First engine light came on due to missing gas cap. put gas cap on and reset message. after filling up vehicle the engine startied became sluggish. took in and was told oygen sensor was a problem. r

How to Reset the Warning Light Gas Cap That Is Loose or Missing

1. Turn off your vehicle's engine. Push button to unlock the gas cap door, if your vehicle is equipped with a locking gas cap door. ...
2. Step to the gas cap door. Open the door. ...
3. Replace the gas cap. ...
4. Close the gas cap door. ...
5. Use an OBD-II code scanner if the warning light does not disappear.

https://itstillruns.com/reset-gas-cap-loose-missing-7817331.html

https://www.theglobeandmail.com/globe-drive/culture/commuting/the-easiest-way-to-turn-off-your-cars-check-engine-light/article14223025
How to Reset the Warning Light Gas Cap That Is Loose or Missing

1. Turn off your vehicle's engine. Push button to unlock the gas cap door, if your vehicle is equipped with a locking gas cap door. ...
2. Step to the gas cap door. Open the door. ...
3. Replace the gas cap. ...
4. Close the gas cap door. ...
5. Use an OBD-II code scanner if the warning light does not disappear. ...
6. Continue driving the vehicle.

What am I missing? Go to the station and put some gas in the tank. Drive to the auto parts store and buy a cap. This may trigger a check engine light as the computer senses a fuel system leak. Some autoparts stores can read check engine codes, and can reset the light.

I know my barrina when gas cap was missing had check engine light on did diagnostic said o2 sensor as well so got a cap from gas station reset computer now no lights on everything fine had something to do with pressure in tank not right

When last did you service the vehicle ?
did they use the proper fuel ?

Chances are the service time is near where you will need to do a basic service, Plug , plug wires, filters etc. And reset the counter.
the fuel ting is just a coincidence.

Check your gas cap. If it's not on properly, missing or defective it will cause the problem you describe.

the cap most likely set an evap code in the computer have it checked with a scan tool.if the cap is on tight then just clear the code and the light will go out.

Try checking your gas cap for tightness. If it recurs, try to replace the gas cap and see if that corrects it. You can stop by most Autozone's for them to check the vehicles computer codes and on many occasions you'll find that "Check Engine Lights" are due to "Emissions" issues. And many of those can be attributed to loose gas caps.
Good luck, DWtsn

IF YOU GOT GAS ENGINE.PROBLEM COULD BE STOPPED UP FUEL FILTER OR WEAK FUEL PUMP.LOW ENGINE COMPRESSION.BAD SPARK PLUG + WIRES + ROTOR AND CAP ALSO BAD COIL CAUSING WEAK SPARK.IF YOU HAVE DIESEL ENGINE SLUGGISH.PROBLEM COULD BE RESTRICTED AIR FILTER DIESEL.INJECTION PUMP TIMING OUT OF ADJUSTMENT.FAULTY EGR AND EPR VALVES.RESTRICTED EXHAUST SYSTEM STOPPED UP MUFFLER PLUGGED FUEL FILTER.PLUGGED FUEL TANK DUE TO FAULTY FUEL CAP.MISSING PROBLEM COULD BE CAUSED BY DIRTY OR FAULTY INJECTORS. THE INJECTION PUMP TIMING OFF. AIR IN FUEL.OR FUEL RETURN SYSTEM RESTRICTED.STOPPED UP FUEL FILTER.OR USING INCORRECT FUEL OR ITS CONTAMINATED.

Try running some fuel injector or fuel system cleaner through the engine and be certain your gas cap is on tight. While you might have encountered some bad gas on your trip it is likely coincidental , due to running at highway speeds for an extended time. Your check engine light is linked to the fuel air mixture ECU which regulates fuel mixture. If an O2 sensor on the engine or exhaust area is clogged or failing due to leaky catalytic converter, the ECU will attempt to adjust your fuel mixture which will affect your idle.
Have a tech run a readout on the vehicle after cleaning the fuel system. The readout will indicate what caused the check engine light to come on.