what exactly is code p0421

2003 DODGE TRUCK
100,000 MILES
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BEAUTIFULHAZLEYES
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this morning my check engine light came on and its reading p0421 warm up catalyst below threshold bank 1. What exactly is this? What does it mean? How can i fix it? Thank you.
Jan 3, 2012 at 7:15 PM
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HMAC300
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it means your catalytic converter isn't getting hot enough. You'll hav eto check to make sure both of your O2 sensors are working correctly and not water leaks or air leaks in exaust system. the only way to check the O2 is with a pro type scanner.so a pro wil have to make adiagnosis on it.
Jan 3, 2012 at 9:48 PM