Volvo Repair: OBD does not reset, readiness test, scan tool

Question
I have a 1997 Volvo 850GLT with 117K miles.  Recently, the EVAP pump failed (again) causing the check engine light to come on.  I (again) purchased a resale EVAP pump from a VOLVO parts dealer and had my 'private' mechanic install it and reset/clear the code.  The check engine light has not come back on since the repair 3-4 weeks ago.  The issue is at state inspection, the read-out says "OBD not ready".  This failure has happened 3 weeks in a row.  I have driven the car 120 miles (failure) 180 miles (failure) total 300 miles.  We then used the scan tool at home to reset the system again (no codes were present).  Drove another 140 miles (3rd failure).   Any sugestions on why the OBD is not "ready?"

Answer
I know it may seem absurd, but you may not be fulfilling all of the conditions for the readiness test to complete itself.Make sure you take it out to the highway and bring it up to cruising speed along with around town driving. there is a valve that will stick open and cause moisture in the evap pump system, it is located on top of the engine towards the rear of the engine compartment.It has the hose leading to the pump,have its operation checked and replaced.You should stop having to replace the air pump.