P0420 fault code (brand new catalytic converter) - MINI Cooper Forum

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post #1 of 2 (permalink) Old Apr 20th, 2017, 04:25 PM Thread Starter
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P0420 fault code (brand new catalytic converter)

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Last edited by R56auto; Apr 20th, 2017 at 06:13 PM.
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post #2 of 2 (permalink) Old Apr 20th, 2017, 06:25 PM
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Originally Posted by R56auto View Post
Long story short .. purchased a lovely 07 plate 6 speed automatic mini from a (reasonably) local garage two weeks ago. The garage offered a free MOT and service with the vehicle which, incidentally, flagged up a fault in the catalytic converter (failed emissions test). The garage fitted a brand new catalytic converter to the car and the vehicle passed its second MOT. Approximately one week into driving the vehicle (~ 300 miles) up flashes the 'check engine' light. Using a code reader that I have myself, a P0420 code was displayed ("Catalyst System Efficiency Below Threshold"). I cleared the engine light and have continued driving the car with no noticeable difference in performance. The light has since come on again and so I'm wondering (1) what is the most likely cause of this? (2) is the car safe/ advisable to drive whilst I figure it out? and (3) would it be worth troubling the garage for the replacement of the o2 sensors? Given that the car has a brand new cat and has very recently passed its emissions test, I'm assuming that there isn't actually a fault with the cat and it must be a sensor fault/ air leak?? Any advice would be greatly appreciated.
the very first job on that for me would be timing chain get timing checked,, signs are a lot of chain slap noises when you blip the throttle on and off. (but they do stretch with no slap noises) i've replaced way to many cats because of t/chains allowing the valves to overlap to much and some of the fuel air mix gets dumped straight in to the cat this over heats it and the upstream 02 sensor,, even had a few that had melted the 02 sensor that badly it had fused the signal wire back to the ecu and ruined the ecu.. i've found this with those engines as early as 40k but others have lasted 100k but all lose power on the top end wont rev right.. also injectors fail dont atomise the fuel and that hurts the cat.. misfire on bank 1 or bank 2 faults codes and or cps implausible

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