Left headlight low beam stopped working. High beam works ok. Low beam bulb changed but still not working. Checked fuses in engine compartment but couldn't see any blown.

I've checked the wiring diagram for your vehicle and the fuses are in the under hood fuse and relay center located on the left side of the engine compartment, the interior fuse block is on the left of the steering wheel However I think your problem is bulbs what happens is that one low beam burns out and you don't notice so when the other goes out it appears they both went out at the same time. The same fuse powers high and low beam so if the high beams work the fuses are good. I hope this helps. Take care.

Sounds like a switch issue.

Check for power with a test light with the light connected. If you have power then its the ground. If no power then you will need to trace the wire back to find break. As I recall they did have seperate fuse for left and right headlight high & low beam. Also did you get a defective new bulb?

1. I own a Protege and once the low beam bulb burns on one headlight the car electronics quickly cook the bulb on the other headlight as well. it is a poor design by the mfr. Pull both bulbs to make sure the low beam is not cooked.

High beam switch moat likely, have you checked relays and fuses?

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.

Issue is more than likely the connection with the bulb

For Audi A4 the fuse box is located on the left side of dashboard behind a plastic cover (for left hand steering wheel vehicle). On inner face of the plastic cover you will find the fuse diagram.
First fuse on first row from left upper corner is Fuse Nr.20 = F20 (15A) - RH headlamp low beam, headlamp adjustment.
First fuse on second row from left upper corner is Fuse Nr.21 = F21 (15A) - LH headlamp low beam, headlamp adjustment.

Check the fuse. There are seperate fuses for right and left. You dont mention if the high beam works for that side? If it does, the fuse is good. The GREEN wire at the bulb is the ground for the low beam. If that wire has power, then the ground is bad. If the high beam works, the hi'lo beam switch is good, and there is a problem between that headlight and the Engine Compartment Junction Block

do your flash to pass lamps light when you pull the stalk towards you? If yes, the bulbs are ok.
Do the hig beams work?
Your headlamps have sepaerate fuses for each headlamp and you have a low beam relay and a high beam relay under the hood in the black box.
If everything is out, I suspect a bad headlamp switch.
Check car-part.com and look on page with * for cheapest price.

Your owner manual will identify fuses & relays.

PS, You did not recently instal high current bulbs did you? If yes, put originals back in.

HEADLAMPS

The voltage is supplied to the lamp switch through a fuse. This fuse is located in the central junction box in the left-hand footwell.
When the headlamps are switched on, a voltage is supplied to the high beam/low beam switch and to the low beam relay. The relay for the low beam is located in the battery junction box (BJB) in the engine compartment.
If the high beam/low beam switch is set to "low beam", then a voltage is supplied through the low beam relay to the low beam part of the headlamp assembly. The left and right-hand low beams are fused separately. The fuses are located in the battery junction box (BJB) in the engine compartment.
If the high beam/low beam switch is set to "high beam", then a voltage is supplied through the high beam relay to the high beam part of the headlamp assembly. The left and right-hand high beams are fused separately. The fuses are located in the battery junction box (BJB) in the engine compartment.

----------------------------------------------------------------------------------------------------------
Lamp Switch
Removal

1. CAUTION: Disconnect the battery ground cable. For additional information, refer to Section 414-01 .
   Remove the lower driver's side footwell trim.

1. Detach the lamp switch bezel.
   • Remove two screws.

1. Remove the light switch.
   • Remove three screws.
• Disconnect the electrical connector