Can you tell me why my liftgate will not lock using my keyless remote entry.all the other doors lock my vehicle is a 2005 srx cadillac

The Lock's lock from the door switches ? If they do it's not a fuse problem . Which of these does your vehicle have ?
Keyless Entry System Description and Operation (with Accessory 2 Way Remote)
Keyless Entry System Description and Operation (without Accessory 2 Way remote)

The keyless entry system is a vehicle entry device. The keyless entry system is used in conjunction with the body control module (BCM) to remotely activate certain vehicle features. Keyless entry will lock/unlock the doors/liftgate when a corresponding button on the keyless entry transmitter is pressed. This is accomplished by the transmitter sending a radio frequency to the remote control door lock receiver (RCDLR). The RCDLR interprets the signal and activates the requested function via a serial data message to the BCM. A low transmitter or vehicle battery or radio frequency (RF) interference from aftermarket devices, such as 2-way radios, power inverters, computers, etc., may cause a system malfunction. High RF traffic areas may also cause interference that could lead to a malfunction. Keyless entry allows you to operate the following components:
• Door locks
• Liftgate lock
• Vehicle locator/Panic alarm
• Illuminated entry lamps
• Remote vehicle start
The keyless entry system has the following components:
• Keyless entry transmitters
• Keyless entry antenna
• 2 Way Advanced Remote Start RCDLR
• BCM

Your best bet , take it to a GM dealer .

Most GM vehicles of that vintage require a GM Tech II scanner to program the keyless entry. It is an expensive tool so a trip to the dealer is generally required. Some locksmiths may be able to program them as well.

Remote control door lock receiver (RCDLR)

The remote control door lock receiver (RCDLR) is a multifunction module that operates both the keyless entry system as well as the TPM system. When an RF message is received from a keyless entry transmitter, the RCDLR interprets this signal and will request via serial data that the body control module (BCM) perform the specific function, i.e. door lock, door unlock, or vehicle locate.

Remote Control Door Lock Receiver (RCDLR)
In the right rear quarter panel behind the interior trim panel

Theft Deterrent Arm/Disarm Modes
Important: Although mode 2 provides increased security, the content theft deterrent system disarms only by pressing unlock on the keyless entry transmitter. This can pose a problem if the keyless entry transmitter is damaged, lost, or inoperative for any reason while you attempt to disarm the content theft deterrent system.
Mode 1: The system arms when you lock the doors with the keyless entry transmitter. The system disarms when you unlock the left front, right front, or liftgate door with the key or the keyless entry transmitter. The system does not arm when you lock the doors with a power door lock switch.

Mode 2: The system arms when you lock the doors with the keyless entry transmitter. The system disarms when you unlock the doors with the keyless entry transmitter. The system does not disarm when you unlock the doors with the key.

Mode 3: The system arms when you lock the doors using a power door lock switch or the keyless entry transmitter. The system disarms when you unlock the left front, right front, or liftgate door with the key or the keyless entry transmitter.
Changing the Feature Customization Modes

1. Turn off the IP dimmer switch.
2. Turn the ignition switch to the LOCK position.
3. Remove the BCM PRGRM fuse.
4. Turn the ignition switch to the ACC position. The BCM flashes the fasten belts indicator and sounds the chime 4 times, which indicates that BCM type 4 is installed on the vehicle. At this point, the BCM has entered the feature customization mode.
5. In order to change the theft deterrent/shock sensor mode, turn the headlamp switch from OFF to PARK and back to OFF.
The BCM flashes the fasten belts indicator and sounds the chime a number of times equivalent to the theft deterrent/shock sensor mode. A transition past mode 4 repeats the sequence starting with mode 1.

6. Complete the following steps in order to change the theft deterrent arm/disarm mode:

6.1.
Insert the key in the left front, right front, or liftgate door lock cylinder.

6.2.
Rotate the key from the center to the unlock position.

6.3.
Press the horn button on the remote keyless entry transmitter.

6.4.
Count the number of chimes that you hear. The number of chimes tells you which mode you have set.

6.5.
Press the horn button again in order to change the mode. Continue to press the button until you hear the number of chimes that indicates the mode that you want.

