If it has a relief valve it will be in the lift valve circuit somewhere. If it were me, I would probably remove the banjo bolt from the lift housing end of the pressure line. swing the line out of the way enough to get a rubber tipped air nozzle sealed against the port. With bare lift arms (nothing attached) set the controls to full raise and introduce a blast of compressed air into the port. If things in there are working the lift arms will pop up. If they don't, and you hear the air escaping inside, then you know have a problem in there. If they do pop up, then you're back to the pump and/or supply.