Can O2 sensor go bad w/o CEL or code

[jroros]

I have a 2002 Camry w/2.4L 4cyl and 140k miles. Recently the mpg dropped to under 25mpg combined hwy and city. It used to be about 28mpg. I was wondering if the O2 sensor could be bad even though it has not thrown any codes and no CEL.

Also the MPG computer says it is getting 29mpg, but I'm not anywhere near that. I calc the mpg for every tankful using the trip odometer and it came in under 25mpg.

[gdanaher]

Sensors degrade over time. If never replaced it is likely near the end of its life cycle. It may not have degraded to the point of failing, but is likely due for replacement. You really don't want to just throw money at it though. Other things could cause decreased performance including under inflated tires, dirty air flow sensor, worn plugs, dirty air filter. See if you can get a tailpipe analysis and that will give you an idea if the exhaust is dirty and lead to a better decision regarding the repairs.

[JohnGD]

Yes, they can go bad without setting the MIL. Some P0420 Catalytic Converter Efficiency Below Threshold codes were set because of it, while the tailpipes were "blowing zeros", according to a Motor.com article.

The thing is, late model PZEV vehicles these are supposed to be warrantied for 10yr/150K miles?? But if it doesn't set a code I guess you'd have to prove it's bad.

Computer can be off because vehicle speed sensor can be off. But that means you should be 1 or 2 MPGs off from manual calculations. Otherwise the computer just stinks.

Originally Posted by jroros

I have a 2002 Camry w/2.4L 4cyl and 140k miles. Recently the mpg dropped to under 25mpg combined hwy and city. It used to be about 28mpg. I was wondering if the O2 sensor could be bad even though it has not thrown any codes and no CEL.

Also the MPG computer says it is getting 29mpg, but I'm not anywhere near that. I calc the mpg for every tankful using the trip odometer and it came in under 25mpg.

[MR2Jedi]

Yes they can. I ran pig rich until I figured it out.

[jroros]

Originally Posted by gdanaher

Sensors degrade over time. If never replaced it is likely near the end of its life cycle. It may not have degraded to the point of failing, but is likely due for replacement. You really don't want to just throw money at it though. Other things could cause decreased performance including under inflated tires, dirty air flow sensor, worn plugs, dirty air filter. See if you can get a tailpipe analysis and that will give you an idea if the exhaust is dirty and lead to a better decision regarding the repairs.

The air filter was dirty so I replaced it. The plugs were replaced at 100k, tires are ok. How do you clean a dirty air flow sensor. Where is it located.

[jroros]

Originally Posted by MR2Jedi

Yes they can. I ran pig rich until I figured it out.

How did you know which O2 sensor to replace.