So I have a 2007 Mini Cooper base that has already cost me more than anticipated (and more than its worth) and now I just got a CEL which I reset but less than 200 miles after its back. P0420 I believe it's Bank 1 efficiently low or something like that. Anyway I've already read online this usually means you need a new cat. Sometimes it's an 02 sensor, with wishful thinking I used my graphing obd scanner (phone) and saw that bank 1 Sensor 2 was nice and steady but bank 1 Sensor 1 wouldn't give me anything appeared to be dead, is that indicator of something or no? Also could just be me but i think it smells slightly rich too. Any help is appreciated, I don't want to spend a fortune on a new cat for a car that is already over budget. Thanks in advance

 

The pre-cat sensor is used to determine your air to fuel ratio. If this fails then the car will probably default to a rich condition to protect the engine.

I'd replace the sensor.