p0420 code help

[nissanpark1]

My 2000 nissan sentra GXE "service engine soon" light turned on in january(69720 mile). I checked it up by dealer. They told me some o2 sensor was wrong.

here is the report.P0420 Tw catalyst system B2. Catalytic convertor function failure.Front and rear o2 sensors for B1. Rear o2 sensor b1 response is like front o2 sensor b1 reading. No function through catalytic convertor. Correction on cause system is bank1 not bank 2.

can anyone help me figure out which sensor is wrong and how to replace it?

thanks

[nametakennow]

What that says is that your precat isn't functioning. However, the code can also come up if the 2nd O2 sensor isn't functioning.

Unfortunately, it could be either. The sensor is cheaper to replace, so I'd go that route first.

If you wanted to test to be sure, you could check the voltage on the second sensor wires against manufacturer's spec, which is in the FSM (link in my signature). To check the precat, take off the manifold and shake it. If it sounds like there's gravel bouncing around inside, your precat has broken up.

Welcome to NICO!

[nissanpark1]

I went to the send dealer, they said it is Catalytic convertor failure, it is still under warranty, they replaced it for free. it was covered for 8 years and 80000 miles nationly.so the first dealer tried to rip me off.

[nametakennow]

Some dealers try to avoid doing work like that, good thing you found one willing to fix it.