New to the site and have only read about tuning, never done any prior. I'm doing along of reading and want to try to start with a modified tune and tweak it to gain knowledge. My question is how do the last 2 letters of the ecu part number work. Must the numbers match for the file to work?

I have a spare ecu, must it have the same letter codes as my current ecu for it to work in the car?

The car is a 2004 VW Jetta 1.8t awp.

They're pretty much all interchangeable. I like tuning my HN over my PL. Its just different definitions that you're working with.

i briefly covered this on my post in another forum.

Thanks, will look through it when i get a chance.