2004 avalanche tailgate lock will not unlock and the tailgate is up without access to the inside. The lock turns to the unlock position but does not unlock.

LOCKING AND UNLOCKING
You can use the power door lock control or the remote control to lock and unlock your doors and tailgate.See Tailgate Lock.
Power Door Locks
The power door lock control is on the driver and front passenger door panels.

AUnlock.
BLock. Remote Control
You can use the remote control at any time your vehicle is not running.
Unlocking the Vehicle (Two-Stage Unlock)
Press the button to unlock the driver door. Press the button again within three seconds to unlock all doors.The direction indicators flash. The direction indicators flash twice to confirm the change. The unlocking mode applies to the remote control, keyless entry keypad and intelligent access.
Press and hold both the lock and unlock buttons on the remote control for four seconds to disable or enable two-stage unlocking. Disabling two-stage unlocking allows your entire vehicle to unlock with one press of the button.
Intelligent access at the driver door unlocks your entire vehicle when you disable two-stage unlocking.
Locking the Vehicle
Press the button to lock all doors.The direction indicators flash.
Press the button again within three seconds to confirm that all the doors are closed.The doors lock again, the horn sounds and the direction indicators flash if all the doors are closed.
Mislock
If any door is open, or if the hood is open on vehicles with an anti-theft alarm or remote start, the horn sounds twice and the direction indicators do not flash.
Activating Intelligent Access
General Information
You can unlock and lock the vehicle without taking the keys out of your pocket or purse when your intelligent access key is within 3 ft (1 m) of your vehicle. Intelligent access uses a sensor on the back of the door handle for unlocking and a separate sensor on the face of each door handle for locking.
The system does not function if:

• Your vehicle battery has no charge.
• The key battery has no charge.
• The key frequencies are jammed.

Note: The system may not function if the key is close to metal objects or electronic devices, for example keys or a cell phone.
Note: If the system does not function, use the key blade to lock and unlock your vehicle. See Remote Control.
Unlocking Using Intelligent Access
With your intelligent access key within 3 ft (1 m) of your vehicle, touch the unlock sensor on the back of the door handle for a brief period and then pull on the door handle to unlock, being careful to not touch the lock sensor at the same time or pulling the door handle too quickly. The intelligent access system requires a brief delay to authenticate your intelligent access key fob.
Locking Using Intelligent Access
With your intelligent access key within 3 ft (1 m) of your vehicle, touch the outer door handle lock sensor for approximately one second to lock, being careful to not touch the unlock sensor on the back of the door handle at the same time. After locking, you can immediately pull on the door handle to confirm locking occurred without inadvertently unlocking.
Note: Do not use the outside door handle as a roof cargo strap.
At the Electronic Tailgate (If Equipped)
Press the exterior tailgate release button inside of the tailgate handle. The tailgate unlocks and opens. See Electronic Tailgate.
Smart Unlock
This feature helps to prevent you from locking your intelligent access key inside your vehicle's passenger compartment or rear cargo area.
If you leave your key in the ignition, when you open the driver door and lock your vehicle with the power door lock control, the doors lock then unlock.
You can still lock your vehicle with the key in the ignition by:

• Using the manual lock on the inside of the door.
• Locking the driver door with a key.
• Using the keyless entry keypad.
• Using the lock button on the remote control.

Smart Unlocks for Intelligent Access Keys
This feature helps to prevent you from locking your intelligent access key inside your vehicle's passenger compartment or rear cargo area.
When you lock your vehicle using the power door lock control (with the door open, vehicle in park and ignition off), your vehicle searches for an intelligent access key in the passenger compartment after you close the door. If your vehicle finds a key, all of the doors immediately unlock.
In order to override the smart unlock feature and intentionally lock the intelligent access key inside your vehicle, you can lock your vehicle after all doors are closed by using the keyless entry keypad, pressing the lock button on another intelligent access key or touching the locking area on the handle with another intelligent access key in your hand.
When you open one of the front doors and lock your vehicle using the power door lock control, all doors lock then unlock if the ignition is on.
Autolock
Autolock locks all the doors when:

• All doors are closed.
• The ignition is on.
• You shift into any gear putting your vehicle in motion.
• Your vehicle reaches a speed greater than 12 mph (20 km/h).

Autolock repeats when:

• You open then close any door while the ignition is on and your vehicle speed is 9 mph (15 km/h) or lower.
• Your vehicle reaches a speed greater than 12 mph (20 km/h).

