They said to me that its too big CO three times bigger than it should be.

Reading a lot about the AFR/O2 sensor (upstream) replacement before I dive into it. Thought I’d summarize the main points below, and maybe someone can advise if I’m missing anything

Tools:
-wrench/socket wrench/vice grips
-wd-40


Basic tips seem to include:
-spray with wd-40/penetrator first
-disconnect negative battery terminal
-unbolt sensor before unplugging
-use new bolts (2?) when installing the new sensor.

Any other tips I should be aware of?

Questions I still have:
-Where do you get the bolts and is there a part number or size I should be looking for?
-Do you recommend changing both AFR/O2 sensors at the same time? Would this help the computer/gas mileage?

Final point:
-I’ve read different views that you should remove the front wheel for easier access, but others say this isn’t necessary. I guess if it gets too difficult then the tire will come off

06 SR5 with 190k. Cali model (dual cat.s, next to the engine)

Just watched Timmy the tool mans video on this and worth the 20 minutes.
Hope it helps.
YouTube

LMS

I see you have a 2006 (unless that was a typo), but the same principle remains. You'll unplug the sensor in question and replace. However, I believe 06's have multiple upstream sensors so be sure you replace the right one and only use DENSO or genuine Toyota parts (DENSO is the OEM for oxygen or air/fuel sensors).

To answer a few questions:

-Where do you get the bolts and is there a part number or size I should be looking for? The bolts, if they are present on the 06, are welded on the exhaust. It's the nuts that are removable and can be replaced if damaged by rust or stripped. Some newer models like the 06 have screw-in sensors with no nuts or welded bolts at all.
-Do you recommend changing both AFR/O2 sensors at the same time? Would this help the computer/gas mileage? No, they get pricey. If you really want to try and restore efficiency, replace only the upstream sensor(s) before the cats since they control the majority of the fuel trims.

Final point:
-I’ve read different views that you should remove the front wheel for easier access, but others say this isn’t necessary. I guess if it gets too difficult then the tire will come off. It's up to you really. I'm a thin guy and with these high clearance 4Runners there's plenty of room to shimmy under the exhaust pipe. Just make sure it's not hot!

Thanks gamefreak for the detail.

To be clear, I was referring to replacing both AFR sensors (also known as the upstreamO2 sensors, not the O2 sensors behind the cat). I’ve seen those terms used interchangeably so thanks for clarifying. But even replacing only the two forward/upstream sensors can get pricey quick, so is it ok to just replace one (in this case replacing only the passenger side, and leaving the older driver side forward AFR sensor, at least until it starts throwing a code.

And that’s a good recommendation @Last Man Standing . I’ve had that video saved but didn’t have WiFi so haven’t been able to watch. I’ll take a look at it.

CelticRunner,

Most welcome, as I am so new to this 4Runner world I mostly read and stay on the sidelines. My takeaway on the video was he used PB blaster the night before and he thought that helped with nuts, also watch where he analyzes
the Ohm reading on the O2 connector to see if it is necessary to replace them as they are pricey buggers as he mentions. Also, note the direction of the gasket install and the fact he needed a adjustable head ratchet on one of the O2 sensors due to an obstacle on his model.

Was thinking of doing mine ( 02 ) but his results for improved mileage was only 1 MPG gain for his efforts and investment?

Regards,

LMS

Yes you can most definitely just replace the one. I think they run what, about $120 per sensor? That will at least take care of the code and allow you to drive happy.

Ok, dumb question, but how sensitive is the sensor? Is it ok to touch them? What’s the consensus?

I have always read to never touch them, but I bought it from the auto parts store and the guy took it out of the box to show me. There was no plastic covering the sensor (Denso) and the guy started handling the sensor side of the part. I questioned him regarding the sensitivity of the sensor (and not touching it) and he blew it off saying that it comes in contact with hot exaust so touching it won’t hurt.

Any thoughts? I’m hesitant to try the instal until I can confirm this won’t create an issue


Edit: the copper thread stuff is in the box, so I don’t believe it’s old. The metal is a little discolored though, as you might see when someone touches a piece of metal (oil from hands?)

I did watch the Timmy Toyota man video and saw that he lightly bumped the sensor on the pipe when inserting it, so maybe it’s not quite the issue I thought

Parts guy is right. Don't drop the thing in a tub of oil, but a little residue from your clean hands isn't going to spoil it. Best not to touch it once you start working though in case you have sealant/oil/whatever on your hands.

Okay I hope I am not hijacking this thread.

I have 2000 4Runner V6 3.4L 4X4 Limited - CALI - (2) CATS

Got a P0420 Code was going to replace the downstream O2 Sensor behind second CAT right before muffler and if that didnt work I would try replacing the A/F Sensor up front. Any suggestions?

Also, which Denso sensors (part numbers please) do I need for both?

Thanks

234-4261 (downstream)
234-9002 (upstream A/F)

Rockauto link

It's an easy job, do it yourself, use liquid wrench on the old 02 sensor, unplug, unscrew and replace.

I think you are

but you can look at this anyway
P0420 Oxygen Sensor Simulator Hack: 7 Steps

I concur. I kind of feel like if I can somehow manage it then anyone can do it. The hardest part was working in the tight area. Would have need easier if I had the pivot ratchet with torque attachment.

Instead I started it with a small wrench and a thick dowel, then tapped it loose. Ill probably rent the right tool next time, or maybe buy it if I’m in a better financial position. Haha