O2 sensors

I have recently had about $1620 worth of work done on my 2000 4Runner because the check engine light came on and the code was P0420…my invoice says they replaced the exhaust pipe assembly (about $1300 of the 1600). Now 2 weeks later the light is back on with the same code…are the 02 sensors part of the “exhaust pipe assembly” or are they now going to tell me I need a bunch (2-4) 02 sensors replaced. Would appreciate any insight as I take the car back to the dealership that did the original work.

The o2s is screwed into the exhaust pipes. Bank 1 O2 sensor refers to the side of the engine which contains cylinder #1. It could be any number of things. Here’s a link to help. http://www.p0420.com/

How many three way cats do you have? If you have two of those, then the P0420 would be for only one side, the other side will give you a P0430.

I don’t know what they are going to tell you but they should only suggest one of the second O2 sensors, and they probably weren’t included in the exhaust system. Generally you will be better off with an O2 sensor from Toyota instead of an aftermarket one, even though they cost more. A re-flash of the computer may also be recommended.

I would ask the dealer to do the re-flash for free since they already charged you so much money and their first recommendation did not work. They should also replace the O2 sensor for parts cost only.

The attached link
shows the exhaust configurations used in the 2000 4Rrunner. The catalytic converter is the first canister in the pipe with the convolutions in the casing. Unfortunately, Toyota seems to use the term “exhaust pipe” for the converter rather than “converter”, confusing conversation.

The oxygen sensors aren’t shown in he drawings but would be mounted in the unidentified mounting blocks just fore and aft of the converter.

To us it’d help to know exactly what they changed. If you can, locate the proper system based on your engine and identify the actual parts changed using the part numbers identified in the link, getting the changed numbers from your copy of the shop order.