Edsel, If you haven't already, the online Mercedes Forum https://mbworld.org/forums/ is a good resource for all types of MB vehicles. This site has a large international following. As you indicate our xfires were made by MB and are very similar to SLK320 class R 121. This site has a section for these models. I also recently bought a diagnostic code reader on on Amazon for 159usd made by Launch (Creader Elite V2.0) . This version is specifically for MB and Maybach model cars and Sprinter trucks. I beleive the unit I have only covers more recent or newer MB models. I plan on using this code reader for my MB E350 sedan. Try searching the different Launch units to see if there are models that support older MB vehicles. I doubt there will be a version available specifically for the xfire. The MB SLK R121 version should be capable of diagnosing the ECM for a 3.2L engine or automatic transmission,