Scheduled Replacement of O2 sensors

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I read this online:

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Heated three and four-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. And on 1996 and newer OBDII-equipped vehicles, the recommended replacement interval is 100,000 miles. A good oxygen sensor is essential for good fuel economy, emissions and performance.


I've noticed over the years on my (older 1-wire O2 sensor) vehicles, they start to experience fuel economy degradation long before the oxygen sensor is considered 'bad' by the ECU and a code thrown. I think I'm well ahead of the game by throwing a $20 oxygen sensor at such vehicles every 50k than paying for it in the form of lower MPG. Most of my fuel is bought at $5+/gallon over the past 10-15 years, so loss of efficiency really does add up!

On a (new to me) vehicle, that has 110k on its 4-wire heated O2 sensors, I am contemplating replacement. Even though the cost is considerable ($150 for parts!).

Anyone else do this, change O2 sensors by distance (miles) travelled, rather than waiting for a CEL (or failed emmissions testing) to force the issue?

Of course the manufacturers *never* put oxygen sensor replacement in their owners manuals.
 
The upstream sensors get lazy as they age. Replace just the upstream sensors, you may only have one or two instead of two or all four. The downstream sensors don't really need to be replaced as they don't really wear out, when they're gone, it means the cats are gone.
 
I've been thinking about replacing my O2 sensors as well, because my car has 117k miles on it now. No codes, though. My reason is somewhat different: I'm going to be moving within the next 5 months, and I'm downsizing dramatically. I'm not going to have a garage in which I can comfortably work on my vehicles. I'm only keeping a small set of sockets and power tools. I would hate to take my car to the dealer for something as simple as O2 sensor replacement. [censored], I've been thinking of preemptively replacing the starter and alternator!

That being said, I have a '06 Camry with 180+k miles and no CELs for O2 sensors (or anything else). Makes me think that my O2 sensors might still have a little life left.
 
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I am a recent convert to this way of thinking. I acquired my current vehicle after it had already spent the first 100K miles of its life as a city police squad car, and while there were no O2-related DTCs or faults in the system, I decided to replace the upstream sensors with new ones anyway. I started a few threads on various different automotive forums declaring my intent and inviting discussion on whether or not I was being prudent, foolish, wasteful, etc.

Not surprisingly, the feedback I received from every thread was mostly the same regurgitated, out-dated opinions, most of which stated the sensors should be left in until failure. Even less surprising, I was provided with NO evidence, other than anecdotal, that could convince me the O2 sensors were somehow immune to wearing out gradually like other sensors on the car. So I went ahead and did the unthinkable - I purchased non-OE parts from a local parts house** and replaced the upstream sensors despite their seemingly robust health.

Well, let me tell you, just because the O2 sensors seem to be behaving fine, and there are no active (or inactive) O2 sensor faults stored in the PCM, that does NOT mean they don't need to be replaced. The tips of the sensors I pulled out of mine were covered in cement-looking deposits that I couldn't remove without a stiff wire brush or file. I don't know what caused them or how much they were affecting the sensors' operation, but there is no chance they weren't affecting the sensors' operation to some extent. Maybe not enough to cause it to throw a fault, not yet anyway, but those senors were not doing their job like they did when new, that's all there is to it.

By the time I finally got around to doing the job, the engine had about 130K miles it, and I had estimated the sensors should fall into the 100K mile maintenance service category, so while I may have been correct to think they needed it at 100K miles, it is likely they were losing some functionality well before that. YMMV obviously.

I would love to have some Before and After datalogs showing real proof that replacing my sensors before they failed was the right thing to do, but I don't. I tried to record some datalogs for that very purpose, but I could not get the PIDs necessary to log data showing the O2 sensors' output in an understandable way, so I gave up.

I can say my average MPGs for city/hiway mixed driving went from 18 MPG at time of replacement to 20 MPG now. That wasn't an immediate jump, but more of a gradual one that took several weeks to come on. No other performance mods have been performed in the interim, heck, the air filter is even still the same one. The average ambient air temp has increased significantly since I changed them out, so I would have expected a decrease by a few MPGs actually by now. But that is not the case - it is burning the fuel at a slightly more efficient rate than with the old sensors, and the sensors are the only variable that has changed (besides weather).

Go ahead and do it, it certainly cannot hurt to have new sensors in there - that's my position on this subject.

Nuke


** -I will note that I decided not to buy the sensors from the dealership parts house mostly due to their price point. The Mopar branded O2 sensors were over $80 each from them, so I would have had to spend close to $200 for parts alone to go with OE sensors. Instead of doing that, I went with the NTK branded equivalents purchased at a local automotive shop (O'Reilly Auto), and spent almost $40 each for those. So basically half the price of the Mopar branded ones. I could have ordered them off Amazon and saved even more money if I truly wanted to.

I did have the benefit of knowing beforehand that the Mopar branded sensors are made by NGK and re-branded as Mopar, or that's the conclusion I came to after doing some research on the matter. I also uncovered, during that research, that the aftermarket brand NTK is NGK-made-and-rebranded as well. So basically I believed (and still do) that the NTK O2 sensors were the same as the Mopar ones, and that was what pushed me over the edge to go with them.
 