6.6.
Turn the key back to the center position and remove the key from the door key cylinder.

In order to exit and save the current feature customization modes use the following procedure:

1. Turn the ignition switch to the LOCK position.
2. Reinstall the BCM PRGRM fuse.

If you are unable to change locking modes Theft Deterrent System Feature Customization Inoperative

There is a known TSB for this....
#07-08-52-003: Rear Liftgate Glass May Not Lock When Using Remote Keyless Entry (RKE)/Key Fob Transmitter/Door Lock Switch, Lifgtate Hatch or Liftgate Glass May Lock/Unlock When Rear Liftgate Glass Button Depressed - (Sep 13, 2007)


Subject: Rear Liftgate Glass May Not Lock When Using Remote Keyless Entry (RKE), Key Fob Transmitter or Door Lock Switch, And/Or Liftgate Hatch Or Liftgate Glass May Lock Then Unlock When Rear Liftgate Glass Button is Depressed (Reposition Lock Cylinder Wave Washer and Adjust Lock Rod)


Models: 2005-2007 Buick Rainier

2005-2008 Chevrolet TrailBlazer, TrailBlazer EXT, TrailBlazer SS

2005-2008 GMC Envoy, Envoy XL, Envoy Denali

2005-2008 Saab 9-7X




--------------------------------------------------------------------------------
Do This
Don't Do This

Reposition liftgate lock cylinder wave washer and adjust lock rod.
DO NOT replace the liftgate latch or actuator.


Condition
Some customers may comment on one or more of the following conditions:

• The rear liftgate glass may not lock when using the remote keyless entry (RKE), key fob transmitter or door lock switch unless the lock is pressed a second time.

• The rear liftgate or glass locks, but may be unlocked when the rear liftgate lock cylinder button is depressed.

• The rear liftgate locks but the liftgate glass may not lock.

Cause
These conditions may be caused by one or all of the following:

• The rear liftgate cylinder lock rod may be out of adjustment.





• The wave washer on the liftgate lock cylinder may be out of position with the cup side down.

• Excessive movement or slack in the lock rods at the liftgate bell crank assembly.





• The liftgate lock cylinder pawl may contact the rear liftgate glass latch when the lock cylinder button is depressed.

Correction
Important: Do Not remove the rear liftgate lock cylinder from the vehicle to perform this repair.

Reposition the rear liftgate lock cylinder wave washer and adjust the lock rod using the steps below.

Verify the customer's condition.

Open the liftgate.

Remove the upper liftgate garnish molding.

Remove the rear liftgate trim panel.

Remove the cylinder lock rod from the threaded lock rod retaining clip.

Tip
Place the tip of a screwdriver blade into the opening of the C-clip and slowly rotate the screwdriver to pry out the C-clip from the shaft. Then use needle-nose pliers to remove the C-clip.

Remove the C-clip from the rear liftgate lock cylinder push button and remove the wave washer.

Install the wave washer with the cup side up.

Position the wave washer with the curved edges of the wave spring parallel to the tabs on the lock cylinder shaft.

Important: Use needle-nose pliers to slightly squeeze the C-clip back into shape. Make sure the clip seated, you should feel a snap and hear an audible click.

Install the C-clip onto the shaft and in the slot using needle nose pliers. Then rotate the pawl several times to make sure the C-clip does not rotate. If the clip rotates then the clip is not fully seated.

Position the lock cylinder pawl to the full clockwise position.

Pull up on the cylinder lock rod to remove any slack in the bell crank.

Install the cylinder lock rod into the threaded lock rod retaining clip while removing any slack from the lock rod linkage.

Close the lock rod retainer clip.

Close the liftgate assembly.

Open the liftgate glass while keeping the liftgate closed.

Use the key fob to cycle the liftgate to the lock and unlock position while inspecting the rear liftgate pawl. The lock cylinder pawl should have clearance between the latch as shown above. If the pawl is contacting the latch, readjust the cylinder lock rod.

Verify that the customer's condition has been corrected.

Install the rear liftgate trim panel.

Install the upper liftgate garnish molding.

Is this an issue with all 2008 HHR remotes??? Highly doubtful , probably the vehicles keyless entry system . Taking the vehicle to a qualified repair shop an having the keyless entry system checked for DTC'S - diagnostic trouble code's . Do you know what a DTC is ?
The keyless entry system is a vehicle entry device. The keyless entry system is used in conjunction with the body control module (BCM) to remotely activate certain vehicle features. Keyless entry will lock/unlock the doors, or release the rear compartment lid when a corresponding button on the keyless entry transmitter is pressed. This is accomplished by the transmitter sending a radio frequency to the remote control door lock receiver (RCDLR). The RCDLR interprets the signal and activates the requested function via a serial data message to the BCM. A low transmitter or vehicle battery or radio frequency (RF) interference from aftermarket devices, such as 2-way radios, power inverters, computers, etc., may cause a system malfunction. High RF traffic areas may also cause interference that could lead to a malfunction. Keyless entry allows you to operate the following components:
• Door locks
• Liftgate lock
• Remote rear doors (Panel only)
• Vehicle locator/panic alarm
• Illuminated entry lamps
• Remote vehicle start
The keyless entry system has the following components:
• Keyless entry transmitters
• Keyless entry antenna
• 2 Way Advanced Remote Start RCDLR
• BCM

Guessing will not fix this .

