Determine the faulty part by following the "Inspection procedures when BMU P0AA6-00: Insulation Resistance Drop Detection Diagnosis is set." (Refer to DIAGNOSIS CHART FOR DTC No. P0AA6-00) and deal with it.
The trouble can be an intermittent malfunction (Refer to General Information - How to Use Troubleshooting/Inspection Service Points, How to Cope with Intermittent Malfunctions HOW TO COPE WITH INTERMITTENT MALFUNCTIONS).