Oxygen sensors eventually need to be replaced in all vehicles. If your vehicle’s O2 sensor is faulty, chances are there will be signs! Check this list to see if it’s time to replace YOUR vehicle’s oxygen sensors:

  1. Sudden decrease in fuel mileage. A defective O2 sensor will likely cause your air-fuel mixture to be too rich and directly affect your fuel economy.
  2. Flashing check engine light or malfunction indicator lamp in the vehicle?s dash board. Of course this can happen for other reasons as well (and a defective oxygen sensor is one of them!)
  3. Failure to pass smog. According to the EPA (Environmental Protection Agency) and CARP (California Air Resource Board) 50 to 60% of all smog test / emission test related failures are attributed to defective oxygen sensors, causing either low or high CO emissions.
  4. Overall poor vehicle performance; rough idling, stalling, hesitation on acceleration, etc.
  5. And the most accurate diagnosis is achieved using an OBDII code checker. All cars made in 1996 and after are equipped with an OBDII interface. An OBDII code checker identifies defects in the exhaust system of the car. If your oxygen sensor has failed, the code checker will generate a diagnostic trouble code that specifically indicates your oxygen sensor is bad.

Guidelines for replacing the oxygen sensors in your car, courtesy Bosch.com:

  • The unheated 1 or 2 wire O2 sensors, used in vehicles from mid-1970s through early 1990s, replace every 40,000 to 50,000 miles.
  • Heated 3 and 4 wire O2 sensors, used in the vehicles from mid-1980s through mid-1990s, replace every 60,000 to 70,000 miles.
  • Newer vehicles made in mid-1990s and later, replace the oxygen sensors every 100,000 miles.

Conclusion, properly functioning O2 sensors are critical for optimal fuel consumption and good car performance. When in doubt, it is best to replace your faulty oxygen sensor at most, every 100,000 miles.

  • http://pulse.yahoo.com/_6C3WGWXISBYXTPG7NR6LVQ6PDQ Margaret Miller

    A very informative post on oxygen sensor. My car’s oxygen sensor was replaced several times. With these signs, I can now assess whether my car is really having oxygen sensor problems. Thanks!

  • http://www.bes.co.uk plumbing

    These are very helpful notes to remember. I will surely apply this at home.

  • chris

    i recently changed my af sensor and the cel came on again reading the same code prior what do i do now

    • N00b334

      Have you tried restarting your ecu by disconnecting the positive battery terminal? Then restarting the car and allowing it to idle for ten minutes? I’m not a

      • jujuboy

        tried your suggestion “disconnecting the positive battery terminal”. That was 5 years ago. Have tried to restart every day for the last 5 years. Do you think that I should have reconnected the positive battery terminal before trying? You didn’t say that, Chris! Maybe I should seek professional advice. My tires are starting to go flat and the parking tickets are fast approaching what I paid for the car in the first place. Also, parked beneath a tree and the bird poop is deep enough that a small bush is growing out of my windshield wiper space.

  • Klhoepsin

    Heated O2 sensors are recyclable…they have a little bit of platinum in them which makes them more valuable than most scrap metal. (they are only worth 50 cents or so) Bring yours to your local repair shop so they can add it to their collection bin – both the technician and the environment will thank you.

  • http://profile.yahoo.com/OXMIE4DITSQWIG2VRI5PPDXQEE John w.

    My 1995 Bonneville stalled and also died when I made left turns. Took it in they said it was the oxygen sensors. It ended up costing me a thousand dollars to get them replaced because they were not accessible. If I had a 1996 Bonneville it would of cost around two hundred.
    Car ran fine afterwards.

    • Josh M.

      You got ripped off. I have the same car. The one O2 sensor is behind the engine on the exhaust manifold, not hard to get to at all. I always tell people to ask on forums first and friends/family after.

  • tamara

    i can be going down hwy and lose power will die and pull over and starts back up sometimes it will shake and not have enough power to accelerat but after a couple of times will start up and run just fine what could be wrong

    • Austyn

      Does not sound like the 02 sensor

      • Brian Vi

        You sure? I have the same symptoms and got the error codes:
        P0420 = Catalytic convertor, or a bad O2 sensor
        P0430 = Catalytic convertor, or bad O2 sensor, or a leak in exhaust.
        Could also be a bad EGR VALVE.

    • Austyn

      Does not sound like the 02 sensor

    • Freddie

      Sounds like a bad EGR.

      • Dianne

        What is an EGR?

