According to who/what though?. In the Suzuki workshop manual.pdf, a fault with the servo/valve will put the bike into fail safe or limp mode. I'll disconnect the servo with the Yoshi fitted, then check what happens if I leave the ECU wire intact (just to see). Maybe it's wrong, but here it is in B&W: Read it again. The Fail-Safe Mode is fully open. so if the valve is not there or no signal is not received from the servo, the ECU will default to the fully open setting which has no impact on the running of the bike. The FI light will come on to let you know the ECU has defaulted one of its settings to the fail-safe value, but this won't slow the bike down as the valve is non essential so the fail-safe mode value of fully open won't be a problem. EDIT: Here's a photo of my GSXR with its FI light on... no lack of power here The ECU has simply assumed the SET valve to be fully open (which is is) and which it would be at revs over 5k rpm.