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Question:

Storey,
 Can you provide any insight into the error messages
that I read in? They were something along the lines of: “pressure switch
stuck high” and “vehicle moved”. I would believe that the first one is the
pressure switch that signals that the air tank is full and it might be a
good idea to replace that switch – even if it was a single intermittent
failure. I think I can ignore the other error.

Please note that I have not driven the vehicle with the EAS relay installed
since I cleared the error. I thought it would be safer to make the trip
back home with EAS disabled.

Answer:

The vehicle has moved fault is common and nothing to worry about. It is more
of a troubleshooting code than a fault code. A healthy EAS will throw the
“Vehicle has moved” code.

The pressure switch code can unfortunately point to a more serious fault.
First check the pressure switch ability to state change.
http://www.youtube.com/watch?v=a8Gdsc6880c&feature=player_embedded

Usually though, an intermittent pressure switch fault points to a failing
EAS Driver Pack.
http://www.rover-renovations.com/EAS-Valve-Block-Driver-p/anr3900u.htm

The driver pack is just a signal converter from low current logic to higher
current modulated signals for the valve block. They do fail over time due to
heat exposure in the compressor box. Even though the EAS driver pack does
not appear to directly handle the EAS pressure switch, the correlation
between the two is almost certain. Another good sign that the EAS driver
pack is going, is that the EAS compressor will cycle on and off about every
30-60 seconds. This behavior should not occur. The EAS compressor should run
until the tank is full and then stop until the pressure drops. It should
never cycle on and off so frequently. Try checking yours.