        • LUV2SKICO

          Exhaust Gas Recirculator. If it gets stuck open, it will drag down your O2 level as sensed before your upstream catalytic converter. The ECM (engine computer) will interpret this as a too rich fuel-air mixture (which it’s not) and try to compensate by making your air-fuel mixture even more lean. This starves the engine of the fuel necessary to run effectively.

          Many newer vehicles with VVT (Variable Valve Timing) don’t have an EGR. Instead, they leave the exhaust valves open briefly during the intake stroke drawing in a little bit of exhaust gas to mix with the intake air-fuel mixture. This effectively does the same job the EGR used to do and is more reliable than the EGR.

          The easiest way to tell if you have an EGR or not is to look up EGR for your vehicle on a site like Rock Auto, NAPA, AutoZone, etc.

    • Twinkie

      It’s a cps. 100%

      • Kathy Stuart

        What CPS?

    • Joshua Fennelly

      Crank shaft positioning sensor. Mine did the same cheap repair if done by yourself.

    • Joshua Fennelly

      Think the part cost me 20.00 for the crankshaft positioning sensor it took me 30 min to change.

    • RaKeril’s Gaming

      check ur fuel pump, i have had two cars that did this an each time the fuel pump was going

    • Brian Vi

      i have the same symptoms, engine shuts off while driving, i coast over to the side of the road, count to 60 and then it starts back up again, i go about 1/2 mile and it does it again. I got the 2 error codes (codes P0420 & P0430) which commonly mean Catalytic CONVERTER – OR O2 SENSOR. since my Catalytic converter is new, i’m thinking it’s my O2 sensor OR Could also be a bad EGR VALVE. i have a 1998 Honda CRV.

    • Dr Y

      This seems fuel pump issue and require changing. Fuel pump filter need cleaning.

    • Jordan

      Or it could be a dirty air filter mine would cut out at 160 thought it was govern but nah changed the dirty are filter and bam she can move past 200

  • Ashley

    when trying to accelerate the car seems like its not accelerating, was told either the O2 sensor or the wiring to it needs replaced. What will happen if the cars o2 sensor is out? Will it have issues accelerating? like i can accelerate but its not going above 25 to 30 without making it seem like the car is in park and pressing the gas pedal. So I guess what im asking is since the O2 sensor is bad could this be the reason were having acceleration issues…other than that the car runs and drives fine

    • Christopher Bryant

      I Have the same problem if you have found out any thing please let me know.

      • Jeff

        Bad o2 sensors, clogged catalytic converters and a host of other failures can cause those symptoms. It’s hard to tell without codes being set. If you have access to a diagnostics scanner that reads live data, watch the o2 upstream data as well as the downstream o2 data. The upstream should move up and down indicating that its good. If the downstream is moving up and down like the upstream, then the catalytic converter is shot. If the downstream is steady, then the cats are working. You will need to know what the proper voltage is for your o2 sensors to determine if they are working as they should.

        • debi

          my son had the same thing and it was the clogged catalytic converter

          • Jeff

            Usually when a cat goes bad, you will smell sulfur. Theirs several ways to figure out if the cat is bad. You can loosen up the bolts in front of the cat to the intake and see if it runs better. You can drill a hole in the cat as well to see if it runs better, then plug the hole. You can use a thermal gun in front of and behind the cat. If it reads hotter behind the cat than it does in front of the cat, then the cat is clogged. The downstream o2 sensor’s job is to monitor the catalytic converter. Most mechanics will often say it’s the o2 that is shot when it is actually the cat. When the cat is restricted, the downstream o2 will show bad readings. Understanding downstream and upstream, LTFT (long term fuel trim and STFT (short term fuel trim) live data is something that A LOT of techs don’t understand.

          • mike

            you got it backwards
            it should be hotter after the catalytic converter that’s why you see water coming out the exaust because it has to be hotter to burn the fuel.
            a good cat you could get behind the exaust and smell it all day long but with a bad cat or no cats exaust will burn your eyes and you cannot breath it.

          • Jeff

            I just realized that lol. Clogged cat would be hotter upstream.

        • arejaye

          The mechanics that checked my car out mentioned it being the upstream O2 sensor, so after that and reading everything here, I’m gonna bite the bullet and change it out and HOPE I’m not gettin’ screwed. Livin’ on disability is tough enough and there’s no such thing as “extra money”. To everybody, thanks for the info!

        • Memo Muñoz

          I seem to have that type of problem with my downstream O2 sensor. When i smogged my 97 gsr HC NO were high and CO barely over the MAX.

