Make sure that the nozzle on your adjustable lance is pushed forward as far as it will go.
You may have a clog, kink or hole in the detergent suction hose. If clean, unkink or replace the hose. Use only the length of hose that was provided with the initial purchase of the pressure washer. Detergent suction will not function if more than one section of hose is attached to the pressure washer.
Remove the lance from the gun. If detergent is dispensed through the gun, the lance must be replaced. If no detergent comes through the gun, remove the 1" tapered detergent barb from the pump. Clean the barb, and make sure that the ball and spring are properly aligned with the tapered portion of the spring facing the ball. The ball should be on top of the spring.