Hello, I just recieved my Speed Tuning ECU for my 99 A6 2.8. alas it causes a check engine light, when I swap in my old ECU the light goes away.
Can anyone give me some tips on how to go about fixing this?
thanks,
Rodel

You need to scan the ECU for fault codes and post them up. Once you have the codes, we can try to help you out.

+1 on what Upstate said.
Then once you have the codes you should contact your vendior for support. I mean heck, this is a brand spanking new device so they should have the knowledge to help you.