#07-08-52-003: Rear Liftgate Glass May Not Lock When Using Remote Keyless Entry (RKE)/Key Fob Transmitter/Door Lock Switch, Lifgtate Hatch or Liftgate Glass May Lock/Unlock When Rear Liftgate Glass Button Depressed - (Sep 13, 2007)


Subject: Rear Liftgate Glass May Not Lock When Using Remote Keyless Entry (RKE), Key Fob Transmitter or Door Lock Switch, And/Or Liftgate Hatch Or Liftgate Glass May Lock Then Unlock When Rear Liftgate Glass Button is Depressed (Reposition Lock Cylinder Wave Washer and Adjust Lock Rod)


Models: 2005-2007 Buick Rainier

2005-2008 Chevrolet TrailBlazer, TrailBlazer EXT, TrailBlazer SS

2005-2008 GMC Envoy, Envoy XL, Envoy Denali

2005-2008 Saab 9-7X




--------------------------------------------------------------------------------
Do This
Don't Do This

Reposition liftgate lock cylinder wave washer and adjust lock rod.
DO NOT replace the liftgate latch or actuator.


Condition
Some customers may comment on one or more of the following conditions:

• The rear liftgate glass may not lock when using the remote keyless entry (RKE), key fob transmitter or door lock switch unless the lock is pressed a second time.

• The rear liftgate or glass locks, but may be unlocked when the rear liftgate lock cylinder button is depressed.

• The rear liftgate locks but the liftgate glass may not lock.

Cause
These conditions may be caused by one or all of the following:

• The rear liftgate cylinder lock rod may be out of adjustment.





• The wave washer on the liftgate lock cylinder may be out of position with the cup side down.

• Excessive movement or slack in the lock rods at the liftgate bell crank assembly.





• The liftgate lock cylinder pawl may contact the rear liftgate glass latch when the lock cylinder button is depressed.

Correction
Important: Do Not remove the rear liftgate lock cylinder from the vehicle to perform this repair.

Reposition the rear liftgate lock cylinder wave washer and adjust the lock rod using the steps below.

Verify the customer's condition.

Open the liftgate.

Remove the upper liftgate garnish molding.

Remove the rear liftgate trim panel.

Remove the cylinder lock rod from the threaded lock rod retaining clip.

Tip
Place the tip of a screwdriver blade into the opening of the C-clip and slowly rotate the screwdriver to pry out the C-clip from the shaft. Then use needle-nose pliers to remove the C-clip.

Remove the C-clip from the rear liftgate lock cylinder push button and remove the wave washer.

Install the wave washer with the cup side up.

Position the wave washer with the curved edges of the wave spring parallel to the tabs on the lock cylinder shaft.

Important: Use needle-nose pliers to slightly squeeze the C-clip back into shape. Make sure the clip seated, you should feel a snap and hear an audible click.

Install the C-clip onto the shaft and in the slot using needle nose pliers. Then rotate the pawl several times to make sure the C-clip does not rotate. If the clip rotates then the clip is not fully seated.

Position the lock cylinder pawl to the full clockwise position.

Pull up on the cylinder lock rod to remove any slack in the bell crank.

Install the cylinder lock rod into the threaded lock rod retaining clip while removing any slack from the lock rod linkage.

Close the lock rod retainer clip.

Close the liftgate assembly.

Open the liftgate glass while keeping the liftgate closed.

Use the key fob to cycle the liftgate to the lock and unlock position while inspecting the rear liftgate pawl. The lock cylinder pawl should have clearance between the latch as shown above. If the pawl is contacting the latch, readjust the cylinder lock rod.

Verify that the customer's condition has been corrected.

Install the rear liftgate trim panel.

Install the upper liftgate garnish molding.

To unlock the liftgate, press the unlock button on the Remote Keyless Entry (RKE) transmitter twice or use the power door lock switch.
To lock the liftgate, press the lock button on the RKE transmitter or use the power door lock switch. The liftgate does not have a key lock cylinder.
To open the liftgate, pull up on the handle located in the center of the liftgate.
When closing the liftgate, use the molded handles to pull the liftgate down. Push the liftgate closed until it latches.

Check with the dealer to see if you can get another remote keyless entry with a tailgate button more recessed back. It sounds like the button is too high on the pad and it needs to be recessed into the pad a bit more. Just trying to keep you safe.

if it was mine I would take the rear inside door panel off and see if there is any rust or bind in the power door lock motor itself and also make sure that no one has broken a key off or stuck anything in the lock cause I had an expedition with this same problem and it was a broken key in the lock