Hello everyone,

I am getting a p0420 code on my 2002 Buick Lasabre. The cat. is 4 yrs old, the front sensor is 2 or 3 yrs old. The rear sensor is original. I am wondering if it would make sense to replace rear sensor and hope it takes care of problem or go through the trouble and expense of having the system checked. at garage.

I haven't noticed any symptoms. Any advice appreciated.

You can go Autozone, and they can plot data on their scan tool, for the front and rear O2 sensors...if the rear, mirrors the front, need a cat...the front should be rapidly changing while the rear should be very slow in comparison.....if the rear mirrors, or changes rapidly like the pre O2 sensor, need a cat...

Thanks for the info Tech II. I was not aware that Autozone could do that kind of scan.

For 30 bucks you could try an O2 simulator. Just do a Google search for O2 simulator. I used the stainless steel adaptor from Big Daddies Garage. my 420 code never came back!!!! It moves the tip of your oxygen sensor out of the direct stream of exhaust so that your PCM now thinks that your cat is doing its job.