P0420 is almost always a bad cat. You can check your o2 sensors with a scan tool and they should "toggle". On average, the front o2 sensor will toggle between roughly 100 to 800 hertz. The rear will toggle far less say.... 100-300 hertz. If your cat is working properly that is. If your cat in inefficient, your rear o2 sensor will nearly match your front o2 sensor, indicating no change, or that your cat is not working properly. You can also take a temperature reading of the cat. There should be roughly a 50 degree difference between the inlet and outlet temperature of the cat.

On the whole, before replacing your cat, make sure your engine doesn't have any other driveability/runability problems. Make sure your engine goes into closed loop, isn't running rich, etc, etc. If all that check out, 9 times out of 10 it's a bad cat.

-Wrench

 

The wire coming off mine was resting on the hot muffler and caused mine to go on and off, Just something to check on.

 

hey all, just wondering, 8 years or 80k miles? i have a 97 with 120k on it, i'm under 8 years, but what about the 80k? kind of don't understand this concept of warranty, any help, i know i'm a buffoon, it's all the altitude here in tahoe. -dd

 

Whichever is less. Think of it as "Less than eight years AND less than 80k miles". If you go over either limit, the coverage expires.

 

Always remember the warranty terms will favor them not you and it is pretty easy to figure out the coverage.

 

thanks guys, my code was p0133 - o2 sensor ckt, slow response (bank 1 sensor 1). so...luckily i believe it's my front o2 sensor bank, will replace soon. thanks for all the help, dd

 

Bank 1, sensor 1 will be the sensor before the cat.