As urbancase said in his post below, it may be the tiny connector pin has broken. If it is, you take the valve out the bottom of the unit. It will require removing some of the hitch stabilizer parts but otherwise it is rather simple. For the tiny pin I used a needle bearing roller from a U-joint cross and bearing. I found one that was the same diameter as the hole in the valve parts it connects through and then ground it on a bench grinder to the needed length. Saved a trip to the dealer. Has worked perfectly for many years.
Pin is item #27 in diagram