2006 chevy malibu no signal at relay for low beam lights. Switch is good

Low Beam
Voltage to the headlamp switch is available at all times from the HDLP SW fuse 7 through CKT 1940 (ORN). When the headlamp switch is turned to the HDLP position, the headlamp power relay coil is energized through CKT 352 (WHT). A signal is also sent to the body control module (BCM) that the headlamp switch is ON. When the headlamp switch is in the AUTO or PARK position, the ambient light sensor (located in the right speaker grill) senses either daylight or darkness and sends the signal to the BCM. When the Ambient Light Sensor detects a dark condition, the BCM produces a signal that will energize the headlamp power relay through CKT 352. The relay coil is grounded through terminal F7 connector 2 of the underhood fuse block to CKT 350 (BLK) to G102. When the headlamp power relay is energized the relay supplies power to the LT HDLP and RT HDLP fuses. The RH low beam headlamp receives current through CKT 198 (DK BLU) from the RT HDLP fuse. The LH low beam headlamp receives current through CKT 712 (YEL/BLK) from the LT HDLP fuse. Both headlamp low beam bulbs are grounded by CKT 525 (YEL) through the underhood fuse block to the multifunction switch (low position) contacts through CKT 10 (YEL) to the headlamp grounding relay in the body relay block through the normally closed contacts to CKT 1850 (BLK) to G200.

https://www.fixya.com/cars/t8706315-2003_gmc_yukon_xl_denali_low_beam

Bright lights wont shut off ? Assume you mean high beams ? Reading how they work might thing high beam relay has stuck contacts inside .

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.

Did you test the low beam electrical circuit using a volt meter ? Look at a wiring diagram to see what all is involved in turning the lights on ? Do you know how to test electrical circuits ?
Also reading service repair manual about the head lamps opp. would be a good thing to do .
Headlamps
The major common components of this system are the body control module (BCM), ambient light sensor, multifunction switch, park brake switch, and the headlamps.
The headlamps may be turned on in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, normal operation occurs. Second, with the headlamp switch is placed in the AUTO position, automatic lamp control (ALC) occurs. During ALC control, the headlamps will be in daytime running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions.
The low beam relay and high beam relay receive battery positive voltage directly from the battery through the HDM and COILS fuses in the underhood fuse block. The BCM supplies a ground signal to the low beam relay coil for automatic headlamp control and normal headlamp operation. The BCM also supplies ground to the high beam relay coil for high beam headlamp operation. When the driver places the headlamp switch in the HEADLAMP position and the dimmer switch is in the low beam position, the low beam relay energizes sending current flow through the left and right low beam headlamp fuses to both low beam headlamps. The dimmer switch sends a ground signal to the BCM in the high beam position and a momentary ground signal in the flash-to-Pass (FTP) position from G102 to deactivate the low beam headlights and activate the high beam headlights. With the headlights in the low beam position, the high beams may be momentarily turned on or flashed by activating the FTP portion of the switch.

Low Beams - Standard
The standard low beam headlamps receive voltage from the headlamp driver module located in the underhood fuse block. The body control module (BCM) controls the headlamp driver module with the headlamp low beam relay control circuit. Low beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamps are requested ON and the headlamp dimmer switch signal circuit is open, the BCM sends a pulse width modulated (PWM) ground signal though the headlamp low beam relay control circuit to the headlamp driver module which illuminates the low beam headlamps at a 100 percent intensity level. The right and left low beam circuits are independent and are fused separately in the underhood fuse block. The LOW HDLP-RT 10A fuse supplies voltage to the right low beam headlamp and the LOW HDLP-LT 10A fuse supplies voltage to the left low beam headlamp. The right and left headlamps are grounded at G103 and G107 respectively.

Your best bet mite be to have a qualified technician check it

What code's ? # code's P0 what ? Any BCM - body control module code's ? Did you do diagnostic test's for said code's ? Do you know what a factroy diagnostic flow chart is ? Is the vehicle a 4X4 or 2X4 ? What engine ? Do you know what class 2 serial data bus is ? Do you have wiring diagrams ?
Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch headlamp on signal circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.

High Beams
The high beam headlamps receive voltage from the headlamp HI relay located in the underhood fuse block. The body control module (BCM) controls the relay on the headlamp high beam relay control circuit. High beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is grounded, the BCM grounds the headlamp high beam relay control circuit, illuminating the high beam headlamps. The right and left high beam circuits are independent and are fused independently in the underhood fuse block. The right and left headlamps are grounded at G100 and G104.
The high beam indicator is illuminated when the instrument cluster receives a class 2 serial data message from the BCM that the high beams are illuminated.
Low Beams
The low beam headlamps receive voltage from the headlamp LOW relay located in the underhood fuse block. The body control module (BCM) controls the relay on the headlamp low beam relay control circuit. Low beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is open, the BCM grounds the headlamp low beam relay control circuit, illuminating the low beam headlamps. The right and left low beam circuits are independent and are fused independently in the underhood fuse block. The right and left headlamps are grounded at G100 and G104.

DTC B2645
The body control module (BCM) monitors the ambient light sensor signal circuit in order to determine if the daytime running lights (DRL) or the auto headlights (ALC) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor signal voltage is between 1.75-4.9 volts, either the DRL will be commanded ON or the ALC will be commanded ON depending upon the amount of light received by the sensor.

DTC B2645 Ambient Light Sensor Circuit

The relay isn't being energized (turned on ) That's why there is no power to the fuse's . Probably the switch is bad , but without testing that would be a guess . Have someone switch the headlamps from high to low , do you feel the relay click on ? Does the car have auto light's ? do they work ? Do you know what a wiring diagram is ? How to read one ? Use a volt meter to test electric circuits ? Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info. year , make , model an engine . Under system click on lighting , then under subsystem click headlamp's . You should see battery voltage at two of the relay pin's , If you look on the bottom of the relay you should see four set's of numbers 30 ,87 & 85 , 86 . If you jumped pin 30 & 87 together with a piece of wire the light's should work . Jump where the relay plugs into the fuse / relay box , not the pin's on the relay . The switch isn't giving ground anymore , this would energize the relay turning on the low beams . Check out the wiring diagram , hope these makes sense .

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

Has to be a bad turn signal , hi low beam switch ( multifuction switch) . The BCM - body control module turns the headlamps on with input from the switch .

Confirm that the light on alarm does not chime when the key is removed and the driver door is opened. If the alarm sounds than it is likely a body control module problem or circuit problem telling the lights to stay on.
If the alarm does not chime then I would check for a faulty relay. There are removable relays in the lighting circuits. Pull the relay and confirm that the lights remain off. The relay can have the internal contacts stuck together. Usually there are more than one relay of the same type in the under hood relay box. Replace the light circuit relay with an another identical part from another circuit and see if it corrects the problem. If so replace the relay. They are available from all auto parts store.

If the bulbs are good, it could be the dimmer switch portion of the multi-function switch, or the body computer. There is a 15amp fuse that powers the low beam relay in the fuse and relay box in the engine compartment. The body computer gets a signal from the dimmer switch and activates the low or high beam relay.
You may need a book with wiring diagrams to test the circuits.