The check engine light on my 2004 Toyota Tundra came on a couple of weeks ago. I got out my OBD II code reader to see what the problem was. It reported P0420 Catalyst System Efficiency Below Threshold Bank 1.
The root cause of that code is either my catalytic converter is not doing its job effectively or the system doesn’t think it is doing its job effectively. A catalytic converter is going to have two oxygen sensors to detect if it is functioning properly. The one before the catalytic converter is referred to as “upstream” and the one after is referred to as “downstream.”
My truck actually has two catalytic converters. The “Bank 1” means the one with the issue is the one serving the side of the engine with Cylinder #1. In my case that is the driver’s side. Check your maintenance manual for the specifics in regard to your vehicle.
Since the code indicated the issue was with “Bank 1” rather than a particular sensor, I thought it would be best to replace both. I was able get them from RockAuto.com for just under $95.
They weren’t too hard to get to. Nothing like when I replaced an oxygen sensor on my 2005 Honda Pilot and had to use a mirror to even see it.
The upstream sensor is the type the screws directly in. If you have a special oxygen sensor socket it will make things a whole lot easier. The downstream sensor slides in and attaches with two nuts. One of the nuts was completely rusted away and there was not much left of the other one. I took the little bit that was left and took it to my local hardware store to make sure I got the right size of replacement nuts.
I always like to compare the old and the new parts to see if they are the correct size, if the wire is long enough, if the plug type is the same, etc. The new sensor came with some anti-seize lubricant to put on threads so it hopefully comes out easily whenever the time may come.
I have driven my truck for just one day and the check engine light has not come back on. Before replacing the sensors, when I would clear the code it would come back within 10 minutes. This job took me about 90 minutes. I could have probably done it in 60 minutes if I would have skipped taking photos, but then you would not be able to enjoy them.