Is It Possible For An O2 Sensor To Work Well When Cold But Then Malfunction When Hot?

Just curious. Any of you ever deal with a faulty O2 sensor before?

I haven’t…but they do fail. And yes they may work fine until heated up.

1 Like

Many times.

The Check Engine light turns on with an O2 sensor code.


1 Like

I dont have any codes yet. 2011 Camry LE 2.5L L4 6 Cylinder.

Then why are you worried about it.

O2 sensors can/do go bad. I’ve only had to replace 1 O2 sensor on all the vehicles we’ve owned…most with well over 300k miles.

Don’t worry about it til it happens. Based on my experience it probably won’t ever happen

@MikeInNH the car is hestitating on acceleration. That cant be good no matter what. Thats why im worried about it.

There could be a dozen reasons why it’s hesitating. But if the O2 sensor is bad the OBD-II system should detect it and display a code.

Get the car checked out from a professional.

1 Like

@MikeInNH Took it in for a diagnosis today.

Diagnosis? “Pending Code” “Lean”

Shop Guess ----> O2 Sensor or Fuel Injector

Take it to a different shop.


@Tester I just threw away $100. How can I avoid throwing away money at the next shop? Mind you this was a highly rated shop on Angie’ List Perhaps im just a fool and dont know how to avoid sharks.

Then you just wasted a $100.

A good shop can tell you what’s wrong.

Not guess.


1 Like

@Tester How do you find a good shop?

Ask family, friends, co-workers, etc…


Yes but no code. Just commanded a rich mixture, like 15 mpg to 27 mpg.

Actually just the opposite. O2 sensors have to heat up before they work. That is why your engine uses a default fuel trim when cold. It’s called open loop. When the engine heats up, it goes into closed loop. Many O2 sensors are heated so they begin to work sooner.

Edit: you paid a diagnostic fee. If they just read the code and made a guess, they ripped you off. You could have had that done for free at most car parts stores, i.e AutoZone. They should have looked up the diagnostic procedure for the code in the factory service manual or all data and followed all the steps. That will, in most cases, narrow down to the actual defect.

If you go to another shop, ask them exactly what they are going to do for their fee. You might also ask the mechanic you just used what he did beside hook up a code reader.

1 Like

@kieth There are no engine codes. I had 2 mechanics check the with scanner. The first mechanic is my friend. He’s got decades under his belt with cars. He did a live read while I drove the car. We parked the vehicle and he showed and explained everything in the reader. But no codes.

The second mechanic is the guy who did my diagnostic today. He seemed shady and only guessed what the problem could be.

So I called another shop today. ASE certified. I told them the diagnostic I paid for failed to nail the problem. I asked this ASE shop if they could diagnose it, I would leave the car with them. But that I dont want to pay for another “I DONT KNOW”

Im not throwing $100 paper airplanes on guesswork. I get it. Car repair is HARD labor, but being honest shouldnt be HARD labor either.

So frustrating

I would trust the mechanic with decades of experience over a ASE certified mechanic with only a couple years experience.

Right now you are concentrating on fuel delivery essentially. How about considering whether or not there could be a vacuum leak?

A vacuum leak below the throttle plate will generally cause a rough idle although that could be subtle.
A vacuum leak above the throttle plate will not be noticeable at idle but could cause a hesitation but so could a leak below the throttle plate.

Best and easiest way to check for a vacuum leak below the plate is with a vacuum gauge. That will not tell you where a leak is; only if one exists.
A vacuum leak also has an effect on the MAF sensor and since air filters are dinked around with quite often it might be a good idea to check the simple stuff like air intake boots, clamps, and PCV hoses.

Might be helpful to look at the fuel trim #s at idle and while driving.

You said in an earlier post that the shop told you there was a pending code. A pending code is a code, it just hasn’t tripped the check engine light yet. A pending code can be used for further trouble shooting the problem.