Where are the door lock relays in the 2008 Avalanche?

Dannie, power lock actuator faulty. Check the attached links,instruction and guides, Good luck
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Those new chevys have option for setting how the locks work,,, check it the settings menu on the dash,,,also the doors will not lock with engine off and key in the ignition,, even with the fob,,,also check the child safty switches to on rear doors,, and the relays under hood,,, just a few suggestions

problem ground wire on the BCM is logical after the cluster replacement

Do the power windows work ? DDM - driver door module fuse 15 amp - location is the instrument panel fuse box , plus LT DR circuit breaker 25 amp. Circuit breakers rarely go bad . The power locks are controlled by electronic's .The passenger side has another power supply ,that's why they still work .
Door Lock System Components
The power door lock system consists of the following components:
• The driver door switch (DDS)
• The passenger door switch (PDS)
• The body control module (BCM)
• The driver information center (DIC)
• The rear door lock/unlock relay (LBEC)
• The reversible door lock actuators in each of the doors and liftgate

The front power door lock switches are integral components of the driver door module (DDS) and passenger door module (PDS). The switches are 2 position normally open rocker switches. When placed in either the lock or unlock positions, the switches provide a direct input to the DDS or PDS. The DDS or PDS monitors these inputs and sends a LAN message indicating a change in the switch's respective position. Modules which activate the power door lock motors receive the LAN message and activate the motor in the appropriate direction to lock or unlock the vehicle's doors and liftgate. The rear door lock switch provides a lock and unlock signal to the body control module (BCM). The BCM upon receipt of a lock or unlock signal will control the rear door lock/unlock relay and also send a LAN message to the DDS and PDS to perform the appropriate function.
The modules which activate the power lock motors are:
• The DDS (driver door lock actuator)
• The PDS (passenger front door lock actuator)
• The BCM (both rear door lock actuators and cargo door/liftgate)
The DDS and PDS are directly connected to the respective door lock actuator through the door lock motor lock and unlock circuits. Once a door lock or unlock request has been received, the module will supply battery voltage to one side of the actuator and ground the other causing the doors to lock or unlock.
The rear passenger and endgate doors are controlled by the BCM through the rear door lock/unlock relay which is incorporated onto the printed circuit board in the LH BEC. The BCM controls the unlock relay by providing ground to energize the coil and controls the lock relay by providing battery voltage to energize the relay coil. The energized the relay and allows voltage to be applied to either the door lock motor lock or unlock circuits. Since the other side of the door lock actuator is connected to the normally closed contacts of the opposing relay to ground, the doors lock or unlock.

It's possible you have broken wire or wires inside the flex boot from the body of the vehicle to the driver's door . This happens a lot .
Fuse Block - I/P instrument panel
Left of the I/P behind the side trim panel

the door lock actuators have most likely gone bad.

Does the switch inside for that door work ? Does the power window work for that door ? Check fuse DDM - 15 amp I/P fuse panel . Do you know where the insturment panel fuse box is located ?
Fuse Block - I/P
Left of the I/P behind the side trim panel
# 4
DDM Fuse
15A
Driver Door Module (DDM)

Do you know anything about automotive electronic's , control module's ? Serial data communication networks ?
Circuit/System Description
The driver and passenger door lock and side window switches are integrated control module switch assemblies. The DDS and PDS door lock switches are normally open, 2 position rocker type switches, with detents for lock and unlock. The DDS and PDS are directly connected to the respective door lock actuator through the door lock actuator control circuits. When a door lock or unlock function is activated from the DDS or PDS, a serial data message lock or unlock command is sent to the other door switch and body control module.

It could be the power lock motor. You could have a short or bad wiring harness. Might just be a fuse that connects to both. But since you said it's only the driver side. When the power lock motor is bad it can trigger your alarm because they're wired together.

Hope that helps. Good luck.

each door has there own door lock solenoid, the only thing they have in common is one fuse, either they all work or none of them will work. So I would say the door lock actuator inside the door has failed.

You need to remove the carpet on the passengers side and check the wireing harness,take off the tape and visually inspect it.You are likely to find broken splices ,bare wires or wires shorted to each other or to ground.