Replace both O2 sensors ?

I have a 2002 Tacoma with 220,000 miles. Im getting ready to order some parts and one of those parts is a downstream O2 sensor and on the web site when I click on the item I see this printed next to the O2 sensor as a recommendation...
Manufacturers recommend replacing O2 sensors in pairs (both Upstream or both Downstream). An older, slower sensor can cause an imbalance in the engine management system, leading to poor fuel economy and possible damage to the catalytic converter.
The Denso upstream is 110.00 and I didnt want to replace it right now. Im replacing the downstream from convenience because Im going to be replacing the muffler assy that retains it.
Any thoughts on the recommendation of replacing both O2 sensors ?
Could I cause damage ?

 

Sounds great.
Thanks for the help.
Im going to go place my order now.

 

I have a 2002 Tacoma V6 and will be replacing the downstream o2 sensor. I cut off the guard and noticed the gasket on this sensor was almost completely gone. I had just changed the upstream and still had the gasket from it that was in pretty decent shape. The nuts on the downstream were also pretty much gone and in cutting off these nuts I stripped one of the studs. Are the studs welded on or are they threaded and can be replaced?

 

They should be threaded but depending on the mileage and where the truck lives getting it out might be a project

lots of penetrating oil and maybe heat to break it loose.

For me It is just faster to weld on a new bung new studs because the studs tend to snap off

 

Wyoming09 2 dealerships tell me they're welded. I don't want to soak and heat and then find out they're welded. Anyone else know for sure?

 

Wait, what are you doing?
The studs shouldn't come out. The nuts do get pretty seized, and might even strip the stud, but worst comes to worst you just re-thread it.
The new O2 sensors come with gaskets and install flush to the old plate. No welding required.

To the original question:
The only time I'd consider replacing both is if you're going non-OEM. Even then you'll be fine as long as no CEL. If you do have a code, its not always a sensor thing. Your cat could actually be bad (as mine was), especially at 200k+.
I have non-OEM, and they've been fine for 3 years. My aftermarket AFR gauge confirms they're reasonably accurate.

 

I guess it comes down to if your truck has Toyota Exhaust installed

I have never seen any of that vintage with original exhaust

then that might be why they snap from the heat effected zone thermal cycling

 

I have replaced the muffler/tailpipe with a walker system. This setup doesn't have the complete setup as OEM which connected to 2nd cat. So the pipe from the second cat to the Walker is the OEM. I just cut it off and welded it to the Walker muffler. So yes the pipe which has the bung for the downstream O2 sensor is OEM.

 

P0420 is a catalyst efficiency code. There is an O2 code but it has to do with either the heater or unexpected signal

 

What's the code?
It's not that expensive to get a new cat put in.

 

Cat can be had for $100, weld-in for $50. I'd find a new mechanic.

 

If you can answer mine. Find out the code.

I don't remember what mine threw. It's been like 5 years.

 

So, do you want to just keep throwing in more O2 sensors or do you want to be proactive in diagnosing your problem? You're here because your mechanic has failed and you want to hear a second opinion, but we don't have your truck to play with.
If you've replaced the sensor twice and the issue hasn't moved, obviously it's time to try something else. The next reasonable thing to do is replace the thing the downstream O2 sensor is supposed to be monitoring, the cat. Other possible issues can be wiring is frayed or ECU is dying - both exponentially more unlikely.

 

It should be pretty easy to get the code from your mechanic. Or take your truck in to any auto parts store and they'll pull the code for you.

If the problem is that the cat converter is failing, aka P0420 code, then throwing new O2 sensors at is a complete waste of money.

IF the code is o2 sensor related specifically (P0135/P0136 I believe) then new front/rear sensors should do the trick.

I have a feeling you have a P0420 code and your mechanic is trying to fix it with new sensors, like a lot of people do because most don't want to admit that they need new cat converters. Cats are expensive right now, if you need 50 state legal ones anyway. If you don't, then they can be had for fairly cheap. But probably won't last long. OEM ones cost an arm and a leg because they have a lot more of the materials in them that makes them so pricey.

 

Pretty sure NY is a CARB state now, he'll need one of the expensive ones to pass emissions.

 

I've had great luck with my Magnaflow, for the record. That's what I got 5 years ago when I had the issue. I literally got 2 sensors also, then decided it must be the cat. Magically, the code that said it was the cat was the cat.

 

Yeah I have 2 Magnaflows installed too about 5 years ago, when I had a P0420 that wouldn't go away. They've held up great but I'm starting to suspect they may not have much life left in them, this last time I needed to get smogged it took over 1,200 miles for my catalyst monitors to finally set after a battery swap. Hoping it was just a fluke