P0421 code trigged.. does this OBD2 data confirm all ok?
Discussion
Posted a while back after my Mazda MIL light popped up with a P0421 code which points to a number of things, but possibly cat.
Consensus was reset code and drive on see if it reappears..
Does the 'completed' tests below confirm my cars computer thinks the cat is okay?
I'm not sure I've done enough drive cycles..
I'm confused by OBD2 apps and confirmation of whether 'readiness monitors' have completed necessary tests
Thanks for reading
Consensus was reset code and drive on see if it reappears..
Does the 'completed' tests below confirm my cars computer thinks the cat is okay?
I'm not sure I've done enough drive cycles..
I'm confused by OBD2 apps and confirmation of whether 'readiness monitors' have completed necessary tests
Thanks for reading
I think that's saying that everything the ECU is capable of testing has passed its tests since you last cleared the codes. If the MIL hasn't come back on I'd assume it's OK for now. It looks like P0421 is specifically an out-of-range lambda reading during warm-up which is probably more likely to indicate a (transient if it hasn't come back) sensor fault than an actual cat fault.
Edited by kambites on Sunday 7th August 11:59
From https://www.mazda3revolution.com/threads/2014-mazd...
Oct 3, 2021
Generally, inline engines only have one bank. Bank 2 only comes up when there is a second row of cylinders, and therefore a second exhaust manifold, cat, and another pair of O2 sensors. As this car has an inline-4, you will only see codes that reference Bank 1.
p0421 is an error that identifies that the difference between the two O2 sensors readings indicates that the Cat located between them has lost too much performance. This can have multiple causes, ranging from an exhaust leak, a bad O2 sensor, or a failing cat.
Changing the O2 sensors isn't a bad first step if you don't have the diagnostic equipment to really test them, as an O2 sensor is cheaper than a cat. One thing worth noting: be very careful with aftermarket sensors of any kind. They are cheaper for a reason, and just because it's new doesn't mean that it's good.
Assuming that the sensors you put in are good, the cat they are complaining about is going to be the one that is between the two O2 sensors.
Good innit
Oct 3, 2021
Generally, inline engines only have one bank. Bank 2 only comes up when there is a second row of cylinders, and therefore a second exhaust manifold, cat, and another pair of O2 sensors. As this car has an inline-4, you will only see codes that reference Bank 1.
p0421 is an error that identifies that the difference between the two O2 sensors readings indicates that the Cat located between them has lost too much performance. This can have multiple causes, ranging from an exhaust leak, a bad O2 sensor, or a failing cat.
Changing the O2 sensors isn't a bad first step if you don't have the diagnostic equipment to really test them, as an O2 sensor is cheaper than a cat. One thing worth noting: be very careful with aftermarket sensors of any kind. They are cheaper for a reason, and just because it's new doesn't mean that it's good.
Assuming that the sensors you put in are good, the cat they are complaining about is going to be the one that is between the two O2 sensors.
Good innit
My mechanic reckoned with ~50k its more likely a bad spot of fuel, or the O2 sensor going south, than the cat.
Mazda additionally found a TSB that they said can trigger this code so they applied some reprogramming to the ECU.
The engine light hasn't come on since, and its encouraging to think the computer has probably passed its tests!
Thanks.
Mazda additionally found a TSB that they said can trigger this code so they applied some reprogramming to the ECU.
The engine light hasn't come on since, and its encouraging to think the computer has probably passed its tests!
Thanks.
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