    • arejaye

      I just inherited a ’95 first gen. Toyota Avalon with 125k original miles but only about 70k miles on it’s engine, but already having some of the same issues you mentioned. The car starts and runs GREAT except for what I think is a high idle when first cranked in the Summer(it takes about 4 mins to idle down to what feels/sounds normal w/ no A/C on), but…if I have to drive up a hill, which are numerous around here, it acts like I’m towing an 18 wheeler with a full tanker on it, and the car’s A/C on. A few days ago I took it head to head with a fairly new Mustang from a stop light, and if he was pushing it equally as hard as I was, it was a tie. (Not bad for a 22 year old car with no known mods to the engine.) Even switching the power on the transmission there’s little difference. I had it checked a couple days ago and they said it was a bad O2 sensor. The only upside to no power going UP a hill is that there’ll be no problem coming down the other side and hoping the brakes and parachute work like THEY should!. LOL

  • Steve ram

    I replaced my oxygen sensor and my CEL went off but when I used my scan tool it reads yellow an will not pass an emission test, help!

    • Dyler_Turden

      I know this is an old post, but did you resolve it? I believe you have to complete a certain number of drive cycles before the “warning” is removed from the OBC memory…

    • blown 406

      Did you reset the computer…after replacing any electrical senors you always go back and reset the computer with a scan tool and drive it for at 3 days before going back to test it.

  • Kathleen

    My kia stalls out when I’m getting gas and them won’t turn over at first. It takes a couple of tries and giving it a little gas to get itto keep from stalling. Could this be my o2 sensor?

    • Chris Smith

      Hi, it could be as easy as a gas cap. Others would be injectors, fuel pump is weak, dirty fuel filter. Did u get a C.E.L.

  • Mack

    My truck stalls out and after 5 minutes are so she starts up and then stalls again after a few minutes. I thought I got some bad gas and add some sea foam and it ran good for a short time and then started stalling again. Auto zone tested to see if a code would come up and it did not show any. Can the oxygen sensor be going bad and not show a code? Thanks

    • Jeff

      Yes, however, I doubt a bad o2 is causing your issues. Sounds like a fuel restriction.

      • Miracia Vladimir

        I have the same issue. Car starts after reaching normal temperature it dies.After starting back up it will die again. However, when i disconnected both front o2 sensors or the EGR valve it works fine.Do you have any idea what it could be?

        • myxolydian-minor

          either the egr or the o2 obviously ,if you diconnect them and it runs good and when you reconnect them and it runs like ass that tells you the parts are bad.

  • nathan

    i aint sure its my o2 sensor or not but my 1999 gmc serria runs fine except upon heavy acceleration or when its under a load like going up steep hills ive been told its some type of sensor or its not getting enough gas any ideas

    • Jeff

      Misfire perhaps. Bad coil pack or plugs. Intake leak.

  • david

    I had oil getting through my intake so I had engine rebuilt but it was smoking like crazy before the rebuild and engine light is on it says cat is below efficiency any idea what it is?

    • Snowman

      IF your car was burning lots of oil then that burnt oil clogged your catalytic converter. New cat needed.

    • April

      I have a 2000 Chevy astro after 3 days of purchase it started to loose power w hi ile driving and then completely stall…but pull over and it would start back up would be fine for a while then do again…then started happening more and taking longer to start well yesterday it stalled and wouldn’t start back at all..would turn over.. I have no lights coming on the dash at all all gages look fine..we have changed fuel filter puut sea foam in gas checked for loose wires my husband took one of the o2 sensors off thought that was the problem car started and drove good well today it started and then stalledvtwo Ty times took a while to start but made it home please help

      • April

        Also he checked the distributor cap and that was good

      • larry

        Have the ignition module tested it could be bad as that can cause it to stall and restart and then quit altogether. Hope this helps.

    • Jeff

      Bad catalytic converter.

  • Heavyweight

    Hi Everyone,

    I own a 2002 Honda Civic LX 1.7L Manual. I suspect the problem with my car is the 02 sensor. I got a OBD reading of P0132 02 Senso Circuit High Voltage, Bank 1 Sensor 1. This is the obvious diagnosis given the error code but I was wondering if the problem could be something else. The car stutters and bucks when I accelerate in 1,2, and 3rd gear up to about 3k RPM. Also, when I idle, the car jerks and feels as though it will stall. Is there a good chance it is the 02 sensor or could it be something else or in addition to the sensor?

    • yolanda

      my car is doing exact same thing its a 2002 manual transmission 2 door … what do I do? yolandarosetta@gmail.com please help

      • Jeff

        Is your check engine light on? If so, what are the codes?

