Low beam drivers side doesn't light; high beam does; changing bulb does NOT fix the problem: toyota echo 01

Check the wiring on that light. Also check the bulb with a couple of wires to the battery, or swap the bulb left to right to make sure the new bulb is okay.

Twist out and disconnect wires. Replace, twist in.

This is usually caused by a failed front control module as this unit controls the lighting on the vehicle!
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These trucks are known for bad multifuction switches.
the switch that i talk of is the signal switch , the handle is the switch, it bolts to side of steering column . this switch controls the signals and the headlights and high /low beams. the other thing is the headlight switch connector, the connector some times goes bad and starts to melt or just comes out of the connector. you will need to remove the cover to steering column, the screws are located under the bottom cover in holes. remove cover and check connector and then test for power if you have power going into switch but not coming out then switch is bad.

the last thing is to make sure the bulbs are good , make sure the headlight bulbs are good , and also the driving light bulbs, test for power at the connectors to those lights to.
You will need to do a little testing to find the problem.

On a 2008 Prius, If both High beams work but only one side has working low beams, then it is most likely a fuse. So before breaking your knuckles to change the bulb, check the fuse first. I found out the hard way as my mom distressed to me that her drivers side headlights were out. So without checking to see if low and high were working, I proceeded to remove and replace the bulb - ouch! There are 4 10 amp fuses that protect the circuits for low/high beam function. They are under the hood in the fuse box on the drivers side and they are marked on the box cover. Check them before changing the bulb.

I would check for voltage at the dimmer switch first.

there should be separate relays for your headlights inside the fuse panel under the hood drivers side fender

Change the bulb. It's a high/low bulb, and the low side is burnt out.

I assume you have changed the bulb?

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.