Q: How would I know if it was my upper or lower oxygen sensor that has gone out?

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How would I know if it is my upper or lower oxygen sensor that has gone bad on a 1997 Pontiac Grand Am I know that my gas mileage went bad sucking a lot of gas and you can smell fuel being burned something like in the air almost like carburetor fluid smell n my ets traction system light says its off even wen the button is on. Idk if its caused by the sensor n wat sensor needs to be changed? Thx

My car has 135000 miles.
My car has an automatic transmission.

Typically if an oxygen sensor is bad, the check engine light would come on and a fault code stored in the engine control unit. There are other ways a technician can verify if oxygen sensors are performing as they should. Connecting a scan tool to the diagnostic port, a technician can observe the sensor readings and see if they are operating in the range that they are supposed to. A number of things can contribute to poor mileage like worn spark plugs or a fuel injector that may be dirty and stuck open or not firing properly. Also, if there is an ETS fault, the vehicle can be running in "limp mode." Limp mode allows the vehicle to run even when there is a fault, but it will not run with the same efficiency and power as it is designed to. Have a certified technician look into the poor fuel mileage to isolate the exact cause.

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