MY 1999 TRACKER 4WD LIGHT FLASHES WHEN OCCASIONALY LOCKS IN, BUT USUALLY HAS NO 4X4. I BELIEVE THE ACTUATOR IN THE FRONT AXEL LEAKS AIR SO DOES NOT STAY ENGAGED. THE PUMP RUNS FOR ABOUT 10 SECONDS AND TURNS OFF WITH OVER 10 PSI PRESSURE BUT DOES NOT ENGAGE AXELS. WHAT IS THE PROCEDURE TO TEST THIS SYSTEM? JIM