P0420 Code - Catalytic Converter or O2 Sensor?
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P0420 Code - Catalytic Converter or O2 Sensor?
The car (2010 Accord 4 cylinder) has about 130k miles on it and a while ago a P0420 code was set. I cleared it and all was well. Now 10k miles later the P0420 code has been set again. There are two confusing things.
(1) After warming up the catalytic converter by driving for about 30 mins on the highway I read the following temperatures with an infrared thermometer:
converter input (read directly on the top O2 sensor - accessible from top of engine bay) ~ 390 degF
converter output (read directly on the bottom O2 sensor - also accessible from top of engine bay) ~ 330 degF
A working cat should have a much higher output temperature than input.
(2) Using OBD Fusion to monitor (log) the O2 sensor voltage while driving I only see activity on Bank 1 sensor 2. Bank 1 sensor 1 (which I'd have thought is the cat input O2 sensor) shows constant 0V. But the short and long term fuel trims on Bank 1 do vary with time so perhaps Bank 1 sensor 2 is the cat input O2 sensor since trims cannot be computed if the cat input sensor is not working.
Anyone have any comments? The likelihood of two simultaneous failures (i.e., both the cat output O2 sensor and the cat itself) seems low but I cannot interpret these results any other way. Perhaps I need to take those temperatures again at different spots?
(1) After warming up the catalytic converter by driving for about 30 mins on the highway I read the following temperatures with an infrared thermometer:
converter input (read directly on the top O2 sensor - accessible from top of engine bay) ~ 390 degF
converter output (read directly on the bottom O2 sensor - also accessible from top of engine bay) ~ 330 degF
A working cat should have a much higher output temperature than input.
(2) Using OBD Fusion to monitor (log) the O2 sensor voltage while driving I only see activity on Bank 1 sensor 2. Bank 1 sensor 1 (which I'd have thought is the cat input O2 sensor) shows constant 0V. But the short and long term fuel trims on Bank 1 do vary with time so perhaps Bank 1 sensor 2 is the cat input O2 sensor since trims cannot be computed if the cat input sensor is not working.
Anyone have any comments? The likelihood of two simultaneous failures (i.e., both the cat output O2 sensor and the cat itself) seems low but I cannot interpret these results any other way. Perhaps I need to take those temperatures again at different spots?
Fish Twig
Joined: Nov 2005
Posts: 15,554
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From: Still hunting that foo up there
Re: P0420 Code - Catalytic Converter or O2 Sensor?
The thing is that when you reset or clear codes you have to go through a drive cycle to have your ecu in 'ready' and thats probably why you didn't get that error until it finished checking the drive cycles. your secondary o2 should provide SOME data still and is likely either a wiring issue or the sensor went bad, likely the sensor since the car is still new.
Honda-Tech Member
Joined: Mar 2004
Posts: 4,834
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From: Looking for SloMofo....
Re: P0420 Code - Catalytic Converter or O2 Sensor?
The car (2010 Accord 4 cylinder) has about 130k miles on it and a while ago a P0420 code was set. I cleared it and all was well. Now 10k miles later the P0420 code has been set again. There are two confusing things.
(1) After warming up the catalytic converter by driving for about 30 mins on the highway I read the following temperatures with an infrared thermometer:
converter input (read directly on the top O2 sensor - accessible from top of engine bay) ~ 390 degF
converter output (read directly on the bottom O2 sensor - also accessible from top of engine bay) ~ 330 degF
A working cat should have a much higher output temperature than input.
(2) Using OBD Fusion to monitor (log) the O2 sensor voltage while driving I only see activity on Bank 1 sensor 2. Bank 1 sensor 1 (which I'd have thought is the cat input O2 sensor) shows constant 0V. But the short and long term fuel trims on Bank 1 do vary with time so perhaps Bank 1 sensor 2 is the cat input O2 sensor since trims cannot be computed if the cat input sensor is not working.
Anyone have any comments? The likelihood of two simultaneous failures (i.e., both the cat output O2 sensor and the cat itself) seems low but I cannot interpret these results any other way. Perhaps I need to take those temperatures again at different spots?
(1) After warming up the catalytic converter by driving for about 30 mins on the highway I read the following temperatures with an infrared thermometer:
converter input (read directly on the top O2 sensor - accessible from top of engine bay) ~ 390 degF
converter output (read directly on the bottom O2 sensor - also accessible from top of engine bay) ~ 330 degF
A working cat should have a much higher output temperature than input.
(2) Using OBD Fusion to monitor (log) the O2 sensor voltage while driving I only see activity on Bank 1 sensor 2. Bank 1 sensor 1 (which I'd have thought is the cat input O2 sensor) shows constant 0V. But the short and long term fuel trims on Bank 1 do vary with time so perhaps Bank 1 sensor 2 is the cat input O2 sensor since trims cannot be computed if the cat input sensor is not working.
Anyone have any comments? The likelihood of two simultaneous failures (i.e., both the cat output O2 sensor and the cat itself) seems low but I cannot interpret these results any other way. Perhaps I need to take those temperatures again at different spots?
Your OBD tool is generic and doesn't know what is being monitored,it is simply supplying you with SAE J1979 data.
This vehicle does not have a Bank 1 Sensor 1,oxygen sensor. It is an Air/Fuel ratio sensor. Its voltage varies very little if at all, consequently PID data needs to be in amperage form and even then the transitions are minute.
However you can be sure the sensor is working as long as the short term trims are oscillating as they are a direct reflection of the AF sensor reading. (you would also have a code for an AF sensor and the catalyst monitor would be suspended and there would be no cat code)
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