Low Beams not working.
Have daytime running lights during the day and high beams at night. When the sensor turns on the headlights there are no low beams, only highs work. Have replaced the dimmer switch and did not correct problem. Also have checked the relay and fuses which are working?
Find the Brain Box..unplug,replug. It worked for me.. could be bad connection.?
suspect the headlight toggle in the turn signal....the reason is this one sees a lot of activity...is fairly high-amperage and subject to degridation~ https://www.google.com/#q=2009+GMC+Sierra+1500+headlight+switch&tb m=shop&spd=9005417846704392573
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