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Rear O? sensor on a '98 Camry XLE

I’m a car-repair novice trying to get my car to pass its emmissions test. I already replaced my front O? sensor when the auto parts store incorrectly told me that bank 1, sensor 1 was the front sensor. Now I actually have what should be the correct part, but I’m not sure where the rear sensor is/the best way to get to it. If anyone could type me through it, I would really appreciate it!

You need to stop blindly changing parts. Most sensors can be tested to verify good/bad.

Does the check engine light come on? If so, you need to get the error code scanned off the computer and post it here. It will look like P0123.

In what way does your car fail emissions? What are the limits in your state for HC, CO and NOx and what is your car putting out.

Circuitsmith is right about not accepting diagnostic codes at face value. Generally not a good idea.

However O2 sensors look to be something of an exception. Most diagnostic codes could have many causes other than the obvious, but diagnostic codes that specifically refer to O2 sensors really are caused by either the O2 sensor or the computer/computer programming. Odds are that your O2 sensor really is bad or terminally ill assuming that the computer didn’t just set the code in order to liven up an otherwise dull afternoon. You might try clearing the code and seeing if it comes back.

The converse is not true BTW. Failing O2 sensors that haven’t completely died can easily cause problems to be reported elsewhere in the powertrain.

Anyway, if your Camry is like my 1999 4 cylinder, the downstream O2 sensor is in the exhaust pipe one connection to the rear of the catalytic converter. Pretty much under the shift lever. I could be off by a foot or two about exactly where it is. I’d go out and check that, but it’s really wet outside. It’ll be the only sensor in the exhaust pipe after the catalytic converter.

I should have made it clear that I assume that if you knew enough to go after bank 1, sensor 1, you must have had a code read out that said it was defective in one way or another.

Even experienced mechanics need to have the repair manual AND follow it. A good mechanic is NOT the one who never refers to the manual.
The B1S1 (bank one, sensor one) is, indeed, the sensor in front of the catalytic converter.
Some 1998 Camrys use Wide Band Oxygen Sensors. You must replace with the same. Look at the emissions label under the hood. If it says the car complies with California emissions, it will take the wide band oxygen sensor (at least, on the front S1B1). If it says Federal emissions, tell your parts supplier that.
Troubleshooting always goes before parts replacement. Oxygen sensors are caused to go bad by what happens in the engine (too rich, burning oil or antifreeze,etc.). If you just replace parts, those things which are at fault will cause the new part to go bad.
4 cylinders? 6 cylinders?
Some repair instructions Go there and register (easy). Come back here, and click on the link again.

I just have the paperwork from the mechanic. It failed on code P0135 with the description “O? Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)”

I just dealt with AutoZone for essentially the same issue. I found that their information on the codes for my 2000 Camry V6 are WRONG as they relate to the O2 sensors. Fortunately, I have the factory manuals which point to the correct sensor.
Hellokit is correct about the difference in the type of O2 sensors. My California Camry V6 takes an Air/Fuel ratio sensor. The federal version takes an O2 sensor. I went to the dealer to get the correct sensor the first time because I don’t trust AutoZone to get it right since the sensors look identical.