Q replacing O2 sensors. (Replace both?)
 

So I pulled a P0133 today on the way home from work. Had the code cleared and it hasn't reappeared since. All my reading leads me to believe that the O2 sensor needs to be replaced. I figure I'll go ahead and clean the MAF while I'm at it.

I haven't been able to confirm it, but my reading leads me to believe that there are two O2 sensors. Is this true? If I'm to replace one, should I go ahead and replace both?

More than likely, yes. There should be one before the catalytic converter(s), but after the crossover and the other should be after the catalytic converter(s).

I would.

i would do both while your under there just soak the bolts with pb blaster for a few hours

I remember reading somewhere that one of them is a lot more likely to go out than the other, and that you might as well just replace the one that goes out. It would be a while till the other one, less susceptable to fail, would go out. Not sure how true this is, but lets see if somebody can confirm it.

Yes, there is one in front of the cat and one behind it. The front one is there to read the A/F mixture and report the data to the ECU which then adjusts the fuel mixture to get to "Stoich" which is the "optimum" A/FR (Air/Fuel Ratio) of 14.7:1.

The one behind the cat is there to be sure that the cat is doing it's job. It has no bearing on how the engine is running.

Did you happen to search on "P0133". There is a ton of discussion about this.

Anyway... The P0133 is:This means that the ECU doesn't think that the FRONT O2 sensor is providing data in a timely manor. That's a sign of it getting old.

There is NO reason to replace both sensors. Even from a "preventative maintenance" point of view. The rear sensor will run you about $90, the front one for your year is about $130 (I think). Replace the rear one when the ECU complains about it, nothing will happen to the driveability of the truck when it goes, whereas the front one being flaky will turn into poor mileage and/or power.

Thanks for clearing that up for me, guys.

And yes, Mark, I read every single post in every single thread last night that contained "P0133" :baby: I just got the feeling that there was more than one, and was curious if it was a good idea, preventative-maintenance-wise to replace both at the same time.

I can pickup an Denso O2 sensor from a local auto parts shop for $141. Or order one from Gadget (urdparts.com) for $8X. I think I'll hold out a while longer and see if I get the check-engine light again soon.

I need to purchase some minor parts from Toyota anyway. Need to replace the clutch spring bushing-thingy (squeeeeeking) and the gasget above the gear box so it shifts a bit easier.

Mark is right on, except....
If it is a 1998 then both sensors should be an O2 sensor and both should be about $90 from URD.
Only replace the front sensor as Mark suggested.

Thanks Jamie... I never remember where that cutoff point is!

Popped another code on the way home.

Order placed 2 day from URD. Hopefully mine will survive until Friday.

I want my truck to shift easier, can you point me to some info on this? I'll do a search, but just in case you got something else...

Sure...

It appears from what I've seen and read that the front O2 sensor takes the brunt of failures. I had the one ahead of the cat replaced and figured I'll wait for the one behind to go in lieu of doing both, especially since the later doesn't impact driveability like the 1st one might (my truck actually got better mileage with the bad sensor!). Matter of choice, I suppose.

It's in hotter gasses, and the ECU is looking for a lot more to go out of kilter than the rear.


Sounds like the front one was reporting rich, which forced the ECU to run things lean, which isn't always good.

"Driveavbility" doesn't just mean "good mileage". Acceleration, torque, engine life... there's a lot of stuff in there.

Just to add to that.....there are also alot of particulates/unburned hydrocarbons in those exhaust gasses which can deposit/accumulate on the front sensor over time, while the rear sensor stays quite shielded from this effect since the vast majority of these particulates/HCs are burned off in the catalytic converter at very high temps thus it still accumulates, just MUCH slower.