CEL code P0420...a little perplexed
CEL code P0420...a little perplexed
a few days ago i had a CEL come on. Took it to autozone where they pulled code P0420 (reduced catalyst efficiency, bank 1) possibly a bad 02 sensor. Whats confusing is that when the lady pulled the code we got 2 codes, both of P0420. Why would it have two of the exact same codes coming from the ECU?
also i made a road trip to Indiana and when i pulled into Ohio for the night the CEL went off by itself
hasnt showed up since i got here but the problem still plagues my mind...
also i made a road trip to Indiana and when i pulled into Ohio for the night the CEL went off by itself
hasnt showed up since i got here but the problem still plagues my mind...
CL Community Team
Joined: Apr 2004
Posts: 17,318
Likes: 203
From: Miami, Florida
One code is the P0420 and the other code is what is known as a pending code. Pending codes are ones that if you hooked up an OBD2 scanner might show up, even though the check engine light is not lit. Generally, you need 40 times of the same issue showing up before the check engine light will show up under certain sensor ranges, what I like to call the fringe zones, but if they go beyond those fringe zones immediately, the light will come on. Otherwise, you need to wait about 40 times.
However, once the light goes on, the pending code will still stay there.
Generally, if the situation has resolved itself, where no more pending issues, the light will go off after starting up the vehicle 3 times or could go off for other reasons.
P0420 was very common where I used to live in Mexico City, largely because of the gas, but could also occur due to poor combustion caused by hot air devoid of oxygen (of which living at that high altitude was to the tune of 25% less oxygen).
What you probably got was a temporary sensor issue due to poor combustion rather than a bad O2 sensor or cat.
However, once the light goes on, the pending code will still stay there.
Generally, if the situation has resolved itself, where no more pending issues, the light will go off after starting up the vehicle 3 times or could go off for other reasons.
P0420 was very common where I used to live in Mexico City, largely because of the gas, but could also occur due to poor combustion caused by hot air devoid of oxygen (of which living at that high altitude was to the tune of 25% less oxygen).
What you probably got was a temporary sensor issue due to poor combustion rather than a bad O2 sensor or cat.
One code is the P0420 and the other code is what is known as a pending code. Pending codes are ones that if you hooked up an OBD2 scanner might show up, even though the check engine light is not lit. Generally, you need 40 times of the same issue showing up before the check engine light will show up under certain sensor ranges, what I like to call the fringe zones, but if they go beyond those fringe zones immediately, the light will come on. Otherwise, you need to wait about 40 times.
However, once the light goes on, the pending code will still stay there.
Generally, if the situation has resolved itself, where no more pending issues, the light will go off after starting up the vehicle 3 times or could go off for other reasons.
P0420 was very common where I used to live in Mexico City, largely because of the gas, but could also occur due to poor combustion caused by hot air devoid of oxygen (of which living at that high altitude was to the tune of 25% less oxygen).
What you probably got was a temporary sensor issue due to poor combustion rather than a bad O2 sensor or cat.
However, once the light goes on, the pending code will still stay there.
Generally, if the situation has resolved itself, where no more pending issues, the light will go off after starting up the vehicle 3 times or could go off for other reasons.
P0420 was very common where I used to live in Mexico City, largely because of the gas, but could also occur due to poor combustion caused by hot air devoid of oxygen (of which living at that high altitude was to the tune of 25% less oxygen).
What you probably got was a temporary sensor issue due to poor combustion rather than a bad O2 sensor or cat.
if the light were still on would an ECU reset be sufficient to solve the issue in most cases? thanks for the quick reply
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