I presently am receiving two error codes, 4-3-5 and 4-4-3, one which indicates
                  that the O2 sensor is slow to respond, and the second, that the catalytic
                  converter efficiency is poor. I recently experienced flooding problems during
                  extreme cold conditions, and thus the above problems began. The 850 Turbo
                  presently has 200,000 km thus the front O2 sensor definitely needs
                  replacement, but would you suggest a gas line detergent to clean the catalytic
                  converter? If so, can the cleaning product harm any other flue system
                  components in the process?

                  Thanks...

                  --
                  BrianB

                  Try running the car hard for a few minutes. Think 3500 rpm or more. Then
                  replace the front O2. That may solve your problem.