Oxygen Sensors: Can they be saved?

The Check Engine light in my 2005 Toyota Tacoma V6 came on today. It indicates "O2 Sensor: Bank 1, Sensor 1".

First question: Can anybody confirm which side is Bank 1? My guess would be driver's side, but I want to be certain.

Next: The sensor is almost $200 from Advance. I can't imagine what it would be at the dealer. I've had to deal with surprisingly few O2 sensors in my life. How do they fail? Is it an internal problem? Bad wires? Or just dirt and corrosion? Is it possible to just clean and reinstall?

Bank 1 is always the side that cylinder #1 is on.

Most of the time, #1 is the front passenger side on RWD V engines.

How do they fail... well, most of the time the heater dies- or usually it breaks. If that happens, you are SOL, and have to replace it. For circuit issues, there's a MIL light specifically for that- open, short, whatever- it would be a different code.

But many O2 sensor codes are the result of other problems.

Unless you found leaded gas, it's quite unlikely that it's dirty and can be cleanded.

That was quick and informative. Thank you.

Toyota's really good about O2 diagnostics. If the PCM says it's bad, then it's almost certain to actually be bad.

O2s do wear out and/or drift over time. Newer PCMs actually calibrate the front O2 off of the rear O2 during the period before the cat lights off. Theory is that the rear O2 lasts longer because it sees less heat. The sensors can have noticeable drift in as little as 25k miles, so really, I'd just replace it first and ask questions later.

The only gotcha is if there is an exhaust leak upstream of an O2, which introduces oxygen and fakes the sensor lean. Oftentimes it will be enough to throw a lean code, O2 not switching code, or catalyst inefficiency code if the leak is upstream of the rear sensor.

Now, the fun part - there's a strong possibility that your truck uses a wideband. You'll know it if the thing costs $250 instead of $100. Toyota has four-wire wideband sensors. The only way to know for sure is to read the datastream.

Like Knurled said. The are an air/fuel ratio sensor, and there sin't really any way to check them, let alone fix them, so trust the code.

Also, I have found that this is a poor place to try saving money. OE Toyota, or NGK I would trust. Anything less than 1/2 price is probably the wrong part.

Knurled wrote: Toyota's really good about O2 diagnostics. If the PCM says it's bad, then it's almost certain to actually be bad. O2s do wear out and/or drift over time. Newer PCMs actually calibrate the front O2 off of the rear O2 during the period before the cat lights off. Theory is that the rear O2 lasts longer because it sees less heat. The sensors can have noticeable drift in as little as 25k miles, so really, I'd just replace it first and ask questions later.

They shouldn't drift so much in 25k that it matters- the system is supposed to last for 120k miles for a Federal cert or 150k for a CARB cert with no changing parts.

Oh, and one can use the rear sensor to center the front even when the catalyst is warm. Particularly with a WB- while they are quite good at a/f control, they are not as accurate at stoich as normal O2 sensors are. Not that it's fully how they are used, but that's the general why. No real need to do it on a NB front O2, since they only really get lazy...

Good call on the possible WB- they have been in Toyotas for longer than many, and I know we had WB in production vehicles in '06. That's a big reason why they would be that expensive.

Streetwiseguy wrote: Like Knurled said. The are an air/fuel ratio sensor, and there sin't really any way to check them, let alone fix them, so trust the code. Also, I have found that this is a poor place to try saving money. OE Toyota, or NGK I would trust. Anything less than 1/2 price is probably the wrong part.

The only commercial producers of WB sensors are NTK and Bosch. Denso and Delphi want to, but it will be a while. And for a Toyota, I'm leaning toward NTK.

alfadriver wrote: Bank 1 is always the side that cylinder #1 is on. Most of the time, #1 is the front passenger side on RWD V engines.

unless it's a GM.. or a Dodge..

I believe that long term use of cheap gas can shorten their life. Friend of mine burns the cheapest crap he can find and replaces sensors every 50k or so. (of course he blames the cars) I burn good gas and have only changed one years and years ago on a used car.

I think cheap fuel is parallel, not a cause. Did you know that Big Lots sells API SB rated oil for $2/quart? Not SJ or SL or SM or SN but SB. Some gas stations sell it, too.

Or how about how it's cheaper to go through a gallon of coolant every thousand miles than it is to fix that weepy intake gasket?

Little things like that add up.

For what it's worth, I run cheap fuel almost exclusively and I've never had an O2 failure, including the Bosch wideband that came with my LC-1. (I am not going to count "smashed by a rock" as a failure )

Knurled wrote: Did you know that Big Lots sells API SB rated oil for $2/quart? Not SJ or SL or SM or SN but SB.

Really??? That's, like, 1975 quality. How does that work? Drain the oil out of a diesel truck, strain it through the wife's pantyhose and bottle it?

Gearheadotaku wrote: I believe that long term use of cheap gas can shorten their life. Friend of mine burns the cheapest crap he can find and replaces sensors every 50k or so. (of course he blames the cars) I burn good gas and have only changed one years and years ago on a used car.

I don't doubt this.

Two tanks of reputable brand gas in the NC, and it's registering much better mileage even with E10.

Gearheadotaku wrote: I believe that long term use of cheap gas can shorten their life. Friend of mine burns the cheapest crap he can find and replaces sensors every 50k or so. (of course he blames the cars) I burn good gas and have only changed one years and years ago on a used car.

I don't doubt this.

Two tanks of reputable brand gas in the NC, and it's registering much better mileage even with E10.

