Why are my turn signals, low beam lights and daytime running lights not working?

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 .

Hello. It seems your Chevrolet has either faulty headlamp relay(s) or its headlamps are connected in series; if one don't light, neither will the other one. I can't explain why the 'CHECK ENGINE' light was still on while your truck's engine was off and key was out of ignition switch. Good luck and keep me informed; if you want to.

That piece you think is a ceramic DRL module is a resistor , When in DRL mode voltage to the low beam headlamps circuit goes through that resistor dimming the headlamps from low beam to daytime running lamps . It sounds to me like you need a new resistor ,but without doing some electrical testing it could be a lot of things . The DRL relay in the under hood fuse box could have a problem , could be the BCM - body control module , the ambient light sensor etc... Here is how daytime running lamps work .
Daytime Running Lamps (DRL)
The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the daytime running lights (DRL) or the headlights. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. With the headlight switch in the OFF position, the headlights will either be turned ON or OFF, after an approximate 30 second delay depending on whether daylight or low light conditions are sensed. The HTR A/C IGN fuse in the underhood junction block supplies ignition positive voltage to the daytime running lamp (DRL) relay coil circuit. The DRL relay switch contacts are connected to the low beam circuit. When the headlamp switch is placed in the OFF position, the BCM will either turn on or off the daytime running lamps, depending on whether daylight or low light conditions are sensed. The BCM energizes the DRL relay, closing the switch contacts and grounding the low beam circuit. Ground is provided at G101. The DRL illuminate the low beam headlights at a reduced intensity. The DRL will operate when the ignition switch is in the ON position, the gear selector is not in the PARK position and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

No on the fuse . The LH HDLP and RH HDLP fuse in the fuse block - under hood, supply battery positive voltage to both low and high beam lamps at all times. For manual operation, when the headlamp switch is in the ON position, the headlamp switch supplies ground directly to the headlamps and to the body control module (BCM) on the headlamp low or high beam signal circuit, depending on the position of the headlamp dimmer switch. The BCM uses this signal to determine if the conditions are present to illuminate the daytime running lamps or park lamps.
The headlamps may be turned on 2 different ways. First, when the driver places the headlamp switch in the ON position, for manual operation. Second, with the headlamp switch placed in the OFF position activating automatic lamp control (ALC).For ALC operation, the BCM receives a signal from the ambient light sensor indicating a low or high ambient, outside, light level. Under low light conditions the BCM grounds the headlamp relay control circuit energizing the headlamp control relay. The now closed relay supplies ground through the headlamp switch to the headlamps and the BCM on the headlamp low or high beam signal circuit, depending on the position of the headlamp dimmer switch. When the BCM grounds the headlamp relay control circuit it also grounds the park lamp relay control circuit illuminating the park lamps. The headlamp relay is grounded at G203.
Daytime Running Lamps (DRL)
The low beam headlamps operate at reduced intensity when in daytime running lamps (DRL) mode. The ground circuit to the switch side of the DRL relay has a resistor in-line to reduce the intensity of the low beam headlamps for DRL operation. The body control module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient, outside, light level. Under daylight conditions the BCM grounds the DRL relay control circuit energizing the DRL control relay. The now closed relay supplies ground directly to the low beam headlamps and to the BCM on the headlamp low beam signal circuit. The low beam headlamps now illuminate with reduced intensity. The DRL relay is grounded at G203. Any time the headlamps are illuminated the DRL will not illuminate. Manual park lamps do not effect DRL operation.

It's the dimmer switch. Which is called the multifunction switch or turn signal switch. Just because it clicks, doesn't mean the it is working properly. If you click and the high beams come on, then click it again and have no low beams, replace the switch. Daytime running lights are controlled by the Body control module.

Daytime running Light module is overheating / it reduces power to low beam to create daytime running light . Ask yourself do I need this - If no law against it = UNPLUG control module . Your low beams will operate normal by turning on switch - Lever / Turn switch will turn on Highbeams but this switch can be Lose internally and Only cure is replace Signal Light Steering wheel switch . Common issue for all Cars is switch stalk / Lever is worn out by Aggressive use. If your car has Automatic light control - re they turn off after 30 second delay when you exit car - Try putting switch in manual mode means you Turn on - off by switch . But I really feel signal stalk is worn . DRCM is a known issue that can be unplugged . Final cheap solution unplug both high beams an Drive on low beam . $$$$$$$ spent chasing small problem will destroy $$$ needed for Bigger issues .

The diagram is left rear turn. For the turn signal, the top wire is voltage and the bottom black wire is ground. If the other lamps in that assembly work, the ground should be ok.
At the moment, I suspect you flasher or a wiring circuit problem. For rear turn signals, red wire with white tracer and red wire with blue tracer are the voltage wires for right and left turn at the rear. If you missing voltage, I'd have to use test light and start testing.

This is usually caused by a failed front control module as this unit controls the lighting on the vehicle!
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test your low beam wiring with a multimeter, if you have voltage install a new bulb.

There could be a fuse for each low beam light either under the hood or under the dash. If not, then prob both low beams are bad.

If you have daytime run lights, the following may be of help.

There is a daytime running light module that controls both low beams and the daytime running lights. The low beam bulbs may be OK. The high beams will work fine as they are not controlled through the module.

It may be possible to disable the daytime run lights by cutting the yellow wire going into the module and then connecting it to ground. Tape off the other end.

This will help. Thanks please keep updated.please do rate the solution positively .thank you for using fixya