BMW relies heavily on the CAT for emissions reduction of HC, CO, and NO. Replacing the CAT might just do the trick... but if you spend one hours worth on labor ($50-$60hr), you can get a smog check repair station to verify this for you. This way you'll save money in case the CAT isn't the problem.
Smog check repair stations usually charge a 2 hour minimum to diagnose a smog check failure. If this failure appears simple to the smog technician you might get away with one hour.
posted by SmogTips Support
