OBD II code P0420
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Junior Member
Joined: Sep 2011
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From: South Carolina
OBD II code P0420
What does "Catalyst system efficiency below threshold (Bank 1)" mean.This is what my OBD II code scanner reads when my check engine light is on and I need to know what it means.Thanks.
Senior Member
Joined: May 2010
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From: Some random Drop Zone on FT Bragg
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
Goes on to list possible causes, solutions and other info...
Senior Member
Joined: Jan 2011
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FWIW, if you're also getting codes that both banks are running lean, diagnose your fuel system first. I had all three codes and my fuel pump wasn't performing well. After putting in a new fuel pump, the lean conditions were corrected, and my cat is now performing normally.
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Joined: Aug 2012
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From: Tejas
Try this first...
It means you've got a bad catalytic converter. I didn't want to spend money on my 10 year old truck on a new converter, so I tried this $5 solution and it worked! Took more time going and buying the defoulers than the work to get it installed. Oh yeah, rent the o2 sensor removal tool when you're buying the defoulers. Several thousand miles and still no check engine light:
