My 2004 century worked completely until yesterday when i arrived home and turned off the headlights,the next day i go hit the remote to open the car locks and i only see the blinker lights and parking lights on(whenever i did this the low beams would come on to),so i got inside turned the dimmer on and only the side lamps and blinker lights come on,the low beams dont but the highbeams do work,both low beams dont work in both scenerios when i hit the beeper or turn them on manually.I checked every fuse and relay and they all work.What is the issue?
I found this. It seems a bad headlight driver module are common on GM.
The headlamp driver module (HDM) is an electronic module that provides electrical power to the vehicle low beam headlamps. The HDM is controlled by a pulse width modulated (PWM) ground signal from the body control module (BCM). The BCM determines the desired lamp intensity using the ambient light sensor, multifunction switch and the park brake switch as inputs. In general, the HDM will operate in 1 of 3 modes:
• Reduced Intensity Mode: This mode is used by features that do not require or allow maximum low beam headlamp intensity such as daytime running lights (DRL) (nominal: 85% duty cycle).
• Full Intensity Mode: This mode is used by features that require full low beam headlamp intensity such as low beam headlamp operation in manual or auto modes (nominal: 100% duty cycle).
• Off Mode: This is the default mode of the system that will occur when none of the features described above are active. The BCM will deactivate its PWM output (0% duty cycle) during this mode.
You probably need a new headlamp driver module (HDM), common problem on GM vehicles.
hooking up a scan tool an checking for codes in the BCM would be the first thing to check
DTC B3802
Circuit Description
The body control module (BCM) monitors the park lamp switch signal circuit and the headlamp switch headlamps on signal circuit in order to determine when the park lamps and headlamps should be illuminated. When the headlamp switch is turned to PARK, the BCM senses that the park lamp switch signal circuit is grounded and the headlamps switch headlamps on signal circuit is open. The BCM will then energize the park lamp relay illuminating the park lamps. When the headlamp switch is turned to HEAD, the BCM senses that the park lamp switch signal circuit and the headlamp switch headlamps on signal circuit are grounded. The BCM will then energize the park lamp relay and headlamp driver module (HDM) illuminating the park lamps and headlamps.
DTC B2575
Circuit Description
When the BCM receives a ground signal from the headlamp switch requesting the low beam headlamps, the BCM will energize the HDM low beam relay by grounding the low beam relay control circuit.
As WW mentioned, that is a possibility…
But did you check the bulbs?? or to even see if the socket has power to them??
I have had both low beams go out at the same time more than once over the years…
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OP, your car’s lighting system , including the headlights, is computer controlled. Not nearly as simple, compared to days of yore when the lights were powered up by a manually operated switch which connected battery power directly to the bulb. Your car, and most newer cars, you still press button, but a computer senses the button press, then the computer turns the bulb on using circuity on its circuit board. Or, to make it even more complicated, the button sensing computer may send a digital code to another computer, and that computer turns the bulb on.
So you’ll probably need a shop with the needed knowledge, experience, & computer tools to figure this problem out for you. If you want further help here, suggest to post a wiring diagram of the pertinent circuitry. About the only thing a inexpert car-owning diy’er could do in this situation is verify the light fixture ground wire has a good connection to chassis ground.
People frequently do not notice when one low beam goes out, nut they do when the second one blows.
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Thx,i new it would be something simple,all i did was connect a mini led bulb to the connector of the low beam bulb and it turned on,so the issue is that both bulbs where blown,but thankfully that was the problem and not some indoor electrical issue.
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Did the bulb connectors look okay?
They weren’t blackened or melted?
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Good for you for getting to the bottom of the problem. I check light bulbs by disconnecting the connector & measuring their filament resistance. A faulty bulb measures as an open circuit.
Ok do i replaced the bulbs and still nothing,when i connect a wire to the connectors it gives power but then stops,could this be the multi-function switch?
I’m not sure what you mean. If you are saying you measure the proper voltage at the harness side of the connector, but when you plug the connector into the light fixture the known-good bulbs don’t light, the most likely cause is a bad connection at that connector. A fairly common problem. Gadgets called “pigtails” are usually available which make it a fairly easy job to effect a repair. Just cut the old connector off of the wiring harness, and connect a new connector (the pigtail) on. You’ll have to have some knowledge of how to make the connections properly.
Other possibilities though, the multifunction switch for example. So suggest to ask a shop to do a diagnosis. Then you can fix it yourself if you like.
The headlight connectors are powered by the fuse, always on, not switched.
The ground for the bulbs is controlled by the multi-function switch and headlight switch. Connect a bulb to the socket, if you have power on both wires for that bulb, there is no ground from the multi-function switch.
Have you checked power AND ground?
So i replaced the multifunction switch and that fixed it so I think you were correct
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Congratulations! 
Did you arrive at the bad multifunction switch through testing, such as using a testlight and/or multimeter?