Code p 0421 refers to warm up cat converter bank 1--efficiency below threshold ===causes ---cat converter---wiring---HO2S 2
( heated oxygen sensor)
code p 0431 refers to warm up cat conveter bank 2--efficiency below threshold === causes cat converter --- wiring---HO2S 2
as the same HO2S appears in the cause of the fault I would be inclined to change it first
the HO2sS sensor is the one in the exhaust manifold or before the cat converter
and 2 is in the front bank of a V engine
use the special socket when removing/ replacing these sensors as an incorrect tool is the main reason for wire failures on the sensors
SOURCE: I am getting a P0031, P1512, & P0421 code
P0031 - most likely pointing to a failed O2 sensor (bank 1 sensor 1 is located before the catalytic converter)
P0421 - failed catalytic converter or a failed O2 sensor
P1512 - intake manifold shutter valve is stuck - may be caused by the O2 sensor, but may not
I recommend replacing your O2 sensor first and see what happens
SOURCE: I have a 2004 Mazda
It can be hard to say which it is, because either one will trip the the code, but in this case I'd place my bet on it being the O2 sensor because it says "warm up" - the O2 sensor has to be up to temperature (around 900 degrees) to function. The computer watches for the O2 sensor to heat up in a certain amount of time, and if it doesn't get to temperature soon enough, the computer diagnoses a faulty heater for the O2 sensor and trips the code.
For the record, this would be the secondary O2 sensor, the one after the cat. That's the one that is used to determine cat functionality and efficiency. The primary sensor, before the cat, is used to fine-tune the fuel delivery.
SOURCE: Mazda mpv 2003 check engene light code p0421 warm up catalist ...
replace the air flow meter has this sounds like your problem.Good luck.
SOURCE: What are codes P1492, P0421 & P0431 on the
po421 warm up catalyst efficiency below threshhold bank 1, 431 same on bank 2..
SOURCE: SERVICE ENGINE SOON LIGHT CAME ON READS CODE P0431
Converter is not working as efficiently in Bank 1 and Bank 2 (two codes)...
P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
Symptoms: You will likely not notice any drivability problems, although there may be symptoms. The code may be more likely to occur after the engine has had numerous cold starts in the past 1-2 days.
Causes: A code P0421 may mean that one or more of the following has happened:
The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
A sparkplug is fouled up
Possible Solutions:
Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.
P0431 - Warm Up Catalyst Efficiency Below Threshold (Bank 2)
Basically this means that the oxygen sensor downstream of the catalytic converter on bank 2 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
Symptoms: You will likely not notice any drivability problems, although there may be symptoms such as a rough/hard idle when cold.
Causes: A code P0431 may mean that one or more of the following has happened:
The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
There is an exhaust leak
Possible Solutions:
Inspect for exhaust leaks. Next step is to measure the voltage at the oxygen sensor on Bank 2. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.
Hope this helps.
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