Is your location error getting worse ? (i.e. as you add miles to the car, is the offset increasing ?) That means the GPS may need to go thru a calibration routine ( I haven't tried any of this yet. ) The error could be accumulating because some built-in systems (not portables like Garmin of course) use a combination of (car's) speed sensor and satellite. This allows the GPS to cover short gaps in updates from the satellites (like going thru a tunnel, etc). But if the speed sensor is off, the location is "shifted", naturally. Most built-in systems are smart enough to "correct" (reset) the error upon the next sync with the satellite(s).
2011 Silver SL+QC [Mfg: 11/2010] 36mo/15k LEASE
06Jun2013 Status [28.5 months][34,173 miles][11 bars]
Lost CapacityBar 6/6/13 @34,173 miles while in LEAF Battery Monitor: 83.41%, 71.4F (avg); cool overnight;