Low beams only work sometimes

Your best bet , take your vehicle to a qualified repair shop . Before you want to replace the BCM . . Professional tech would check for DTC'S - diagnostic trouble code's in the BCM before replacing part's that are not needed .

No signal at signal wire on relay ???? Which circuit wire mite that be ? Hooking up a factory or professional scan tool to view input data from the switch would also be a good step .

Headlamps
The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC, the headlamps will be OFF in daylight conditions, or low beam operation in low light conditions. Battery positive voltage is supplied to the low beam relay and the high beam relay in the underhood fuse block. When low beam headlamps are requested, the body control module (BCM) supplies ground to the coil side of the low beam relay. This activates the relay and the relay supplies voltage to the left hand low beam headlamp through the LH LOW BEAM fuse and to the right hand low beam headlamp through the RH LOW BEAM fuse. Ground for the left hand low beam headlamp is provided at G101. Ground for the right hand low beam headlamp is provided at G102. When high beam headlamps are requested, the body control module (BCM) supplies ground to the coil side of the high beam relay. This activates the relay and the relay supplies voltage to the left hand high beam headlamp through the LH HIGH BEAM fuse and to the right hand high beam headlamp through the RH HIGH BEAM fuse. Ground for the left hand high beam headlamp is provided at G101. Ground for the right hand high beam headlamp is provided at G102.

Headlamps Inoperative - Low Beams
Step
Action
Yes
No
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference: Master Electrical Component List
1
Did you perform the Diagnostic System Check - Vehicle?
YES - Go to Step 2
NO - Go to Diagnostic System Check - Vehicle
2
Place the headlamp switch in the HEADLAMP position.
Place the headlamp dimmer switch in the LOW position.
Do the low beam headlamps illuminate?
YES - Go to Testing for Intermittent Conditions and Poor Connections
NO - Go to Step 3
3
Disconnect the turn/headlamp switch connector C2.
Connect a 15-amp fused jumper between the headlamp low beam signal circuit and a good ground.
Do the low beam headlamps illuminate?
YES - Go to Step 4
NO - Go to Step 5
4
Inspect for poor connections at the harness connector of the turn/headlamp switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
YES - Go to Step 7
NO - Go to Step 6
5
Repair an open or high resistance in the headlamp low beam signal circuit. Refer to Circuit Testing and Wiring Repairs .
YES - Did you complete the repair?
NO - Go to Step 7
--
6
Replace the turn/headlamp switch. Refer to Turn Signal Multifunction Switch Replacement .
YES - Did you complete the replacement?
NO - Go to Step 7
--
7
Operate the system in order to verify the repair.
Did you correct the condition?
YES - System OK
No - Go to Step 2

It's more then likely the dimmer switch .

DTC B2575
Circuit Description
The body control module (BCM) turns on the LOW BEAM relay when the ambient light sensor senses a dark condition or the low beam headlamps are requested ON. Battery positive voltage is supplied to the LOW BEAM relay at all times. The BCM grounds the LOW BEAM relay control circuit in order to activate the relay.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2575 Headlamp Control Circuit

B2575.01
Will set if there is a short to voltage in the low beam relay control circuit.
B2575.06
Will set if there is an open or short to ground in the low beam relay control circuit.

The headlamps are controlled by the BCM - body control module , do you know what that is ? The headlamp switch is a input to the BCM ,the BCM energizes relays to turn on the headlmps , low beam relay , high beam relay , DRL relay . These relay's are PCB - printed circuit board relay's ( non - serviceable ) If found to be bad the whole under hood fuse box would need to be replaced .
Low Beam Headlamp Operation
The low beam headlamps may be turned ON in 3 different ways:
• When the headlamp switch in the HEAD position for normal operations
• When the headlamp switch is in the AUTO position, for automatic lamp control (ALC)
• When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay
Battery voltage is applied at all times to the coil and switch sides of the LOW BEAM PCB Relay located in the underhood fuse block. When the headlamp switch is placed in the HEAD position, ground from G202 is applied through headlamps ON switch signal circuit to the body control module (BCM), signaling the headlamps ON request. In response to this signal, the BCM applies ground through the headlamp low beam relay control circuit energizing the low beam relay. With the relay energized, battery voltage is applied through the switch side of the relay, the left and right low beam fuses, and the low beam supply voltage circuits illuminating the low beam headlamps. Ground for the left headlamp is provided at G101 and the right headlamp at G100.

Do you know what B codes are ? BCM - DTC'S - diagnostic trouble codes , need a factory scanner or professional one to view these codes , not autozone or advance etc....Having a qualified repair shop check your vehicle would be your best bet.

DTC B2575 00: Headlamp Control Circuit

Circuit/System Description
The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is Auto, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The Off portion of the headlamp switch is a momentary switch which overrides the automatic headlamps and will turn off the vehicle headlamps. When in the Off position, the headlamp switch grounds the headlamp switch headlamps off signal circuit, prompting the BCM to turn off the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Headlamp position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.
The headlamp high beams are controlled through the flash to pass switch and the headlamp dimmer switch, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The headlamp dimmer switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.
The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit. This energizes the coil in the LOW BEAM PCB relay, causing the relay switch to close. This then applies B+ to both low beam headlamps through the LT LO BEAM and RT LO BEAM fuses, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the HIGH BEAM PCB relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the LT HI BEAM and RT HI BEAM fuses, illuminating the high beam headlamps

seems like the multi-function switch is failing
easy to replace and fairly common

Hello, is sounds like your issues are coming from within your turn signal/high-low beam switch. Most of the time the wires get worn or break and start rubbing around on each other causing troubles within the electrical circuit. Other times the contact switches inside the turn signal/high beam switch/lever wear and loose contact over time. You may be able to see wires leading from switch into steering colum. Check for bad wires, if none you may have to replace switch which you can get from any junkyard for bout 5 bucks plus learn how to take it apart in a junk car no one is worried about getting destroyed. BE CAREFULL WITH AIRBAGS when you pull your steering wheel to fix switch. It is not a difficult job to do.

It sounds like you are confused about how your headlamp system is supposed to work. The DRL does not run on the High beam circuit, it runs on the low beam circuit. The fog lamps are supposed operate with the park lamps and also with the low beams, not the high beams. From your description, I would say that your system is operating as designed and you are having trouble telling High from Low. (Don't feel bad, that is why high beam indicators were invented in the first place.)

Your headlight switch has overheated and failed. It's common. The switch is $158 new and replacement requires airbag and steering wheel removal.

just replace the dimmer switch under the column its wore out on the low beam side

DID YOU CHECK THE BULBS?

its probally the bulb........alot of car headlights are DUAL element meaning one bulb has 2 little elements inside one for low beam one for high beam...............Most times the low beam burns out because its used more.....get it one bulb gives both high and low beams.......REPLACE bulb......if you don't know what kind go to auto part store, tell them the make of your car and they will give you the right one .....

the head lights have tree wires goig to it one groun one gets power when high beams on the 3rd gets power only with low beam on test the wires or try by plugin a good known head light to conector if it works with low beam then replace both head ligts because head light come with two bulbs in one high and low