P0420 - Catalyst System; Bank 1: Efficiency Below Threshold in Third Generation Legacy (1999 - 2004) Posted February 16, 2012 For my issue, i replaced the rear O2 sensor and no more check engine light! Yeah! I recently got the two codes when having my car scanned. I got the P0420 code as well as P0020. To fix the P0420 I will check fixing that code with an Oxygen Sensor. Im not sure what it will take to fix the P0020 code, I have to research that more. Did your cruise control light flash while your check engine light was on??
P0420 - Catalyst System; Bank 1: Efficiency Below Threshold
in Third Generation Legacy (1999 - 2004)
Posted
I recently got the two codes when having my car scanned. I got the P0420 code as well as P0020.
To fix the P0420 I will check fixing that code with an Oxygen Sensor.
Im not sure what it will take to fix the P0020 code, I have to research that more.
Did your cruise control light flash while your check engine light was on??