I have a 1991 Camry V6 with 130K miles. For the last few winters my check engine light has come on when the car starts and the temp is 40 or below. If I let it run a minute or two, then turn it off and restart, the light goes out. I checked the codes and they point to the oxygen sensor.
During the winter months my gas mileage goes down to about 19.5. When spring arrives and they gas companies change the formula the check engine light no longer appears and my mileage goes up to about 25.
I’m thinking its the O2 sensor but I don’t see it on the front exhaust manifold. (That would be too easy) Is this something that I could do without taking off a lot of other parts? Does this engine have only one sensor?
Rich, if you are still having this problem, this winter, find a way to have the trouble codes read. Bring the code here and we’ll see what bright ideas we can come up with.
PS, If you were to get a repair manual, that would be so helpful.
This is an ODB-I car. These DTCs are not as helpful and notoriously vague. Toyota recommends changing these O2 sensors every 50K miles. They are not expensive, less than $50 at the dealer. This car only has one, down where the exhaust from both banks merge together before the catalytic converter. It should be easy to get to from underneath, but you will need a special O2 socket with a cut on the side for the wire, or a 22mm box-end wrench (7/8" equivalent) if you have room to swing it.
I do recommend the Toyota replacement at the dealer. Every Toyota I’ve worked on are picky about these sensors, and many aftermarket O2 sensors don’t seem to work.
Hi, BK!
Thank you very much for the reply. I didn’t think to look underneath, thinking it would be on the top manifold or upper pipe someplace. I’m off for the next two weeks so it’s going to be my Christmas project. I’ll let you know how it turns out. If I can get the old one off I will purchase a new one from the dealer. My mileage has dropped to 18 mpg, just 1 better than my V-8 4Runner. With a 50 mile round trip commute I’d really like to have that 24 mpg back.
Rich
I pulled the old one out and took it to a Toyota dealership. They needed my VIN also. Fortunately, this car had been serviced there so they had it on file. They said there are many different types of oxygen sensors for each vehicle year. The cost is $162 and they have to order it for me.
On this one, there is a 12mm bolt on each side of the sensor. There is enough room for me to get a ratchet and stubby extension in there. The bolts came off easily and the sensor came out with no effort. The wire is short and the connector is hard to get to from the bottom so I pushed everything up to the top of the engine and was able to disconnect it from the plug up there. It was much easier to remove than I thought.
Hellokit, sorry I missed your post the first time. A repair shop said my codes (I think they were 52 and 57) related to the oxygen sensor and that if it wasn’t working it would retard the spark to prevent knock and my mileage would go down, which is what was happening. There was another code that was more serious but he said it would take more investigation. My mileage continued to drop, now at 18. With BK’s posted information I was able to find the sensor and remove it. I’ve ordered the replacement and I hope it fixes the problem or I’m out $162 and my wife isn’t happy about leaving her van in the cold 
New sensor installed without any issues. The sensor came with a new gasket and there were no issues with taking off the old one and putting on the new one since there isn’t any kind of sealer on it.
Took it for a spin and it definitely has more power now than before. No cold weather for a while so I can’t test that out but with the improved performance the mileage should go back up to 24 or 25 again.