Can you have a failing o2 sensor with no check engine light?

[1 SX]

Just wondering, previous owner mentioned a check engine light on the Elantra, and i ran the code about a year ago, and came back with a P0139, I deleted it, but it would come back every few days, The car then sat for about that year until i picked it up, I "tuned" it up, sparkplugs, synthetic oil, air filter, stuff like that and red lined it multiple time. I drive much differently then the P/O and am not afraid to exercise the RPM range.. But this o2 sensor has NOT been replaced, and i even swapped it over into the new flex pipe. (code was there long before flex pipe needed to be replaced.)

But im thinking, should i replace it anyways or should i wait until the check engine light comes on again? If i do it now, i know it will come out of the exhaust pipe no problem. The sensor is about $90, and i can do it myself. Gas mileage is i think not great, at about 26.4 MPG on avg, but again I use the whole RRM range.. So i dont know if its my driving, or if the slow response on o2 sensor, or probably a combination of both why my mileage is not over 30.

Thanks for your input!

 

[ctechbob]

I would say that its possible. The only thing I have to base that on is my 2003 Accord. If the wife drives it, it will set a P0420 cat code, but if I drive it and drive it hard for a while the code will clear. I would think that it is entirely possible for an O2 to be just on the edge where lower speed driving will foul it just enough to throw the code, but good hard hot driving will keep it clear.

 

[1 SX]

I would say that its possible. The only thing I have to base that on is my 2003 Accord. If the wife drives it, it will set a P0420 cat code, but if I drive it and drive it hard for a while the code will clear. I would think that it is entirely possible for an O2 to be just on the edge where lower speed driving will foul it just enough to throw the code, but good hard hot driving will keep it clear.

That's exactly what Im thinking! The P/O was a gentle driver and would never go over 3K, but since i owned this car, that light has never came back...

Maybe i should just replace it, before it welds its self into the pipe again! (Although i did use A/S on threads when swapping it over)

 

[Kira]

With some reading I found 12 years and 100,000 miles is when they can go.
I DO NOT know if all the different oxygen sensors have the same lifespan expectations.
I am changing the 2 upstream sensors in my V6 because they're 16 years old (with only 53K).
Big deffo on changing yours now before rust welds it in place forever.

In cases where codes are set by different drivers (your case) I'd conclude the sensor was beyond borderline bad but that's just me.

Ha-ha P0138 was the very first code I ever pulled; the upstream O2 on sis' Jeep Cherokee.

 

[Jetronic]

Yes its possible, at least here in Europe.

For example had a lancer in a few years ago with no cel but failed emissions. Was running lean and the live data showed me the main o2 sensor was sluggish. changed from lean to rich slowly. He had a new engine in that year and the replkacement wasn't identical as that one wasn't made anymore, so for a bit people thought it was due to the different head and block.

In fact i've rarely come across an o2 sensor failure that triggerede a cel, but then anybody can diagnose it then.

 

[Skippy722]

My 2012 Caliber started getting horrible fuel economy, like 20mpg no matter how nicely I drive. Fired up Torque and noticed the upstream o2 sensor seemed to be reading slow…. A new NTK sensor and my fuel economy was back to the normal ~25mpg. Never tripped a CEL or anything… happened right around 90,000 or 95,000 miles.

 

[1 SX]

I think i get the picture here haha!, Im going to order a new sensor, and change it out today!. Car has 114.5K and has original sensor.
Thank you all!, Will update when new sensor is in.

 

[swampdodo]

Yes. They don't necessarily fail and trip a CEL, but they can, over time, get 'lazy' and cause things like bad MPG. I've heard that some recommend replacing them as part of a 'long interval' tuneup like changing plugs just to keep a vehicle in 'top running shape'. But they can get expensive.

 

[1 SX]

Yes. They don't necessarily fail and trip a CEL, but they can, over time, get 'lazy' and cause things like bad MPG. I've heard that some recommend replacing them as part of a 'long interval' tuneup like changing plugs just to keep a vehicle in 'top running shape'. But they can get expensive.

The "upstream" 02 sensor is over $245 so i will see if this downstream sensor fixes MPG. If not upstream it is!

 

[Jetronic]

the downstream doesn't affect engine running, it's just checking the cat is there and working

 

[SHOZ]

The downstream sensor will set P0420 codes.

if you have a way to see the real time OBDII data then monitor the O2 voltages. Post cat should stay above .500v for the most part but should stay just below the max you see on the first O2 sensor.. Pre cat should cycle from ~.050v to ~.750v, 3 times per second approximately.

 

[mightymousetech]

Absolutely possible. Have seen it often. With high mileage they get slow, most manufacturers recommend replacement around 160k as a maintenance item. Just replaced all four sensors in my E90 with 200k km.