Autounlock
Autounlock unlocks all the doors when:

• The ignition is on, all the doors are closed, and your vehicle has been moving at a speed greater than 12 mph (20 km/h).
• Your vehicle comes to a stop and you switch the ignition off or to the accessory position.
• You open the driver door within 10 minutes of switching the ignition off or to accessory.

Note: The doors do not autounlock if you electronically lock your vehicle after you switch the ignition off and before you open the driver door.
Enabling or Disabling Autounlock
You can enable or disable the autounlock feature in the information display or an authorized dealer can do it for you. See General Information.
Illuminated Entry
The interior lamps and select exterior lamps illuminate when you unlock the doors with the remote entry system.
The illuminated entry system turns off the lights if:

• The ignition is on.
• You press the remote control lock button.
• After 25 seconds of illumination.

The dome lamp does not turn on if the control is set to the off position.
The lights do not turn off if:

• You switch them on with the dimmer control.
• Any door is open.

Battery Saver
The battery saver turns off the interior lamps 30 minutes after you switch off the ignition if a door is open and the dome lamp switch is on. It turns off the interior lamps after 10 minutes if the dome lamp switch is off.
Accessory Mode Battery Saver for Intelligent Access Keys (If Equipped)
If you leave the ignition on after leaving your vehicle, it turns off 15 minutes after you close all of the doors.

If you have a Subaru alarm system, you need to press unlock twice in quick succession to unlock the tailgate (and the passenger doors).

There is also a 30mm round access panel on the tailgate inside trim panel. You can stick your finger in an unlock the tailgate. Your tailgate outside lock handle may be rusted solid, which is jamming the lock.

Had a similar problem, found the tailgate was not closed all the way. Close the tailgate real hard and then lock with the key fob.

some cars are fitted with a valet key/lock 3 keys supplied new 2 normal 1 with a flute running down the middle.key with flute will not unlock the tailgate/glove box.tailgate has 2 positions key upright=locks with central locking.key turned to the left,(or right,cant remember which)then released to upright,locked,needs key to access.independant of central locking.

the barrel is faulty and needs replaced

First thing: Try using the key to move to the locked and then to the unlocked position. If this works, open the tailgate... This also pretty much tells you what the root cause problem is, which is a pressed-in plastic post working its way out (see below).

If no bedliner, just remove metal plate inside tailgate and actuate by hand inside to open. If bedliner, first use a small screwdriver to carefully (don't scratch paint) push in latches at either side of tailgate to open/lower tailgate (if locking/unlocking as above did not work to lower gate and gain access). Next, use two blade screwdrivers to pry out the "buttons" that hold the ends of the tailgate liner where they wrap around the sides, then remove bedliner piece and metal plate, etc.

Once you have access to inside of tailgate, you will see how the mechanism works by pulling up and down on the handle while observing. You will probably find that the slide mechism that locks and unlocks the mechanism has been allowed to move such that it cannot unlock/allow movement of the latching mechanism. This is usually the result of the pressed in plastic anchor being worn/loose. I had some success with cleaning thoroughly with alcohol or brake cleaner, allowing to dry and then using super glue to hold it firmly in all the way. Still have to hold handle up when closing gate and keep key on hand to unlock every time opening, but it was a free repair...

Access the lock from the inside and try unlocking it with a screwdriver.

sounds like the tumbler is bad, try to replace it yourself , if you have an electronic chip in your key you have to go to dealer to get it installed. cheapest way to fix this is order a new locking tailgate handle from jc whitney or somewere and replace the whole thing.

I have the solution to every one out there with tailgate lock problems......I had the very same problem but wasnt interested in getting a power lock.......Here goes.....it costs you some wd40 or liquid wrench.....nothing else......open the tail gate.....you will see the screws that hold the handle in place.....take off the two outer screws only....then pop off the handle cover....yes it does come off without breaking.....you will see something shaped like a "C".....it should move back and forth.....with the tailgate closed you should be able to move that "C" back and forth...it swivels on a pivot you can see in the opening above the tailgate handle.......this is the lock mechanism.....mine was seized up.....anyways......with the tailgate still closed squirt some wd40 or liquid wrench in the area directly above the tailgate handle........that "C" thing will move again and your problem is over...email me if you figured it out........
I was delighted with the fix.....and it's so easy to do.....then put everything back in its place......tell everyone you know....