Knurled wrote: I think cheap fuel is parallel, not a cause. Did you know that Big Lots sells API SB rated oil for $2/quart? Not SJ or SL or SM or SN but SB. Some gas stations sell it, too. Or how about how it's cheaper to go through a gallon of coolant every thousand miles than it is to fix that weepy intake gasket? Little things like that add up. For what it's worth, I run cheap fuel almost exclusively and I've never had an O2 failure, including the Bosch wideband that came with my LC-1. (I am not going to count "smashed by a rock" as a failure )

Wal Mart carries Accel SA rated 30W oil...

Knurled wrote: Toyota's really good about O2 diagnostics. If the PCM says it's bad, then it's almost certain to actually be bad. O2s do wear out and/or drift over time. Newer PCMs actually calibrate the front O2 off of the rear O2 during the period before the cat lights off. Theory is that the rear O2 lasts longer because it sees less heat. [snip]

Maybe I'm wrong, but my understanding is the front 02 sensor sees a lot of heat because it's in front of the catalyst, and the catalyst must heat to a certain temperature to begin operation. So it's in a fairly hot area of the exhaust gas.

But once that happens the exhaust temperature behind the cat is higher, since the catalyst is generating its own high, stable temperature; higher than the exhaust gas in front of it.

At least that's how I understand it to work.

Johnny2Bad wrote:

Knurled wrote: Toyota's really good about O2 diagnostics. If the PCM says it's bad, then it's almost certain to actually be bad. O2s do wear out and/or drift over time. Newer PCMs actually calibrate the front O2 off of the rear O2 during the period before the cat lights off. Theory is that the rear O2 lasts longer because it sees less heat. [snip]

Maybe I'm wrong, but my understanding is the front 02 sensor sees a lot of heat because it's in front of the catalyst, and the catalyst must heat to a certain temperature to begin operation. So it's in a fairly hot area of the exhaust gas. But once that happens the exhaust temperature behind the cat is higher, since the catalyst is generating its own high, stable temperature; higher than the exhaust gas in front of it. At least that's how I understand it to work.

Partiallty correct. The front O2 sensor does see a lot more heat. The first O2 sensor is usually the limiter of exhaust temps- so when it starts to become a problem, the engine will run richer to keep it's tip temp cool enough to be durable. Front (main) catalyst temps are hotter, but they are more durable.... I could go on, but that is the hot area.

For the second O2 sensor- it never gets that hot- even with the catalyst raising the temp, either by packaging or just by heat loss- it never gets as hot as the front one. To the point where a non intelligent heater can be used, since it's normally never at risk of overtemping.

So, in summary, inlet temp is lower than cat temp, exit temp is most of the time cooler than mid brick temp, but second O2 isn't very hot.

novaderrik wrote:

alfadriver wrote: Bank 1 is always the side that cylinder #1 is on. Most of the time, #1 is the front passenger side on RWD V engines.

unless it's a GM.. or a Dodge..

Well, then look at the book to determine which #1 is. That's always bank 1.

What is it indicating? I'm sure lean or fat.

Streetwiseguy wrote:

Knurled wrote: Did you know that Big Lots sells API SB rated oil for $2/quart? Not SJ or SL or SM or SN but SB.

Really??? That's, like, 1975 quality. How does that work? Drain the oil out of a diesel truck, strain it through the wife's pantyhose and bottle it?

the dollar store in my 'hood sells API SA! I took a picture of the label because I was so shocked to see it.

Noob question- so what are the ramifications if a certain hypothetical individual ignored the bad O2 sensor warning? Like for a really long time?

Jerry wrote: Noob question- so what are the ramifications if a certain hypothetical individual ignored the bad O2 sensor warning? Like for a really long time?

Many states use the MIL light as an inspection pass/fail. If yours doesn't....

Besides your emissions not being all that great (MIL light triggers at 1.5x the certified standard), what you will probably notice is a change in fuel economy, and depending on the OEM, they also may take action to make sure other things don't get damaged by the bad sensor- like run a little richer, perhaps a little less agressive spark, etc.

If the MIL starts to flash, then you are getting a misfire, which can cause the catalyst to suddenly over temp. But I doubt you'll get that far.

A fuel economy drop off will be the biggest issue, I suspect.

Partsgeek says it's a $52 problem - which is more inline with what I'm accustomed to be paying for BMW O2s.

http://www.partsgeek.com/gbproducts/DC/18535-05169344.html?utm_source=google&utm_medium=ff&utm_content=DN&utm_campaign=PartsGeek+Google+Base&utm_term=2005-2006+Toyota+Tacoma+Oxygen+Sensor+Denso+Downstream+Left+05-06+Toyota+Oxygen+Sensor&gclid=CI25xKW66LYCFYHe4AodmWEASg

My wifes mazda 6 had a BAD surging problem when her O2 sensor failed.

The surge was there at idle, partial throttle, even WOT.

This seemed strange to me because I didn't think the sensor was always being used. The car was throwing a code for the IAT sensor. WE replaced teh IAT and it didn't fix the problem.

For E36 M3s and giggles, we unplugged the front O2 sensor. Problem went away. We got a new one and installed it. Problem is gone!

I guess what I am saying is that there can be some other issues with ignoring a bad O2 sensor.

Rob R.

In reply to Giant Purple Snorklewacker:

Isn't he looking for the upstream one?

Giant Purple Snorklewacker wrote: Partsgeek says it's a $52 problem - which is more inline with what I'm accustomed to be paying for BMW O2s. http://www.partsgeek.com/gbproducts/DC/18535-05169344.html?utm_source=google&utm_medium=ff&utm_content=DN&utm_campaign=PartsGeek+Google+Base&utm_term=2005-2006+Toyota+Tacoma+Oxygen+Sensor+Denso+Downstream+Left+05-06+Toyota+Oxygen+Sensor&gclid=CI25xKW66LYCFYHe4AodmWEASg

And an easy fix, so go get your gloves on and maybe a soldering iron. You'll be better off for it.