As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI STBY ATI IS NOT INDICATING ZERO ANU ON THE GROUND. AIRCRAFT RETURNED TO GATE. MAINTENANCE GROUNDED AIRCRAFT. PERFORMED ISU ADJUSTMENT/TEST PER ALTITUDE LEVEL AND REMAINED SO AFTER CYCLING POWER NO FURTHER DEFECTS NOTED PER ISU AMM SUPP 34-13-09. AIRCRAFT RETURNED TO SERVICE.