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From the Actron OBD II website:
"P0420, P0430 Catalyst Efficiency
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."

Clean the Maf sensor first (it's the cheapest thing).
Spraying carb cleaner around vacuum lines will show any leaks.
Dont know how much troubleshooting you've done on this problem but in the long term your better off checking the simple items to eliminate them. I've found the MAF sensor on these trucks causes the majority of related CEL's.


279 Posts
That doesn't sound like the symptoms of a bad catalytic converter. I'd pay the $70 and have it checked out unless you have a real diagnostic computer that allows you to look at the signals from the sensors used during closed loop.

The little code scanner isn't going to help in this case except to tell you what you already know. At best you might change a few sensors before you get it right.

jimmytbud7 said:
i run 93 octane in my 2000 v6 constantly to keep a check engine light from coming this bad?
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