  • Pete Brooks

    this sensor is crazy, and it does a lot of things for the car and transmission. my mechanic thought it was the tranny so he changed out the torque convertor kit. that fixed about 80% of the problem. but it’s still acting jumpy. it will shift when it shouldn’t and it idles high when i start it. he hooked the computer up to it today. there is no check engine light although the check engine system is working properly. it reads zero on the oxygen sensor, even when he revved it to 3,500 rpm. I’m sure when he replaces the sensor in two days my problem will be fixed!

  • Ragofmuffin

    I have a 93 chevy Cheyenne that has a fluctuating rpm at idle. & usually it happens with engine gets up to operating temp. O2 sensor or what ?

    • Jeff

      MAF sensor, EGR valve or vacuum leak between the MAF and throttle body. Most likely the MAF sensor.

  • Tim

    Would a bad 02 sensor cause the mustang to run sluggish stall out and not stay at a steady idle

  • Tim

    Would a bad 02 sensor cause the mustang to run sluggish stall out and not stay at a steady idle

  • reid newton

    screew yall

  • reid newton

    pussy? 940-631-3559

  • Brad Nimbus

    I have a 96 F-250 and it IS in fact OBD l

  • http://www.fuckyou.com/upyours The anti-everything guy

    Hey mabey you guys can help me …. bare with me … I just recently cleaned the CARB ON MY DODGE RAM 91 3.9l v6 and it was running like a champ … so I was feeling good and decided to get a new oxigen sensor since my carb was clean and to get a good reading … went to the car parts store and the guy sold me a generic one , well thats when things started , at idle it almost chokes out and then it revs up and starts the loop again , changed the throtle posision sensor for a new one , also took a look at the map sensor and it seems to work and also gave a clean up on the idle posision sensor ( it looks like a solenoid with a bolt head coming out )now after all that when my throtle positionsensor is conected and I disconect the map sensor vacuum hose the problem is mitigated a little and runs a bit smoother but if I disconect the throtle position sensor and re conect the map sensor vacuum hose it runs good agian . So to summarize, is this because the oxigen sensor is not the right one ( I connected the cables identical to all the instalation guides i could find on the net) or is this some other problem ? I would hate to go get a original part ( generic cost 250 pesos ( I live in mexico) but the original is something like 800 pesos) please if any body has an idea please share .

    • boki

      I am a technician on 00 till 2006 on hondas oxygen sensor go out alot I got a 2000 accord the car would shake really bad going 65 70 mph I changed both of the oxygen swnsors Is driving smooth and my gas mileage improved easy fix

    • boki

      Replace both oxygen sensors you always wanna go with the original parts

  • teri

    I have a question. I have a 2002 Lincoln ls. Was told that my O2 sensors were bad, so I replaced 2 of them and when I had the money to get the other 2 I bought them. But I still drove my car. So when the other finally got put on, well my car still acts the same as it did before I replaced the bad ones. So my question is: did I ruin the first 2 I had put on by driving it before I could get them all on. I have uncooked the battery.with no success! Please help! Thanks Teri

    • Steven

      Better re-cook your battery.

  • Thomas Lavrenz

    2004 chevy tahoe misses very badly when sitting at a stop light. Normally idles at 1000 but cuts out down to 500 and sometimes dies all together. When it misses like this the lights dim as well. The weird thing is it does not do it during the summer or when it is first started in the cold winter mornings. The minute the vehicle warms up though (only in the winter) it starts missing badly. Does not act up when driving down the highway. Anyone have any ideas. Had a diagnostic done at local auto parts company and all they can show me is that they say the code reads omission problems. Check engine light is on. To me if it were an O2 sensor I would think it would happen all the time. Any suggestions…

    • thesmoothone

      a year later i know…mines is doing the exact same thing…i am replacing the fuel pump/02 sensors and fuel pressure regulator this weekend. Mines is a 20 year old car but the symptoms are similar…i didnt notice this happening until after i got some gas and added treatment to the fuel system. Its been going on a week and ive added more gas since this so i dont think its bad gas.. Im not getting any engine lights but go to advance or something and check your codes, its free there. Let me know if you have any updates of what was the cause…thanks!

  • kelly

    well i was really not aware of these 5 signs. thanks for the information.


  • tschay

    hi everyone i have a 2002 taurus. the DTC’s say all 4 heater circuits are bad and the evr circuit are bed any ideas or what to cheak. help please i never seen this before or do u think the computer is bad?????????

