I had this exact same problem last summer, everything operated fine but it would not auto lower.  The outside height sensors had failed.  I put in new ones and nearly instantly they failed.   So I ran a new 12 volt wire to power the solenoid valves through relays.   The system wiring now activates only the relays, all has been fine since.   Still not sure what was going on, a voltage spike or ????  But the system power was frying the height sensors.  I cooked 4 of them, when I went to 5 & 6 I installed the relays.  If you figure anything else out, please let me know.