2001 chev s-10

po 440 code ,keeps coming back…replaced silonoid valve on intake, and gas cap… how does this system trigger a code?
also
can a scan tool code reader be plugged in and on while the vehicle is RUNNING?

http://www.obd-codes.com/p0440

a 440 code can be front pump look under right side of motor serp belt drives it the car can run fine with out it as long as the pump dosnt sieze and yes a good scanner will check the car while running