  • Traci Price

    Stopped and got gas at a place outside of my town.. My car was running fine until I got gas the price was cheaper so I got that gas.. My car started running badly.. Like when I pushed on the gas it was bogging down.. Felt like it was plugged.. I put fuel injector cleaner in my gas tank and a good mid premium gas.. It ran worse and now engine lite is on all the time. Help!! Lol oh yeah it’s a 2002 sonata

  • russell

    I have a 2003 Lincoln LS and the wrench light comes on when I turn the car on as I go to drive it lacks power but if I turn it off an restart it runs fine

  • Melinda

    My 03 Nissan Xterra started completely losing power to where it would shake and die. It would take some time to start back up and would run fine for a while, and then it would do it again. Replaced the fuel filter, pump, and sending unit. It is now throwing a P430 code. It is running pretty good, but now I noticed I am losing about 15 mph going up hills that I used to only lose about 5 mph. Think it could be the O2 Sensor?

  • Rick Herman

    Have a 97 chevey blazer changed fuel pump fuel filt. And fuel presser reg new coil pack and throttle pos sen and still when i get up to 55 mph it bogs and when i let up and ease into it it will go but if i push down agin it will do it agin any ideas

    • Rick Herman

      Just got plugs wires rotor and rotor plug

  • Magnus Soevgaard

    Cars always cause problems when you least need them.

  • kenny kirouac

    hi I have 2001 chevy cavalier I replaced the spark plugs yesterday my mechanic told me about 5 months ago mt 02 oxgen sencer was going after I replace the plugs the car ran bad so doy think I should replace my 02 sencer?

  • Ben Russell

    Ben I have a 1995 cheverlet 350 5.7 silverado 1500 it runs ruff and stall out at red lights and slow traffic do you think it the 02 sensors.

  • Ryan Muhlenkamp

    With my 2004 dodge ram 1500 4.7l magnum I’m having issues with power when I’m going 60 everything seems fine but when I got 70 75 on Highway a small hill causes the rpm to go up because it can’t keep a constant speed.. when I try and give it more gas when I hit the hill it does nothing my mpg is fine when I’m doing 60 but 70 and up it take a massive crap I’m lucky if I get 13mpg highway any ideas? No rough idle, tune up already been done..

    • myxolydian-minor

      slow down,lol

    • Nopchere

      If not fixed yet have your transmission checked. A bad trans will slip trying to go up hill.

  • Shane

    I start my 89 Silverado. Starts and runs fine. Turn it off and restart ii. It runs like a totally different truck. Rough idle,hesitation,,rich smell. Changed the MAP,and IAC????

    • Jeff

      Sounds like MAF sensor.

  • Steve

    Starts up and revs high, Then it seems okay until I reach a speed from 55-65 and it seems like it looses power and intermittently feels like a misfire at idle. Is it my O2 sensor? I get a Code of P0300 Multiple misfire.

    • Jeff

      Look for vacuum leaks around the intake. Are you losing coolant or using a lot of oil?

  • fourstring

    Mine is doing the same, codes are;
    Running codes:
    Memory codes:

    Shop cleaned maf sensor and idle control somthing, sensor? got better but came back an is worse now. started when small hose from the water pump got kinked, now temp gauge barely moves but gets plenty hot. flushed system, no change. so is the pump shot possibly?
    Ideas where to start?

  • Sara Jones

    I have an 01 olds Aurora 4.0…. Idles rough, goes even when kicking into passing gear, no hesitation in acceleration, once I hit 20 mph check engine light starts to flash, when showing down as soon as I’m below 20 check engine light is solid….

  • KlayNorton0178

    Nice blog post . Incidentally , if your company is wanting a NY DTF CT-3 , my friend saw a template document here http://goo.gl/Ii92nI

  • Sonny

    I was getting a P1155 Code on my 2001 Toyota Camry. I replaced the oxygen sensor and now I’m getting P0174 Code saying my system is too lean. Did I purchase a bad oxygen sensor?

  • Glenn

    When I turn my AC on my truck it acts like it wants to cut off and idles badly but when I turn it off it runs fine. What could that be

    • Steve Bryan

      My car does the same thing. Did you fine out what was wrong with yours?

  • Kathy

    My check engine light comes on for a day or two and then goes back off for a day or two. The scan tool is showing a bad o2 sensor, but when when watch the live data the voltage stay in between .1 and .9. At this point, I’m not sure what to do!

  • Steve Bryan

    Will my O2 sensor cause my catalytic converter to go bad or does my catalytic converter going bad cause my O2 sensor to go bad

  • Keta

    I have a 98 expedition xlt I bought as a used vehicle. The previous owner said only the oxygen sensors need to be replaced. The symptoms are mild shaking, Taking a while to accelerate and it seems like it changes gears on it own every once in a while.

  • Jerry

    Hello everyone! I drive a 2006 volks passat. The ‘check engine’ light is showing on the dashboard and there is this disturbing whistle sound that comes from inside the engine after I may have driven for about 30minutes or so. It also stalls acceleration sometimes. The fault code that was diagnosed is P0171. Could this be an 02 sensor issue?

