[reldo]

my check engine light has been popping on and off recently so I checked the codes which came back 77 and 91. The 77 I get but I can't find what 91 is...anyone?

 

[JNCoRacer]

9-1 refers to the right bank (or rear bank) O2 sensor, the one on the firewall side of the y-pipe. Its probably bad. If you want to make sure its the sensor and not the wiring you can swap the front bank and rear bank O2 sensors. If you get a code of 10-1 its the sensor. If you still get the 9-1 sit a problem with the wiring. I know it sounds like a lot of work but I'm 99.9% sure its your sensor. I've had to replace all of them on the Maxima's I've owned.