As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MODE C TRANSPONDERS READ 500 FT HIGH 99 PERCENT OF THE TIME (IN CRUISE). TROUBLESHOOTING IN PROCESS, WILL AMEND FORM WHEN DETERMINATION OF CAUSE 8/22/08. RAN PITOT/STATIC SYS TO 45,000 FT AND CHECKED OUT PUT OF TRANSPONDER SYS WITH ATC601 TEST SET AND INDICATED NORMAL, REMOVED AND REPLACED CTL92 CONTROL GROUND CHECKS GOOD, PERFORMED OPERATIONAL TEST FLIGHT AND ATC REPORTS NO ABNORMALITIES.