97 E36 convertible with CE light on, runs fine with good milage. Mechanic has reset many times, says if car is started in the morning when it's cold temperature discrepancy or humidity can cause a miss read of the O2 sensor. What are your thoughts and if true which ones should be replaced?

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if the vehicle continues to set an oxygen sensor code there is likely fault with the sensor it is identifying. I would check sensor operation, be sure it is swithcing and the heater circuit is working.

- Nick