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  • colin_l 07/21/09 5:12 pm PST

    P0420 can be a bear, but thanks for a good question with some helpful details.

    If you are setting this code at idle, it's 'better' than while driving.

    Step 1 is to pull the battery for an hour, and tap the brake before hooking the ECU back up. This should ensure a soft reset and clear the code. A full reset would require an OBDII scan tool, which you might not have access to.

    If the code sets again, but still at idle, I would consider replacing the catalytic converter(s). If you have a lot of miles on the truck, they could well be ineffective or clogged. If you have exhaust leaks like a cracked header, it can also cause P0420.

    Everyone seems to jump straight to replacing the o2 sensors, but I'd start with the above.

    Source: http://www.p0420.com/

  • colin_l 07/21/09 6:09 pm PST

    Sorry, thought of something else.

    The 4.3L was in use a very long time. You can probably find low mileage cats in salvage yards for a lot less than new ones. Call around, and compare this against quotes from local exhaust shops. (BTW if you do go to an exhaust shop, I suggest a large local shop instead of a chain. The locals usually have tremendous skill with torches and benders that is severely lacking at your average national chain store. Sometimes they charge a lot less, too!)

  • autoinquirer 11/01/11 7:15 am PST

    I have the same Code with my Chevy Blazer. I want to ask you how many Oxigen sensors have this car? I changed two. One by the catalyst and one close to the motor. A friend told me that the car have three sensors close to the motor, thrue? Also, I just changed the catalyst a little more than a year ago and they gave me only one year of warranty. Should a Catalyst last at least more than a year or it is because they did a terrible job? or the truck is just too full of miles that brakes catalysts?

    Thank you for your help!

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