Can fault codes be deleted simply by disconnecting the battery? If so, how long does the battery need to be disconnected for?

And by the way, what are fault codes? Do I need them?

 

Fault codes are codes issues by the car ECU when something isn't right. Yes, you need them - they tell you that something is broken or about to be. When the engine is not running properly, codes will lead you to the problem - without the codes you are often just guessing.

They can be deleted with some OBDII readers and with the Porsche Durametric program. You can probably remove some minor codes by disconnecting the battery for a few minutes (although I haven't tried) but the major codes won't disappear unless they are deliberately erased.