2002 Kia Sedona

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#1
Recently I had my check engine light come on. The diagnostic code was "PO421 01/02." When I checked this sites tech codes, there was only PO420 and PO422. Does anyone know what this could mean or if the 420 code is the same? If not, can someone tell me what this code is and let me know what I could do to fix it. I am getting ready put the van up for sale this weekend and I want to make sure it is all set and ready to go.

Thanks.
John
 

Dave

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#2
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.
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.

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

The simplest thing to do is to reset the code and see if it comes back.

Next step is to measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). The voltage should be low and steady (~200mV, depends on the vehicle). If the voltage varies (e.g. 100mV to 600mV) then it's time to replace the catalytic converter. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

hope this helps some.