from memory it can vary depending on when you want it to really.. You need a guage/tool/footpump to fit to see when it operates (at least during installation) vs your engine revs and at what psi/bar level you have of charge. I have mine set to come on at around 0.3bar/4psi. (running stage2 8-9psi/0.6bar) However it is one of those things that is worth talking to your preferred local tuning specialist about in detail. I notice you are from Denmark.... normally we would suggest you talk to Vince at Stealth in the UK. So maybe worth trying him for a call at least, if your happy to If you a