Occasionally you may read a vehicle only to be greeted with a checksum warning. The warning says you may have a permanent DTC or the car may not be drivable. In 90% of scenarios checksum errors are harmless. Some of the possible causes of a checksum error are listed below: Harmless causes: You have an early BA with a blank VID block from the factory Someone used Ford IDS improperly and wiped the VID block You have a vehicle which was tuned with an early CAPA flash