Diagnosing Stored Fault Codes to Help Avoid Repeat Repair Visits. Analysis of FASTA data and repeat repair visit reports indicates that there are many fault codes that are stored in the above vehicles, but they are not diagnosed to identify their root cause. Fault codes that are not diagnosed to find their root cause can lead to a repeat repair visit to the workshop by the customer. Where diagnosis (vehicle or short test) with ISTA has already started, it is important to diagnose the fault code(s) listed below (when they are stored in the vehicle) during the current workshop visit. This will help lead to a reduction in workshop repeat repair visits and higher customer satisfaction.