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Maybe true for OBD-I cars pre-1995, I would "think" OBD-II systems can better detect when an O2 sensor is getting flaky. I'd wait for the code.
 
Originally Posted by Lubener
If it isn't broke, I'd leave it alone.


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Mine weren't broke, but they were breaking, and that's with only 130K miles.

I do not want the sensor to dictate when and where I perform the replacement when it is no longer functional.

I prefer to decide the when, where, and how of that so I can orchestrate it to my advantage, i.e. do it in my garage on a day off as opposed to in the middle of a trip, in some other town late at night on a Sunday, without proper tools.
 
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I have not done proactive replacement but my cars are late model OBDII vehicles that see mostly highway. YMMV but they live gentle lifestyles. I did replace one as I decided to watch the O2 signal on Torq to see how it looked, and since the sensor was dead (but not throwing a code!) it got replaced.

If nothing else, there may be value in cracking the sensor loose and reinstalling but with antiseize. In case of future replacement.
 
Originally Posted by Egg_Head
Maybe true for OBD-I cars pre-1995, I would "think" OBD-II systems can better detect when an O2 sensor is getting flaky. I'd wait for the code.


How would the PCM alert the driver to this flaky condition? Set a DTC with a message like "slow responses detected; prepare for sensor failure at some point in the future"??

No such codes exist that I know of.
 
Older ones I would replace at 100k. But newer 4, and +, wire heated O2 sensors I don't change unless I get a code or they read lazy/bad.
 
Originally Posted by pitzel
Of course the manufacturers *never* put oxygen sensor replacement in their owners manuals.

I have seen where BMW lists an O2 sensor change at 100K in their service schedule.
 
I haven't had a high mileage vehicle in 5 years but in the past I replaced them on a Rainier, for maintenance.

I guess it depends on the cost. The Buick's were less than $80 for both, my VW shows $350! If I had a V-engine with 4 sensors I would probably wait until failure.
 
I have been grappling with some of these questions myself.

I've basically decided its not a bad idea to change out before it actually gives you problems.
So, while they say the life is 100k, you can probably go 120-150k or so without any real problems, and not much loss in efficiency.
I read an article that claimed it would pay for itself in improved gas mileage, but i'm skeptical.

As far as what to look for - I think OBD2 can report sensor stats, etc. You might look at fuel trims. Not really sure, would appreciate more advice on what to look for specifically.

I will be changing mine out at 120k (in the next month) and will report back if I remember to.
 
They're too expensive to make up for potential fuel economy gains. There's no way $150+ is going to be recouped in fuel if you replace them at 100k. You might not even own it by 200k.

We're talking what? 1-3 MPG gain that will taper off as the new O2 sensor ages.
 
If it makes you feel better great and keep car longer better.

That being said my parents never touched o2 sensors in their 2000 Tundra v8 and 2000 Subaru Forester. They run without CEL's.

Myself running OEM o2 sensors on my previous 1995 Civic Ex/2005 Subaru Legacy and current 07 MDX all with 200k+. No related CEL's.
 
Originally Posted by KrisZ
I have a log with every fillip and my mazda 3 still gets the same highway mpg as it did when brand new. No reason to change anything just because of mileage.


Same goes for Timing belt, water pump, serpentine belt, associated pulleys - ain't broke, leave it!
 
Originally Posted by madRiver
If it makes you feel better great and keep car longer better.

That being said my parents never touched o2 sensors in their 2000 Tundra v8 and 2000 Subaru Forester. They run without CEL's.

Myself running OEM o2 sensors on my previous 1995 Civic Ex/2005 Subaru Legacy and current 07 MDX all with 200k+. No related CEL's.


That's great, glad to hear everything is going good...but the plural of anecdote is not data, not for me anyway
 
Originally Posted by The_Nuke
I do not want the sensor to dictate when and where I perform the replacement when it is no longer functional.

I prefer to decide the when, where, and how of that so I can orchestrate it to my advantage, i.e. do it in my garage on a day off as opposed to in the middle of a trip, in some other town late at night on a Sunday, without proper tools.


There is no need for that. It will simply run in open loop mode, and use more fuel till you get it fixed.

As far as mileage, you can't really go by that. It'll be significantly shorter if the engine burns oil or with a lot of short trips, and yet those who put on a lot of longer mileage trips have the most to gain once their sensor is near the end of its useful life.

If you've owned the vehicle long enough you can track fuel economy to notice when its getting lower, and go ahead and replace the sensors just in case that's the cause, but until they fail the fuel economy difference will be so slight that you'd have to drive a very regular routine to notice that small a difference.

If you just bought it used with 110K mi., and it's not a beater (sub-$2K value), personally I'd go ahead and replace the upstream sensors if there is no record of that being done in the past. This establishes when it was done, was close enough to needing done (cost/year since you just bought it rather than contemplating getting rid of it sooner than later) and gives you that much longer till it needs done again. The same could be said for wires, plugs, fluids, etc. at 100K mi.
 
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