I was driving today and the check engine light came up so I went to autozone to find out what it was. they said it was a P0139, the response time for oxygen sensor 2 in bank 1 was too slow during testing. What should I do now? is it serious? and should I get it fixed?

Thanks

 

Do you have a CEL fix on your car? This code may be a result of said fix. If your car is stock and you are getting this code, and you're still under warranty, have a dealer look at it.

 

Don't people use a resistor as a CEL fix?

 

For the EGT probe in the uppipe, yes. For a catless downpipe it's more complicated than that. There are electrical fixes that get connected to the rear 02 sensor circuit, and these can sometimes cause rear-02 sensor related codes. An alternative is the "mechanical fix" which consists of two readily available spark plug anti-foulers installed as spacers under the sensor.