anticipation of you starting the engine so that the High-pressure fuel pump driven by the engine doesn't run dry. But there is also a water pump that circulates.

 

[Grainfoot]

Some modern VWs prime the lift pump in anticipation of you starting the engine so that the High-pressure fuel pump driven by the engine doesn't run dry.

Thanks, that must be it then.

 

[Loz]

Also, the Adblue pump primes and this also de-primes (removes the adblue from pipe) after you switch off.