Code 77

[image12]

Code 77 - Rear o2 sensor

I get a code 77 that comes up randomly while driving. If I clear it, I drive for awhile and sometimes it throw a code 77 and sometimes it wont. If my o2 sensor was bad it would throw a code right away am I correct?

[yoinkAzenki]

yes your rear o2 sensor may be bad. you can either replace it to get rid of the check engine light or just let it be. the rear o2 sensor is for diagnostic purposes only and does not effect your engine.

[image12]

I also read that it could be the cat? I was thinking if the o2 sensor is bad the code would come up soon after I start the car, not randomly throwing a code...

[cotbu]

If you have a test pipe this is common. the r-02 sends the signal to the ecu if theres no difference in a/f from the f-02 you get a code. You also get a code if it's faulty.

You are correct about the cat.

[image12]

well the car just passed smog which is confusing me.