[Stefo]

I have a 2017 M240xi with 45,000 miles. The check engine light went on today with a error code of P0420. Which is the 'Catalyst System Low Efficiency'. More specifically, a problem with the catalytic converter or the oxygen sensors.
I find it hard to believe that the CAT's are bad on this car, especially when my Infiniti G35 had 210,000 miles with the original CAT's and oxygen sensors.
I have since cleared the error. Will see if it comes up again.
I will be adding some fuel injector/fuel system cleaner to see if it helps.
Any suggestions appreciated.

[MarcoZandrini]

Get the OBDFusion app for your phone or tablet. If your device is iOS then get a wifi adapter to plug into the obd2 port. If it's android you need to buy a Bluetooth adapter. You need to look at the o2 sensors' responses to changes in engine speed and load. The sensor may be lazy or bad. Also, the emissions system has a longer warranty than the rest of the car or the drivetrain.

[Stefo]

The P0420 code came up again after I cleared it. After reading the warranty book it states that my state which I live, is one of many that have a 7 year/70K mile emissions warranty and the catalytic converter is covered. I brought it to the dealer and they said that its out of warranty and it will cost $199 to examine the code and diagnose it. They came back 2 hours later and said it was the catalytic converter and it be covered under the emissions warranty. They cost of the CAT is approximately $2,000 if it wasn't. Made an appointment for next week.
Thanks for the help!

[germanlight]

if the p0420 comes again, please consider o2 sensor cleaning process.

[Dom147]

Downstream sensor is likely bad. Replacement is incredibly easy.