Driver Side low beam light not working - replaced lamp & checked fuse

Well, i never saw a reply from the original poster about this issue. But for future reference i have a possible solution. On a 2001 Quest the power flows from the battery to two 15a fuses. one for the right and one for the left side headlights. the fuses control both the high and low beam circuits. check to see if they are good. Also do a voltage reading to see if power is available. after that the power flows through a headlight control unit. im not sure the purpose of this unit since the headlight circuit is pretty basic. After that they flow seperately to each headlight, one wire for low and one for high . do a voltage reading at the headlight bulb connector. the center wire is ground. black wire with white rings. . and finally got to 3 grounds. redundant grounds are not a bad thing. these 3 grounds are all interconnected and are common to all your exterior lighting. so if one headlight is out and not the other, or both headlights are out and not the marker/parking lights, its not the grounds. use this to get the basic picture of the circuit health. if you use these points and your headlight does not work, go to your headlight control unit. test circuit power intput at the pins that feed into the module from the 15a fuses. this will establish if power is going in. and then again on the output side feeding to the headlights. this will establish if power is being lost or diminished in the module assembly. you should find the discrepancy there. you can order this module online. in 2019 they seemed to be going for about 30-40 dollars. or… go to the junk yard, pull one from a vehicle there. cheaper and it help you to learn how to take them out if you have a pick your own part type place in your area. now, if after all this you still have no definitive answer, you will need to start opening up wiring harnesses and digging through wires to look for breaks. Good luck

"Hi @Pam Baker

Here’s an image of the relevant section from the 2005-2006 Nissan Altima Service and repair manual show how to check for no low headlight, one side only.

(click on image to enlarge for better viewing)"