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Well my check engine light came on and i hooked up the reader and it came up with Code 420. Catalist system below threshold Bank 1. So is my cat bad or my O2 sensor going out. Thanks Travis :confused:
 

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TJGRCD said:
Well my check engine light came on and i hooked up the reader and it came up with Code 420. Catalist system below threshold Bank 1. So is my cat bad or my O2 sensor going out. Thanks Travis :confused:
This is normally the cat that is bad. The O2 sensors trip different codes when they fail. Do you have a V6 or I4?
 

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mine comes on so often

that at first i thought it might be the cats but they wanted 800 smackers to replace(400 rebuilt?). so first i bought the scan gauge that can read / clear and tell some of the conditions that lead to the engine light comming on. on my truck it has only come on when going under 30 mph with low rpm's, so i don't know if thats the cats or maybe dirty injectors or what. dont want to spend the 800 if it's not truly the cats. i'm not sure what you get for 800 either- both cats and both sensors-if so mybe 800 is kind of ok. anyway the lite come on only about once a week so i want to do the seafoam thing first, plus i don't need to smog for another year and a half.

ps-150000 miles on mine
 

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Discussion Starter #4
well i got an I4. It has came on twice now. Once while driving in the snow up in the mountains. And then once again coming down out of the mountains. Both times cruising down the freeway.
 

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TJGRCD said:
Well my check engine light came on and i hooked up the reader and it came up with Code 420. Catalist system below threshold Bank 1. So is my cat bad or my O2 sensor going out. Thanks Travis :confused:
P0420 is tripped by the comparison of both 02 sensors. It could be the cat or just your engine a/f ratio out of whack. Some of the minor problems that can trip the code would surprise you.

Code P0420 indicates that the exhaust gas exiting the catalytic converter is too similar to the exhaust gas entering the converter. A faulty or overloaded converter due to an unbalanced air/fuel mixture can cause this condition.

Check the exhaust system for air leaks or holes rusted through. Any outside air that leaks into the exhaust can go through the cat as lean exhaust and hurt its efficiency.

Rap on the converter with a fist or a soft mallet and listen for anything loose or rattling inside. If the catalyst element is cracked or broken apart then the cat will need replaced.

You may want to test the O2 sensors for proper operation. Because these sensors tell the computer about the performance of the converter, malfunctioning O2 sensors can set this code. Verify that the sensors are faulty before replacing.

There may be another problem causing the engine to burn an excessively rich or lean air/fuel mixture. This could overload the cat and ruin its efficiency as well.

Common causes include incorrect fuel pressure, an EGR system malfunction, an MAF sensor malfunction, intake or vacuum leaks, incorrect cam timing, a bad PCV system, misfires, injector problems, cooling system problems, a restricted air filter, a head gasket leak, or a high oil level.

From: http://actron.com/faq_detail.php?pid=16154&id=13
 

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did you figure it out yet or did you just erase the code?
 
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