Q: Q: Oxygen sensors

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Im buying a car, the guy showed me the check engine light, and the codes that came up in the scanner were O2 sensors. He says he pumped cheap gas ( from mexico ) and that was it. Will cheap gas cause the check engine light come up?

My car has 120000 miles.
My car has an automatic transmission.

The quality of the fuel in the vehicle may possible trigger an O2 sensor to produce false readings, although this is very rare and not normal. As you may know the [oxygen sensors]((https://www.yourmechanic.com/services/oxygen-sensor-replacement) which are part of your emissions system read exhaust gases to determine whether or not the appropriate amount of oxygen is present in the exhaust. Based upon this reading, this information is relayed to the car’s ECU which then makes a determination as to whether or not to add more or less fuel to the engine. When too much or too little oxygen is present, this will cause check engine light to come on. Too much oxygen may be present in the exhaust gas due to things like an exhaust leak, a vacuum leak, a faulty mass air flow sensor (causing a lean fuel condition) or faulty fuel injectors. Too little oxygen may be present in the exhaust gas may be caused by things like a clogged air filter, a failing mass air flow sensor (causing too much fuel to be introduced to the motor), bad fuel injectors or a clogged catalytic converter. When the O2 sensor is not working properly, this will cause false readings to be relayed to the computer causing inaccurate adjustments to be made to the intake and fuel system in your engine.

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