 

[Kira]

A service writer told me, "The front one always goes first". Ergo, there's constant demand for them.
My Volvo's front sensor listed at $238 but I found a DENSO (sensor had DENSO & Volvo written in the ceramic) replacement for $160ish.
Volvo part places have sales. Don't know about Hyundais.

 

[Trav]

the downstream doesn't affect engine running, it's just checking the cat is there and working

It can, there are dual systems that also utilize the rear o2 for mixture control. O2BxS2FT is a rear o2 fuel trim PID. There are things like this written about it. This is getting more common.

Since Toyota allows the rear O2 sensor a surprisingly large authority over fuel trim, you’ll want to test it carefully as well.

The first time I can remember running into this was on an Infinity back in 06.

 

[ARCOgraphite]

Before wideband, yes. It's output was taken as fact. If it was out of range or slow the light throttle cruise performance and mixture would suffer.I usually see then running rich. Load misture is from lookup and IAT, MAT or maf or both, RPM, throttle angle

 

[NitroM3]

First there is a difference between a O2 sensor and a more commonly used HO2 sensor. It is almost impossible for a failing primary HO2 not to cause an ECU generated DTC. And it is NOT common for that to happen. Nor is it becoming more common! If anything the programing regarding ECU is becoming more accurate! Any real and current certified Auto Techs. go read the latest information(ASE reports) about ECU and sensor reporting to the ECU and specifically HO2s. Now O2 sensor sure they could have a problem reporting because of contamination or age to the ECU because the ECU of the time using O2 sensors (not HO2's) were not as complex programming as from 2001 and newer manufactured vehicle's. The OBDI were not very predictable or accurate for ECU DTC reporting OBDII and CAN-bus are.

The primary HO2 fails predominately first because of a higher exhaust temperature it operating in. Then contamination to name a few like a build up of unburned fuel or an engine that is using oil like worn valve seats or dirty fuel injector allow to much fuel in the combustion chamber and incomplete fuel ignition.

There is no such thing as a lazy HO2?? Really ? LOL
If the HO2 becomes contaminated the reporting information will not be accurate but the report speed (which is an electrical current) will remain the same. Can't change the physic's of electricity LOL


For the geeks that like to bolt on power parts (like me) what do we all have to do to the HO2 often so we dont get a DTC?
Trick the ECU because the reporting of the HO2 is so accurate that unless we relocate or other similar methods to fool the ECU it will DTC us!

 

[NitroM3]

First there is a difference between a O2 sensor and a more commonly used HO2 sensor. It is almost impossible for a failing primary HO2 not to cause an ECU generated DTC. And it is NOT common for that to happen. Nor is it becoming more common! If anything the programing regarding ECU is becoming more accurate! And real and current certified Auto Techs. go read the latest information(ASE reports) about ECU and sensor reporting to the ECU and specifically HO2s. Now O2 sensor sure they could have a problem reporting because of contamination or age to the ECU because the ECU of the time using O2 sensors (not HO2's) were not as complex programming as from 2001 and newer manufactured vehicle's. The OBDI were not very predictable or accurate for ECU DTC reporting OBDII and CAN-bus are.

The primary HO2 fails predominately first because of a higher exhaust temperature it operating in. Then contamination to name a few like a build up of unburned fuel or an engine that is using oil like worn valve seats or dirty fuel injector allow to much fuel in the combustion chamber and incomplete fuel ignition.

There is no such thing as a lazy HO@?? Really ? LOL
If the HO2 becomes contaminated the reporting information will not be accurate but the report speed (eclectic) will remain the same. Can't change the physic's of electricity LOL





For the geeks that like to bolt on power parts (like me) what do we all have to do to the HO2 often so we dont get a DTC?
Trick the ECU because the reporting of the HO2 is so accurate that unless we relocate or other similar methods to fool the ECU it will DTC us!

Now for the SUPER GEEK or people that have some experience with ECU Calibrating if we use a program and tool plugged into ODDII diagnostic connector for full ECU access all we need to do is turn off the HO2s. No no more DTC regarding them ever! Unless you turn them back on. LOL

 

[2009 GLS]

Update: new o2 sensor is installed will update any changes. Thanks everyone!!

 

[1 SX]

Update: new o2 sensor is installed will update any changes. Thanks everyone!!

Update: Is it possible that this new O2 sensor makes the car more responsive in the 5-35% throttle range? It feels more "peppy" now without giving it a ton a throttle.

Also really odd it comes up under a different user name?

 

[SHOZ]

On my Accent I rode the last one into the dirt until it stopped working completely. I watch the voltage constantly with a ScanGauge. You really can't see the slowness as the gauge can't keep up, but sooner or later it starts to hover around the same number and finally quits. The ECU takes over and puts out a constant .450V and goes to a default fuel table to keep the car running. It then turns on the slow/no response check engine light.