Should I replace BOTH of my oxygen sensors? No engine codes...

[m4gician]

Hey everyone,

From the research and articles i've looked at, many people say Oxygen sensors should be replaced periodically (every 160,000km). They improve fuel economy of done, etc.

My care has two oxygen sensors. I haven't received any codes about them, or even relating to what could be an o2 sensor problem.

Should I replace either? Just one? (Which? up or down) or both?

Let me know RFD. Is the gain in fuel economy or performance worth it?

[001Stunna]

lolz dont replace em if they aint broken man, and even if u do DO NOT BUY EM LOCALLY. Can get them much cheaper online...much much cheaper.

However, if you want, pass by one day(around davenport/caledonia area) and ill read your ecu and see if they're working properly or acting lazy or w/e, plus ive been meaning to shoot you a pm regarding some detailing things if you're still doing it.

[m4gician]

lolz dont replace em if they aint broken man, and even if u do DO NOT BUY EM LOCALLY. Can get them much cheaper online...much much cheaper.

However, if you want, pass by one day(around davenport/caledonia area) and ill read your ecu and see if they're working properly or acting lazy or w/e, plus ive been meaning to shoot you a pm regarding some detailing things if you're still doing it.

Thanks for the tip man, I've always ordered my parts online, they're 50% off or better online. OEM o2 sensors are down from $240 US ($300 cad) to $100 USD. I may go with universal ones for less, but meh, OEM is plug and play.

If they won't affect performance, I won't replace them. But I need to see if RFD has a more experienced opinion than mine.

[001Stunna]

Thanks for the tip man, I've always ordered my parts online, they're 50% off or better online. OEM o2 sensors are down from $240 US ($300 cad) to $100 USD. I may go with universal ones for less, but meh, OEM is plug and play.

If they won't affect performance, I won't replace them. But I need to see if RFD has a more experienced opinion than mine.

Well your front o2 sensor is there to work with air/fuel ratio and should range from about 0.1-0.9volts. Usually if looking at a graph it usually goes 0.3-0.7v.

Your o2 in the cat is there to tell the ecu how the cat is performing and if its doing its job. Its voltage should be more stable and shouldnt have much variance.

If anything though as i said ill shoot you a pm later on tonight with some other things and if things work out and i run into you i can read your ecu and see how the o2's are performing as well and you can sort of make up your mind a little bit more if u wanna change em or not.

[corrupt123]

$100 each for new ones and you have no codes?

You'd need to drive like a billion km to make back your investment on the almost non-existent fuel savings you'd get. Don't bother.

[Pete_Coach]

Do not replace them on speculation. If they work, they work. There is no such thing as "lazy". There is no such thing as "failing". It has failed or not, period. The front O2 sensor takes a pre-read and the back one ensures your converter is working. If there is a differential, then the CEL light will come on.
No performance gain with new sensors.

[maniacshopper]

in your console, is there an error code?
If there is, get an obdII reader.
if there's problems with co, oh, NOx, you've got either a fouled O2 sensor, fouled spark plug, running air fuel mixture too lean or too rich. Or maybe EGR is clogged.

[ES_Revenge]

Do not replace them on speculation. If they work, they work. There is no such thing as "lazy". There is no such thing as "failing". It has failed or not, period. The front O2 sensor takes a pre-read and the back one ensures your converter is working. If there is a differential, then the CEL light will come on.
No performance gain with new sensors.
I tend to agree. I think the days of replacing O2 sensors after x number of miles are over. These days they can last quite a while and you'll never have a problem. I don't think you'll do any harm in changing one or both (unless you replace it with some made-in-China sensor, lol) but I don't think you need to replace it if it "ain't broke".

[Anonymouse]

Unless you get a code, I'd leave them alone. On the other hand, if you expect to keep the car for a few years, at that mileage you're going to have to replace them anyway and you may as well do it now.

[theguyz]

I disagree while the famous O2 sensor replacement was for savings on gas which was minute, a bad/faulty O2 sensor can make your car run horrible and cost more down the road for repairs caused by a bad O2 sensor.

If its not throwing codes, and your not at replacement km's i'd suggest just removing and cleaning them. They could have some carbon on them and cleaning them may increase lifetime.

[ottofly]

I disagree while the famous O2 sensor replacement was for savings on gas which was minute, a bad/faulty O2 sensor can make your car run horrible and cost more down the road for repairs caused by a bad O2 sensor.

If its not throwing codes, and your not at replacement km's i'd suggest just removing and cleaning them. They could have some carbon on them and cleaning them may increase lifetime.

