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Oxygen Sensors

I’m about to pay for the replacement of the third oxygen sensor to go bad in my 2000 Toyota Tundra. These malfunctioning sensors have been the only reason my Check Engine light has ever come on since I’ve owned the truck. My question is whether its necessary or worth it to replace these sensors since they never seem to really indicate a problem with the engine, only a problem with what is supposed to detect problems. The seven hundred bucks I will have spent on these little gems is starting to feel like Toyota’s version of a Maytag repairman’s employment security plan.

You probably could have had the sensors replaced for much less by an independent mechanic.

If the sensors are faulty, the engine management computer will get false information which can lead to increased fuel use, more pollution, and poor engine performance.

If a sensor is bad, replace it. You don’t have to pay Toyota prices, however.

Whcih sensor is it? The after-cat one or one of the before cat sensors? Is it the same sensor everytime, or are they just slowly replacing them one-at-a-time as they go?

Info is missing.
I assume it’s not the same sensor being replaced, but different ones each time?
How well do you keep up maintenance? Old spark plugs or anything else causing a slight misfire can affect O2s over time.
Any loss of engine coolant? Coolant leakage from a weeping head gasket can ruin O2s.

I have discovered that instead of replacing the Oxygen sensors with the $300 ones that you can vuy at the Toyota dealer, you can buy universal Oxygen sensors at Auto Zone for less than $100 each. This might not address what is causing them to fail, but it will save you money if you have to keep replacing them.

It’s (usually) NOT a malfunctioning oxygen sensor which causes the check engine light to come on; but, a condition which the oxygen sensor is REPORTING to the engine computer. If the engine is running too rich, or too lean, or is misfiring, the oxygen sensor informs the engine computer. In response, the engine computer decides if it turns on the check engine light, or not. What is the DTC (Diagnostic Trouble Code) when the check engine light comes on?

If you want to know what kills O2 sensors, here’s some interesting reading.


One thing that puzzles me a bit after being on the board a long time is the huge number of O2 complaints.

Me, and all of my family members, have always put a lot of miles on cars but maintain them very well. With one exception, not one of us has ever needed an 02 on any car at all.
The one exception, not the O2’s fault, was on my old Mercury Sable in which I was doing some basic maintenance servicing and a wrench slipped on a stubborn bolt. The wrench went sailing, and as luck would have it, bounced off the O2 and cracked the porcelain.
Other than that one case, never a problem with any of them.

Until some moron took out my son’s Camaro the other night he had almost 300k on the original O2 with zero problems.

I too have a Toyota. A 1999 Camry (automatic) and I’m at about 191k miles. My check engine line started coming on (and off) about a year ago. It would come on for 3 days, then shut off for a month and continued, off and on. Once it started lasting more then 3 days, I took it to the Precision Auto-Tune down the street. They told me it was one of my O2 sensors. (They did not tell me the code and obviously couldn’t tell me which sensor). After a little ticket shock, the feeling that the mechanics would be doing exploratory surgery and the light turning off on its own I decided to leave it be. The light didn’t bother me till it started staying on longer and I started noticing a change in shifting (and now gas economy) recently. I did purchase a U380 OBDII Check Engine Auto Scanner Trouble Code Reader and I’m getting the code PO171 (too lean), which reinforced the O2 sensor but also the exploratory surgery feeling.
Is there anything else this could be besides the O2 sensor? Also, if it is an O2 sensor, will it be a crap-shoot which one it is (or both)?

@ tester - linky no worky for me

JayLynne, the post you responded to (this thread) was almost 4 years old.

Your best bet is to start your own new thread.

I suspect that many 0² sensors are replaced because they are doing what they are designed to do, report when there is a problem, which is not the same as reporting that the sensor is bad.

I’m with OK…I’ve only had ONE O2 replaced EVER…And that was because the guy who did my exhaust…had to remove the O2 sensor…and didn’t tighten it on properly…and 2 miles down the road it popped out…Drove back…he knew immediately what happened…had a new O2 sensor delivered in 15 minutes and put it in…And that’s it…Total mileage on all vehicles combined with this one and only replacement is over 1 million miles.

PO171 could be a vacuum leak or a dirty MAF sensor.
On a 13 year old car rubber hoses or gaskets can get iffy.
The thing to do next is to look at the signal from the O2 sensor with a graphing scanner or oscilloscope.


That link is four years old! Who knows what that website has changed since I posted that link.


Thanks all of replying to this post! It definitely gave me a cheaper alternative to check first (instead of replacing the O2 sensor). I really appreciate it!