  • Markito King Soler

    I have a 95 Celica S.T 1.8 liter and my car runs well when cold, but shakes like crazy when it warms up. A mechnic checked it and said my upstream o2 is toasted…

  • Jim Miller

    With my truck, it really gets weird. 1991 GMC Jimmy 4×4. Always ran like brand new after replacing bad fuel pump and underhood sensors. Lately when it rains or snows or just high humidity, it sputters, misses, hesitates. diagnostics came up with a code 24 (VSS sensor), but speedo works fine. Cleaned connection to VSS anyway and sealed it with di-electric grease, as its a common problem here in Idaho winters. Anyway. Unhooked the battery to clear the computer, truck runs great until it rains again or is cold and wet out. Then I go through the same routine of the misfires, hesitations , etc. Starts right up when cold and will idle nice all day at 800 RPM. I do however, smell a very rich exhaust, as if the choke is fully closed. O2 sensor???

    • myxolydian-minor

      100% cap,rotor and spark plug wires.spray wd40 on your spark plug wires,cap and rotor next time it does it,if it stops you found your problem.

  • stefan

    Can some 1 help me. Car starts up then cuts out

    • myxolydian-minor

      you need to have your car fixed

  • Anita Miller

    I see that these posts are very old but I’m still hoping that someone will be able to help me.
    I have a 2001 Mitsubishi Montero Sport with two codes coming up, one is p0507 idle air control system RPM higher than expected and the second being p0421 warm up catalyst efficiency below threshold Bank 1. Please could someone tell me what this all means LOL. I need to know exactly what part I’m needing to buy.

  • Robert Blandino

    I have a 2001 Chrysler sebring se 4cylinder 16 valve. when its very cold the car has no power and shakes, when it warms up it runs fine. In the summer time it runs fine. could this be a bad sensor?

  • Andre Fernandez

    i have a 1994 Toyota Camry has rough idle feels like it wants to die when I’m coming to a stop or when i cold start it up it’ll idle perfectly, until warmed needle drops to like 700 rpms and starts shaking like it wants to shut off but it never does it has on me but every time I’m sitting in it idling it really feels like it’s gonna shut up i have no check engine light or anything anybody have this problem?

  • Okc Dave

    The site needs some one who knows their stuff rather than only copy-pasting and ad-libbing information that isn’t true.

    (#3) Defective oxygen sensors will not cause a failure to pass smog due to causing “either low or high CO emissions. There is no failure from low CO emissions and there is no case where failing 02 sensors will cause too low CO. There is no “too low” for CO.

    (#5) sentences don’t start with “and”, but a mere OBDII code checker is only a crude indicator, not at all “the most accurate diagnosis” as it only tells you one generic number, not the parameters read to set the code. Further, there are codes that do not directly indicate O2 sensor when one has failed so it is false that “If your oxygen sensor has failed, the code checker will generate a diagnostic trouble code that specifically indicates your oxygen sensor
    is bad.”

    A code indicating a bad O2 sensor usually means the sensor itself is bad (but not always), but a bad O2 sensor can cause codes that don’t specifically indicate O2 sensor itself.

  • Greg Biggs

    My 2005 Buick LaCrosse runs smooth. I do not hear any exhaust leaks before the downstream O2 sensor. I just replaced the CATALYTIC CONVERTER but the scanner STILL shows a P0420 code. The downstream O2 sensor voltage is pretty steady, but usually below 0.3V but should be above 0.45V. Does that suggest a weak O2 sensor needing replacement?

  • Greg Biggs

    For those who do not already know, you can get a FREE scan from Autozone and many other similar shops. Learn what your codes are telling you.
    Also, most scanners can give you Live Data, including O2 voltages, Short Term and Long Term Fuel Trim and much more. These are VERY usefu!l

  • Andre Kenneth

    My car starts and idles for a few minutes and then shuts off. When I try to restart it, it won’t start. If I let it sit for about ten minutes and try it again, it starts right up but it will shut down again. What could be causing this?

  • Huacho Martin

    hi, my altima coupe 2010 3.5 gives me 15 mpg, i think it is a lot, but have no CEL code and the scanner shows that o2 sensors works right, what could be¿????

  • Jude

    Hello, I have a 2005 Honda Civic Hybrid that I bought off my parents a year ago. It has 75,000 miles on it. It’s starting to idle rough, rattling, and running rich. It just sounds like it’s having a hard time of it when I am at a stop light or a drive thru. The mileage has dropped to 33-35 mpg from the usual 39 to 42. I had the oil changed and the maintenance light came on shortly after. I stopped by autozone yesterday and they checked the codes which indicated the upstream oxygen sensor was defective. Anything else that I should consider before investing in sensors?? Should I have both the upstream and downstream replaced at the same time? Thanks!