I would not recommend that. Sometimes, taking an O2 sensor out and putting it back in may result in a code being thrown not to mention the risk of breaking a wire or stripping the threads. If fuel economy is stable with no suddden increase in consumption and no code is displayed, then I wouldn't touch them. My '98 civic has the original sensors and the car has 230,000km. O2 sensors can go a long way before they need replacement.

[ShadowVlican]

Do not replace them on speculation. If they work, they work. There is no such thing as "lazy". There is no such thing as "failing". It has failed or not, period. The front O2 sensor takes a pre-read and the back one ensures your converter is working. If there is a differential, then the CEL light will come on.
No performance gain with new sensors.
plenty of threads in subaru forums regarding lazy O2 sensors

[m4gician]

Thanks for all of the info guys, i wont be replacing them then. Haha. As for cleaning them, I'm told (and have read) have to clean them by heating them to burning off deposits?

[Qube]

O2 sensors should be replaced near the 160k mark depending on the car. If your car will throw a code for it then go ahead and hold off a bit. The worst case is it's dead and kills your cat converter... then you're talking big bucks. This is one of those things that could be preventative maintenance like fan belts and fuel filters.

[jetway1212]

Do not replace them on speculation. If they work, they work. There is no such thing as "lazy". There is no such thing as "failing". It has failed or not, period. The front O2 sensor takes a pre-read and the back one ensures your converter is working. If there is a differential, then the CEL light will come on.
No performance gain with new sensors.

I guess you have never tuned cars. Having a fully programmable ECU with onboard datalog is awsome, it can tell you lots of thing you dont know.

OP, when in doubt take it to a shop who can read more than error codes. Not all errors throw a CEL.

Not sure what car you're driving either.

[jetway1212]

I would not recommend that. Sometimes, taking an O2 sensor out and putting it back in may result in a code being thrown not to mention the risk of breaking a wire or stripping the threads. If fuel economy is stable with no suddden increase in consumption and no code is displayed, then I wouldn't touch them. My '98 civic has the original sensors and the car has 230,000km. O2 sensors can go a long way before they need replacement.

Depend on the cars. I know Honda OEM Densol sensors are so damn sensitive. You have to handle very carefully.

On Nissans, i have removed and cleaned the sensors plenty of time. Dont physically clean it, spray Seafoam on the tip and let it drips.

[DavidY]

Duplicate

[Pete_Coach]

plenty of threads in subaru forums regarding lazy O2 sensors
"Lazy" O2 sensors are figment of the imagination of wannabe mechanics. There is no automotive proof of this phenomenon. Well, let me back off a bit, yes, there are O2 sensors that can, for various reasons be slow to react but, without triggering a CEL, it is still within the parameters set out by the vehicle OEM.
O2 sensors should be replaced near the 160k mark depending on the car. If your car will throw a code for it then go ahead and hold off a bit. The worst case is it's dead and kills your cat converter... then you're talking big bucks. This is one of those things that could be preventative maintenance like fan belts and fuel filters.
Firstly, I have not encountered a vehicle that requires sensors to be removed at particular cycles or for preventative maintenance. Show me.
"If your car will throw a code for it then go ahead and hold off a bit" What does that mean? If the sensor triggers a code, then you should do something, not wait a bit.
A sensor does not "kill a cat", it only provides an indication that the sensor has sensed something that is outside of the pre-set parameter it was expecting to sense. Sensors are dumb devices. They expect one very specific signal and will only wake up if it has not received that signal...and then it tells the ECU. It does not submit 'ranges" to the ECU, only on or off. Kind of binary.

I guess you have never tuned cars. Having a fully programmable ECU with onboard datalog is awsome, it can tell you lots of thing you dont know.
OP, when in doubt take it to a shop who can read more than error codes. Not all errors throw a CEL.

Not sure what car you're driving either.
Perhaps you are right, I may not have tuned many cars. I do know this, sensors are in a system to report anomalies, not to help you "tune" an engine.
A fully programmable ECU (and all ECU's log data) is a misnomer. You can manipulate an ECU of almost any car with the right tools. You can "flash" any of the chips on board and you can even get "performance" chips but, the program on these replacement chips have been tested and altered with very specialized tools and test equipment and have been analyzed to death to ensure no damage will be caused to the engine. You can adjust the ECU trigger points and all sorts of things but, you also need to know what the consequences are by manipulating even one sensor trigger point.

