If the MIL is on for any reason, does that mean the car will run rich for as long as its on, wasting gas? Or is that only if its on for a certain reason?

Derek

 

It can be on for any number of reasons. Read the "ECU Diagnostic Trouble Codes" thread up top and do an ECU check.

 

No, i wanted to know if when its on the fuel is rich and wastes it...

 

what clee is telling you is that the MIL could be on for 50,000 different reasons.. until you find out what it is.. you will not have an answer to your question...

if its the Front 02 sensors.. then your answer will be yes..

 

oh, ok thanks

 

.....I thought whenever the light is on, the engine is gonna run rich, Thats what I thought for some reason..

 

no thats wrong.. the light could be on for anything..

Rear o2 sensor - nothing to do with running rich or hurting performance
speed sensor - nothing to do with running rich or hurting performance..

the most common failure for Maxima's where the MIL light is the Front 02 sensors at about 60,000+ miles.. and the front o2 sensors not working may cause you to run rich.. this maybe where the confusion is.