VXOC Astra-J/GTC

Full Version: fault code 0420
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i have a 2014 astra j gtc 1.4t, i keep getting a p0420 fault code , any ideas on what i should be looking for to rectify whatever problem it is , as soon as i clear the code my engine runs perfectly  then 2-3 days later it gets a misfire at about 2500-3000 rpm , thank you in advance