MarkConrad

Im new to the S4 world and I'm trying to figure out what kind of ecu box a 2000 has and what is compatible with it. Ive seen A and M Boxes and dont know what that means or what would go with my car.

Jeff Vader - boscoj

Look on the sticker on the ECU it's the last character. Corresponds with build date.

Silver S4urfer

Think of "A" and "M" designations as a run designation. A 2000 S4 could have either and you will need to crack the case that protects the ECU to determine which you have. You can find instructions on how to do this at APR's web site. If you are going to chip your car with lets say an APR "tunned" ECU or by sending yours in, this Box designation lets them know what software load to run.

JagoS4

should be an "A" box