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Jan 13, 2008 | 03:58 AM

Melchiah

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From: Phoenix

Bad Cat

i have a 4 banger not a truck or a ford for that matter but most engine systems are very close to being the same so i pulled a p0421 code off of my car and its is very intermittent the code only comes on when the idle gets rough and then goes away for a few hundred miles the idle gets rough like the egr is stickin. so my question is can a stickin egr cause a p0421 engine code

Jan 13, 2008 | 02:48 PM

kens64

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From: Rio Rancho USA

P0421= Bank 1 Warm Up Catalyst Below Efficiency.

Check wiring and 02 sensors. Reset PCM to see if the code comes back. Test the 02s FIRST brfore replacing cats.

What kind of vehicle?

Jan 13, 2008 | 03:49 PM

Bear River

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From: Salt Lake City, Utah

Don't just test the O2s, check the fuel trim. The trim is shown as a percentage. It should be less than 5%, ideally less than 2%. If the fuel trims are not near zero, there is a fuel management problem that much be resolved before replacing the cat. It is possible that the cat may begin working again if the condition is corrected. Fix the cause first.

Jan 14, 2008 | 01:36 AM

Melchiah

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From: Phoenix

its actually a hyundai i bought second hand i replaced o2 sensors both pre and post cat cause it had some miles and the wires looked bad on the post cat o2 i am led to believe that it is something other than the cat though due to the fact that it is intermittent how it comes and goes

Jan 16, 2008 | 08:23 AM

Bear River

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What year Hyundai?

Jan 17, 2008 | 03:45 AM

Melchiah

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From: Phoenix

its an 03 2.4/auto with cali emissions

Jan 17, 2008 | 06:14 PM

Melchiah

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From: Phoenix

i gave it a seafoam treatment a few days ago i know its not a fix but more of a maintenance item and i reset the computer and WOW it made a huge diff oh and i drove it 300 miles and no MIL/CEL came on. i feel as though perhaps i should use it more as a maintenance item every other oil change or every other other oil change