  • jehrid bleil

    We have two vehicles with seemingly the same problem. Idle takes a minute to settle down after we start the engine, then when we slow to a near stop the engine will die and we have to start it several times before it stays running. Best Guess?

  • Riana Engelbrecht

    I have had my Corsa Lite (2006) for a year now…..(secondhand of course) As soon as the engine reaches working temp, it starts acting up. It misses, and if it’s in a really “bad” mood it stalls and backfires. Switching the engine off and starting it again sometimes helps . We have replaced the fuel pump, the idle control valve and various sensors, she would be okay for a week and then out of the blue start doing this again. The engine light does not come on, she is not particularly “heavy” on fuel consumption…..and when this starts happening, the rev counter goes up and down. and it seems the problem is worse during summer time……..which gave me the idea it has something to do with the engine temperature……What can I do?

    • Gary Tredinnick

      Hi Riana, The problem sounds like a bad throttle position sensor.

  • Rhynisha Dajon Warsley

    I smell gas coming from the fuel line right by my engine but no leaks what does that mean

  • Maureen Ferraro

    I have a question – my daugher was driving about 65 70 miles hour and had 18 wheeler truck tire hit front of vehicle, slide over hood and smashed her windshield. She had car towed home on Sunday, windshield fixed yesterday. On driving it today, her traction control lighrs and engine light came on – code was for oxygen sensor. She has 90K miles. Are these two lights a coincidence or could they be related to the accident. She says she doesnt remember driving over anything. Thanks.

  • Bob Olivrira

    I have a 2006 dodge charger with a 5.7 hemi. My engine light came on it showed a p0404 code, which is a EGR valve. I replaced it. The engine light came on again. Same code. cleaned the tube and put a new EGR valve on. Two days later, guess what, the light is back on. Has anyone had this problem before.

  • Grizzly Fart

    I have a 1996 Audi A4 Quattro 2.8 manual and I take several cranks to start even if the engine is warm. I drives fine for about 5 minutes and then the engine looses power, usually at a stop light. I went to auto zone and they said it was the o2 sensor. and I don’t know if I should drop $300 on those parts if its not the problem.

  • Alson Ngobeni

    my Audi A4 1.8t 2002 model car can start but cant rev at all. the moment u press the accelerator peadle it doesn’t rev please help

  • Bob Jensen

    2000 Silverado 4×4, 5.3 motor, auto, 165,000 miles. RELIABLE. Driving home, stop and go traffic, stalled and flet like it “ran out of gas” sat for a few minutes, started up but would only run for about 15 seconds and stall. NO check engine lights, NO prior issues, NO indication of problems on any of the gauges. Took it home on a flatbed. Next morning it fired up like normal and ran fine while I turned it around in front of my shop, then stalled. Not even up to operating temp. Anybody have any ideas / experience like this ?

    • Bob O

      Crank Position Sensor Above Starter

  • Colton Johnson

    My car is has codes P0131, P0456, P144A, and P0420. I was told my downstream O2 sensor and purge valve may need to be replaced. My fear is the entire cat converter needs to be replaced, of course I’m told by the dealership that it does. My question is, how can i tell the difference? Difference in repairs in hundreds of dollars.

  • Chuck

    I changed my O2 sensor upstream and I still have bad gas mileage and strong gas like smell

  • WhittakerFamily LawnCare

    What does it mean when bank 1 bank 2 dont read?

  • Deanna Case

    I had an oxygen sensor go out and replaced it failed again and was told there was oil in the line now it continues to fail because of the oil. the mechanic said the oil will eventually go away is this true

  • Leo Lapage

    i have a 2001 chevy 4×4 .and this code po140 keep coming up .and i have change all 4 of the sensor .4 time .i had heard of them going bad .but change them set’s 4 time .and i check the wiring on the plug in .and it good .and i check to see if it had power .and there is power .and it bank 1 sensor 2 that i keep getting the code .i like to know what it my be .and why it keep coming up .5/9/18 7:15 am

  • Derquisha Jones

    My 2009 Toyota Camry is running hirrihor. Just to get it started I have to crank the car over several times for a fee seconds Everytime and when I drive I feel a hesitation and then it gets power and this is every time I press on the has and while sitting an intersection the car will start to loose power and I will have to repeatedly press on the gas just so it doesn’t cut off on me. Then when I drive it cut off while in motion especially when I’m turning onto another street or even up a hill. I had the MAF replaced and the fuel.pump and strainer. Could this be a faulty O2 sensor or catalytic converter??

