HDClown

Things like the radio coding are stored in the ECU right? What about other things that may be different in your original ECU as compared to the newly purchased (or used) ECU you purchased to be chipped?

ReyHey

Cruise Control is one.

Steveo369

When I got my spare ECU w/ chip, I sat down with Vag-Com and went through every controller I could access.

I wrote down the coding and workshop code for each controller from my stock ECU. I then plugged in the chipped ECU and changed all the settings to match those found in my stock ECU

This is probably overkill, and many of the settings were the same, but it only took about an hour or two, and gave me more peace of mind. I would say it's more important if you're buying an ECU that doesn't exactly match, i.e. putting a 98 ECU into a 99 or coding a TIP ECU to work on a manual car. Probably not as important if you're buying the ECU new from the tuner and it's pre-matched to your vehicle.

Note, if you're planning on taking your chipped ECU in for service and "hiding" it from your dealer, (not personally recommended, but to each their own) make sure you clone the workshop codes. this is an instant tip off to the dealer that your ECU is swapped, i.e. PDI wasn't performed by them.