Lowbeams on Mpv went out. Highbeams ok, but

You can't use High Beams as dipped, the spread is different. Just go to another garage, it can only be the bulbs, the connection, the fuses or the relay. In fact you can check all those yourself! It appears to be a known issue on the Impala. Look at the videos

https://www.google.com/search?q=2000+chevy+impala+headlight+problem

Fuse Box Diagram Chevrolet Impala (2000-2005)

https://fuse-box.info > chevrolet > chevrolet-impala-20...
It is located on the passenger's side of the instrument panel, behind the cover. The location of the fuses in the passenger compartment: Chevrolet Impala (2000- ...

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Hi Daniel, Replace the hi beam relay.......CHEERS..

For the low beam problem, Swap relays 45 & 46 in the underhood fuse panel. Relay 46 is for the Low Beams. If that fixes the light, replace the relay that cam out of position 46.
Since the high mounted brake light is working, that indicates that the brake switch is good. You need to check the bulbs in the rear tail light assembly, if they are good, check fuse #34.

The dark blue wire is the ground wire for the low beams and your pink is the ground for the high beams.

When you touch that wire to ground the lights should come on. If not there is a short/break in the wire somewhere

Double check your pink wire to confirm that it is supposed to be a ground signal.

Yes, the low beams will shut off if you turn on high beam. Not sure which way yours work but if you push the lever for high beam, pull the lever back and all lights will come on or vise versa. You would think all the lights would turn on when going into high beam.

If your highbeams are working fine, you must be referring to your low beams not working I would simply check the 2 bulbs and make sure the low beam filament is good, theres a strong possibility that your BOTH low beam filaments are bad and require replacement of both headlight bulbs to get them working again its a very simple repair.....

Sounds like a faulty high/low beam switch.

You need a new headlight dimmer switch located on the steering column between the dash and the firewall

replace the bulb, highbeam and lowbeam use different filaments (on the same bulb) and lowbeam get used much more hence blow first 99% of the time leaving only a working set of highbeams

try replacing the fuse because low beam and high beam are two different systems