Sorry to say this but your mechanic is wrong. All ?California? 1999-2000 Camry with the 4 Cylinder 5FSE engines have an ?Air/Fuel? (A/F) Sensor. This sensor is mounted in the same location on the exhaust manifold as an Oxygen (O2) Sensor. It looks identical as an O2 Sensor but it should never be mistaken as one. You cannot replace the A/F Sensor with an O2 Sensor because the wiring connection is not the same.
I had some bad experience with these sensors on my 1999 Camry. My car has
90,000 miles on it and had the A/F Sensor replaced 4 times already ? like every 20,000 miles the check-engine light comes on like clockwork and it has always been the A/F sensor. I?m not sure if this is what?s causing my problem, but I think it was from the MTBE gas that they used to sell here in California. Ever since they banned it last year, I?ve now gone 30,000 miles on the current A/F Sensor.
The A/F Sensor are around $200.00 here at this parts store -
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Get it changed and your car should be happy.