Strange Trouble code

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  #1  
Old 06-10-06, 07:19 AM
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Strange Trouble code

I have a 2001 Mazda 626 4 cyl. auto 73K. Check engine light came on. code showed PO421. "Warm up catalyst efficiency for bank 1 below threshold for engine operating conditions. " Where do I go from here. Autozone suggested changing thermostat, but not a convincing opinion. Should I start there with the thermostat ?? Any suggestions would help. Thanks
Bill from Ohio
 
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Old 06-10-06, 09:34 AM
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Location: USA
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Originally Posted by irish81449
I have a 2001 Mazda 626 4 cyl. auto 73K. Check engine light came on. code showed PO421. "Warm up catalyst efficiency for bank 1 below threshold for engine operating conditions. " Where do I go from here. Autozone suggested changing thermostat, but not a convincing opinion. Should I start there with the thermostat ?? Any suggestions would help. Thanks
Bill from Ohio
For your specific car I got a PO421 code definition of "Auxiliary Emission Controls", the definition Autozone gave you is the more general OBDII version. I'd start by clearing the code and seeing if it returns. If it comes back, then a call to a local Toyota dealer might help. I'd start with the EGR valve and see if all the connections (vacuum and/or electrical) are in good shape.

It's possible the EGR valve or something related to it has gone bad and set the code. It could be a simple as a bad temperature, pressure or other sensor. Perhaps your O2 sensors are acting up, they have a lot to do with catalytic efficiency. They are a maintainance item and should be replaced periodically.

Christopher
 
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