Turn signal/dimmer switch,turn signal will not stop if switch is in high beam position. will not work (signal) if in low beam position. Audi 2004 (07/03 build date) s4 with 4.2 litre v8

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

Ive changed the relay and the headlight switch on the dash .. still wont turn off headlights ? Just changing parts won't fix it , need to test . Hooking up a professional scan tool , one that can read codes in the BCM - body control module is the way to start to find the problem . Then familiarize yourself with how they work.

Headlamps
Major components of this system are the body control module (BCM), headlamp relay, beam select relay, ambient light sensor, headlamp and panel dimmer switch, turn signal/multifunction switch, park brake switch, and the low and high beam headlamps.
The headlamps may be turned ON in 2 different ways. First, when the driver places the headlamp switch in the ON position, normal operation occurs. Second, when the headlamp switch is placed in the AUTO position, automatic lamp control (ALC) operation occurs. During ALC control, the headlamps will be OFF in daylight conditions or in low/high beam operation in low light conditions.
The headlamp relay receives battery positive voltage directly from the battery. The BCM supplies a ground signal to the headlamp relay for normal headlight operation. The BCM also supplies voltage to the beam select relay coil for high beam headlight operation. When the driver places the headlamp switch in the ON position and the dimmer switch is in the low beam position, the headlamp relay supplies current flow through the left and right low beam headlamp fuses to both low and high beam headlamps. Both low beam headlights are grounded through the beam select relay. When activated, 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 G106. The BCM then energizes the beam select relay which switches the headlamp grounds from the low beam headlight bulbs to the high beam headlight bulbs illuminating 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.
The instrument panel cluster (IPC) illuminates the high beam indicator when the BCM detects that the high beams are requested. The IPC receives a class 2 message from the BCM requesting illumination.
The Headlamps On at Exit and Perimeter Lighting modes can be adjusted using the steering wheel controls to select the function as displayed in the driver information center (DIC). The Headlamps On at Exit selection will allow the driver to customize the period of time that the headlamps remain illuminated upon exiting the vehicle. This period can be adjusted from 0-180 seconds. The Perimeter Lighting feature allows the driver to select if they want the headlamps and backup lamps to illuminate when the door UNLOCK button on the key fob is activated. This feature can be turned ON or OFF by using the DIC steering wheel control buttons.

DTC B2575 Headlamp Control Circuit

Circuit Description
When the body control module (BCM) senses a request for headlamp or daytime running lamp (DRL) illumination, the BCM sends a ground signal to the headlamp relay through the low beam headlamp relay control circuit. The headlamp relay will illuminate the low beam headlamps.

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, command the headlamps ON and OFF.
Does the headlamp relay turn ON and OFF with each command?

Do you know what bi-directional control means ? Need a professional scan tool to do these type of test .

DTC B2602: Daytime Running Lamp Control Circuit Low or Open
DTC B2603: Daytime Running Lamp Control Circuit High

Without this type of info. from service repair manual an using a scan tool your missing the big picture .

I would check the fuses first. Headlights are typically on a separate fuse then the parking lights. If the fuse is fine check and see if the Bulb is burnt out but it is rare for both lights to go out at the same time.

Likely a bad ground, but could be a fuse(s), or a failed multifunction switch, or BCM. It requires circuit testing to identify the cause.

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 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

Do you know anything about automotive electronics ? Electronic control modules .
Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input 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.
If the headlight switch is left in the ON position, the inadvertent power control feature will turn OFF the headlights approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until turned OFF or the battery runs dead.
The high beam indicator is illuminated when the instrument cluster receives a GMLAN serial data message from the BCM that the high beams are illuminated.
High Beams
The high beam headlamps receive voltage from the headlamp high relay located in the underhood fuse block. The 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.
Low Beams - Standard
The low beam headlamps receive voltage from the headlamp low beam relay located in the underhood fuse block. The 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 are fused independently in the underhood fuse block.

Hooking up a factory scan tool an checking DTC'S - diagnostic trouble codes would be the very first step in trouble shooting this problem .
DTC B257A 00: Headlamp Switch Input Signal Mismatch
DTC 2575 00: Headlamp Control Circuit

Not a fuse problem , same fuse power's low an high beams . Looking at wiring diagrams an using a DVOM - digital volt ohm meter to test the electrical circuit's is the way to find the problem . The light's staying on for 3 or 4 min's. is a function of the BCM - body control module ! Do you know anything about automotive electrical testing ? Do you know what a wiring diagram is an how to read one . Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. Year , make , model an engine size . Under system click on lighting ,then under subsystem click on headlamps .Click the search button then the blue link. get yourself a cheap DVOM an test the electrical circuit's , this is how electrical problems are solved .
Electric Testing Techniques You Need to Know
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts

Plus reading factory service repair info for how it should work would be a good idea .

Headlamps
The headlamps may be turned on two 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 OFF position, for automatic lamp control (ALC). During ALC, the headlamps will be in day time running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions. The LH HDLPand RH HDLP fuses, supply battery positive voltage from the underhood junction block to the left and right headlamps. The circuit continues through both low and high beam lamps, then back to the underhood junction block. The low beam and high beam circuits continue to the headlamp switch. The low beam and high beam circuits also provide the body control module (BCM) with both low and high beam inputs. The headlamp switch includes the dimmer switch and the flash-to-pass switch. When the headlamp switch is placed in the HEADLAMP position a path to ground is provided. Ground is provided at G201. Depending on the position of the high/low beam switch, either the low or high beam circuit will now have power and ground.
The LH HDLP fuse in the underhood junction block, supplies battery positive voltage to the automatic lamp control (ALC) headlamp relay coil circuit. The ALC relay switch circuit is connected to the low beam circuit at the headlamp switch. When the headlamp switch is placed in the OFF position, the BCM will automatically turn on the low beams in low light conditions. The BCM energizes the ALC relay, closing the switch contacts and grounding the low beam circuit. Ground is provided at G201. With the headlights in the low beam position, the high beams may be momentarily turned on or flashed with the dimmer switch handle. The flash-to-pass feature is accomplished by pulling the dimmer switch handle toward the driver. The headlights may be switched to high beam with the opposite movement of the dimmer switch lever. When the headlamp dimmer switch handle is pulled toward the driver, the flash-to-pass switch closes grounding the high beam circuit. Ground is provided at G201. Both high beams will remain on until the driver releases the switch handle.
If the driver places the headlight switch in the HEADLAMP position , the headlights will remain on until turned off or the battery runs dead.
Do you know what a factory diagnostic trouble shooting chart is ?

Headlamps Inoperative - Low Beams

Step
Action
Yes
No
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics
1
Did you perform the Lighting System Diagnostic System Check?
YES - Go to Step 2
NO - Go to Diagnostic System Check - Lighting Systems
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 in Wiring Systems
NO - Go to Step 3
3
Disconnect the turn/headlamp wiper switch assembly 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 wiper switch assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
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 in Wiring Systems.
YES - Did you complete the repair?
NO - Go to Step 7
--
6
Replace the turn/headlamp wiper switch assembly. Refer to Multifunction Turn Signal Lever Replacement - On Vehicle in Steering Wheel and Column.
Did you complete the replacement?
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 3

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