Our 7140 flashed the five this fall...but it's really a "S".  Forget what it specifically stand for, but it's most likely the draft sensor(s) that tell the hitch how hard it's pulling.  Most people (us too) get the elimination kit, which consists of a two null- connections to complete the circuits.  I remember it costing about $150, though.  Took about 30 min for the tech to fix; had to have a special electrical connection crimping tool to make the appropriate connector.

When we had the error code while plowing we couldn't get the hitch to go down with the rocker switch at all...you could sporadically get it to go down with the lever, but unreliably.  EDIT: Your manual has a pretty good section that covers every code it can flash.

John