The O2 sensors on a car are the most misunderstood sensor and so many people think that by changing one, all your woes will be gone. Very wrong. The O2 system is just a system of measuring the effectiveness of the catalytic converter and triggering another part of the ECU to adjust fuel or air or both to remain within the exhaust gas level set for the car.
But, what the heck to I know, I don't tune engines (as opposed to cars) anymore.

[Qube]

Pete, thanks for the comprehensive replies.

BMWs will throw a code for O2 sensor aging when it senses out of spec information from MAF to O2 (pre and post). For this, you can hold off a little bit longer. For example, my pre-cat O2 bank 1 fired off an aging. I cleaned the MAF to ensure that's not the simple issue and reset the code. When it came back, I replaced all 4 original sensors (pre/post cat, 2 banks). It's a BMW 540 with 130k. Fuel economy improved slightly but noticeable (average 13.5 L/100 to 12.2 L/100 same runs daily).

A failed O2 sensor will cause the mixture to run rich, damaging your cats. Once this happens, we're talking big money versus a $80 sensor.

[m4gician]

Thanks guys, I'll hold off until I get a code showing up. I have an ODB-II scanner, so if I see a code, I'll replace then.

[l69norm]

My opinion:

A "lazy" O2 sensor is defined as one which takes longer than 100 mS to go from one end of the scale to the other (i.e. full rich to full lean) during a sudden change (i.e. "snap" throttle test) . It's tested using a scope or a specialized test set as a standard ODB2 tester does not react fast enough. The tester is connected directly to the 02 sensor. Here's an example of a test set:
http://www.gtc.ca/EN/ST05_EN.html

Sometimes when people refer to a "lazy" O2 sensor, they really mean a "biased" O2 sensor. Normally, an O2 sensor is suppose to read a certain voltage to signify a perfect a/f ratio (i.e. 14.7:1 = 0.45v). Sometimes a 02 sensor reads slightly "biased" giving a "lean" signal when the mixture is OK. This causes to ECM to incorrectly enrichen the a/f mixture. It doesn't take much of a long term a/f mixture error to cause a cat problem.

Contamination is what kills 02 sensors. This is caused by fuel additives, old style antifreeze leaks, incorrect sealers (i.e. too much silicone gasket maker), incorrect engine oil (i.e. wrong anti-wear additive), etc

Old school cars (pre 1990) had a high failure for 02 sensors so it made sense to periodically change out sensors for preventative maintenance but anything made since about 2000 is pretty good.

[DragonZealot]

"Lazy" O2 sensors are figment of the imagination of wannabe mechanics. There is no automotive proof of this phenomenon. Well, let me back off a bit, yes, there are O2 sensors that can, for various reasons be slow to react but, without triggering a CEL, it is still within the parameters set out by the vehicle OEM.

I don't think it is an imagination of wannabe mechanics. Isn't this the condition that set off DTC P0133, a code from OBD2, which is a specification from a consortium of automotive engineers and agreed as standard by auto manufacturers.



Sensors are dumb devices. They expect one very specific signal and will only wake up if it has not received that signal...and then it tells the ECU. It does not submit 'ranges" to the ECU, only on or off. Kind of binary.


In the close loop mode the O2 sensor output is varying up and down all the time (like a sine wave). It is not "kind of binary". It does submit a range (peak-to-peak) of the signal. The ECU analyzes the signal and determine if it is lazy (too wide between crossing of stoichiometric points) or out of range.

[Pete_Coach]

My opinion:

A "lazy" O2 sensor is defined .............

Contamination is what kills 02 sensors. This is caused by fuel additives, old style antifreeze leaks, incorrect sealers (i.e. too much silicone gasket maker), incorrect engine oil (i.e. wrong anti-wear additive), etc
..............

I don't think it is an imagination of wannabe mechanics. Isn't this the condition that set off DTC P0133, a code from OBD2, which is a specification from a consortium of automotive engineers and agreed as standard by auto manufacturers.........

You guys are both right and do internet searches real well.
We all know what can "kill" an O2 sensor, and the trigger condition P0133 can be other things too, not just O2 sensor fail. And yes, all this is engineered and yea, there is a governing body.
You need to diagnose the entire situation and the key question you should be asking is "what caused the O2 sensor to trigger the CEL light". There can be any number of reasons and by just stating the O2 sensor failed or it is a lazy sensor you simplify the issue and may cost the customer unnecessary money.
My answers were to the OP and were not to piss you knowledgeable guys off but to answer the OP's question and to inform the OP that he does not have a problem, considering he does not even have a CEL on. Why spend money when you don't have to? In his case, the O2 sensor is a dumb sensor, it is not telling him he has a problem, someone was trying to convince him to change something that does not need to be changed.
.