P0420 Code reading
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P0420 Code reading
Alright so earlier this week I was getting 2 codes for bad O2 sensors because the previous owners swapped the headers and kept the headers with no catalytic converter at all. So I went online and ordered a Magnaflow 22628 Catalytic converter , an o2 sensor extension harness , and 2 BRAND NEW o2 sensors from auto zone. I did all this, then installed it, and reset the computer so my check engine light would go off and went to pass smog. About 3 days later I got a new engine code, P0420 (Catalyst System Efficiency Below Threshold). I currently have no exhaust passed the catalytic converter, do you think that could cause this code? If not, what could? I never had this code before I put the catalytic and new o2 sensors on. Input? Thank you 
Joined: Aug 2003
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Re: P0420 Code reading
Kitty prolly doesn't play within the ecu's happy zone. Quick fix: mechanical O2 sim on the DS O2 sensor, reset code, and drive on.
Mechanical o2 simulator: buy 2 spark plug non foulers, drill one out with a 1/2" bit, screw that one on the undrilled one, screw that apparatus into the o2 sensor bung, install o2 sensor on apparatus currently screwed into exhaust pipe.
[exhaust pipe][non fouler][drilled one][O2 sensor]
Won't pass a visual inspection, but it'll pass a smog test.
Source: NV only requires a smog check, and I've been running with one since 08.
After actually reading your post instead of skimming, chances are it's the autozone o2 sensors. Can't speak for 6th gens, but the d17 doesn't play nice with non-OEM/denso sensors.
Mechanical o2 simulator: buy 2 spark plug non foulers, drill one out with a 1/2" bit, screw that one on the undrilled one, screw that apparatus into the o2 sensor bung, install o2 sensor on apparatus currently screwed into exhaust pipe.
[exhaust pipe][non fouler][drilled one][O2 sensor]
Won't pass a visual inspection, but it'll pass a smog test.
Source: NV only requires a smog check, and I've been running with one since 08.
After actually reading your post instead of skimming, chances are it's the autozone o2 sensors. Can't speak for 6th gens, but the d17 doesn't play nice with non-OEM/denso sensors.
If you think a good mechanic is expensive, try hiring a bad one
Joined: Dec 2011
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Non OE sensors? NTK or DENSO (whichever was in there originally)!!!! Get rid of Bosch.
Non OE cat:
OE is preferred, (Best quality)
CARB/California certified is 2nd choice.
49 state is just not good enough for these cars sometimes. (Not even a choice at work.)
But wait, read on....
Is there seriously no exhaust pipe on the rear of the cat? Sensor is too close to fresh air.
There is a good chance that alone is causing the code due to fresh air reversion being picked up by the rear sensor. You need to have a pipe with zero leakage on the back of the cat, I'd say 3 feet or longer.
Make that step #1 and see how it goes.
Non OE cat:
OE is preferred, (Best quality)
CARB/California certified is 2nd choice.
49 state is just not good enough for these cars sometimes. (Not even a choice at work.)
But wait, read on....
Is there seriously no exhaust pipe on the rear of the cat? Sensor is too close to fresh air.
There is a good chance that alone is causing the code due to fresh air reversion being picked up by the rear sensor. You need to have a pipe with zero leakage on the back of the cat, I'd say 3 feet or longer.
Make that step #1 and see how it goes.
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