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P0420 Catalyst System Efficiency Below Threshold - 2000 Chevy Prizm (Toyota Corolla Equivalent) Diagnosis & Repair Guide

Model: Prizm Fault Code: P0420 Posted: 2009-03-06 22:34

My Check Engine light has come on recently, within the past two months. After checking at AutoZone, I was given diagnostic code P0420: Catalyst System Efficiency Below Threshold (Bank 1). I own a 2000 Chevrolet Prizm, which is nearly identical to the Toyota Corolla in design and engine setup. I'm trying to determine whether this issue requires replacing the entire catalytic converter or just the oxygen sensors. How can I test the oxygen sensors myself? What type of catalytic converter should I look for (e.g., similar to https://cgi.ebay.com/ebaymotors/MAGNAFLO)? The check engine light has triggered multiple times, only to turn off after a day or two and reappear later. Does this pattern suggest a sensor issue or a failing catalytic converter? If the problem is indeed with the catalytic converter (not the sensors), what would be a reasonable cost for replacement? Is it possible to perform this repair myself? Any insights or recommendations would be greatly appreciated!

Related fault codes
P0420
Comments (3)
Anonymous 2009-03-08 07:02

P0420 is typically caused by a failing catalytic converter, occurring in about 98% of cases. Make sure to install a high-quality converter—cheaper models often fail prematurely. Original Equipment (OE) parts are recommended for reliability. Note: You didn’t mention the vehicle’s mileage. Check with your Chevrolet dealership regarding warranty coverage. Most catalytic converters come with an 80,000-mile warranty.

Anonymous 2009-03-08 12:19

The vehicle is around 75,000 miles. I purchased it used from a friend who drove most of the mileage on it, but he originally bought it at under 10,000 miles. How can I verify if there's still an active warranty on the catalytic converter? Also, what does 'OE' mean—is it a brand or a specific type of part?

Anonymous 2009-03-09 07:00

Contact your local Chevrolet dealership and ask about their catalytic converter warranty policy. Since this is an emissions component, the warranty typically covers the full term regardless of vehicle ownership changes. 'OE' stands for Original Equipment—meaning it's a part manufactured by the same company that originally equipped the vehicle (e.g., GM). Many aftermarket converters cut corners on precious metals needed for efficient catalytic function, which leads to early failure and repeated replacements.