  • Iammeonly

    My car has been idling rough and there is hesitation when accelerating but now when I crank it it starts to idle then dies after about 3 seconds. I replaced the MAS but that was not the problem.

  • Darkman

    When i turn on the ignition and the fuel needle doesn’t move I know it’s not going to start. I turn off and turn the ignition and the needle gives me a reading, I know the car will start. Is this a bad sensor?

  • Raylin Jones

    My car is having trouble starting. Its not the battery. It clicks but doesnt turn over to start. What could that be?

  • Brandon Marek

    My car makes a small clattering sound when I hit it the gas and a little after I left off could that be an 02 sensor or the whole catylitic converter

  • Andrew Welch

    My bmw 325xi reading says o2 downstream has a 0.395 and a 0.194 upstream reads strong 0.770….. safe to say downstream is bad?

  • Angelynn Carpenter

    Hello, I have a Saturn SL2 96’. Our car wont accelerate past 30 without seeming like it wants to die. We just replaced a new alternator, starter, spark plugs, speedometer sensor and battery still not wanting to operate correctly. So if it is the O2 sensor will the car start to accelerate again and help the speedometer go past 30 mph.

  • Kelly Scott

    I can’t afford both. I don’t know if it’s the upstream or downstream oxygen sensor in my 04 toyota solara.

  • Gil Sprague

    Scan shows the down steam O2 sensor bad, replaced it and have same engine fault light and scan says same sensor bad.

  • Sonia

    My Engine light turned on and to it checked by a computer and comes out that the sensor of my vehicle it’s not working now me using the vehicle in highways which is using my car for a 1 Hour Will it cause my car to turn off in the middle of the road??????

  • Debbie Brasher


  • floyd poplin

    I have a 2010 Chrysler sebring limited with 2.4 engine. My wife was driving down the road when she said that it started acting funny and when she started to accelerate it would not go. I talked to a reputable garage and they said to replace the coils and spark plugs. I have replace the plugs, coils, crankshaft position sensor, MAPP Sensor, catalytic converter and still when you first start it up it runs good, get a 1/4 of a mile from the house, it starts the same thing again and the check engine lights is still flashing, any help from someone?

  • Keith

    I have a 98 Lincoln Mark VIII LSC with a 4.6L DOHC. the Check Engine Light came on after 118,000 miles, I Checked the Code and it was an O2 Sensor. I cleared the Code and continued to drive it to see if it would happen again. About a month went by and I got a Check Engine Light, so I checked it and got the same P0136, an O2 Sensor. So after some study I decided to replace all 4, because if 1 goes the others are probably not far behind.

    I bought Brand New, Brand Name DENSO’s off eBay in the Factory Box, for $72 shipped, and they were $228 at AutoZone, and $109 shipped at Rock Auto.

    The Mark VIII is a very tight fit, but I got them on there, and the car seems to be running beautifully. I noticed the Gas Gauge moves slower, which is always nice.

    With the O2 sensor socket the total cost was $82, to have it done at a shop would’ve cost
    a whopping $300 or more.

    I’ve added ~40 HP to it with just Minor Tuning, and she runs like
    a High Performance Quad-Cam Mustang

  • Kathy Stuart

    I inherited my mothers 2000 Chevy Impala. the gas mileage obviously bad but also you can go down the road and it just cuts off both of the side road and it cuts right back on I’m not sure what the problem is have had that check just the check engine light just started coming on and I said O2 sensors is there anything else that it may be? Im not sure why it’s cutting off, and seems to do it more often.

  • Gina

    Anyone on here after years? Check engine light came n, co2 sensor bad and changed it. Check engine light never went over , even cleared and then unplugged battery. AFTR unplugged battery NOW says:
    P1135 A/F Sensor Heater Circuit Malfunction ( Bank 1 Sensor 1)– no one knows what to do now???????

    2002 Toyota Tacoma 220k miles, 4 cyclinder

  • Ariana Davis

    I have 2001 Honda CivicLx and the check engine light is on I got it checked and it says the 02 sensor came up !! My car shuts off as soon as it gets to the middle of the cool part !! Also my mechanic Notice I don’t have EGR honestly I don’t think I ever had one do you think that can be the reason my car shuts off

  • patricia hollin

    have got 1997 chevy astro miss’s bad in morning when cold.

  • Temeka Cardin

    I just bought a 2015 Chevrolet Sonic when driving it off the lot after purchase miles down the road the water light came on then the check engine light today it is shaking is water and oil in it can you help me