I have a 2001 ML320 that is showing a PO422 code on the OBD2 scanner. That says Main Catalyst efficiency below threshold (bank 1). It sounds like there is a minor exhaust leak when its warming up, does this code mean I have a bad CAT or could it be a cracked weld in the system. Also is bank 1 the drivers side or passenger side of the car. Thanks for any info.