I have a 2006 Yukon SLT and the problem is that the liftgate doesn't work any longer. All the doors still work with the keyless entry but not the back liftgate. Please help..

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 .

The vehicle horns are activated under the following conditions:
?€¢
The horn switch is depressed.

?€¢
The body control module (BCM) commands the horns on. The BCM commands the horns on under either of the following conditions:

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When the content theft deterrent system detects a vehicle intrusion. For further information, refer to Content Theft Deterrent (CTD) Description and Operation in Theft Deterrent.

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When the panic button is depressed on the remote control door lock transmitter. For further information, refer to Keyless Entry System Description and Operation in Keyless Entry.

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When the OnStar?® system is used to sound the horns, if equipped. For further information, refer to OnStar Description and Operation in Cellular Communications.

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When the keyless entry system is used to lock the vehicle, a horn chirp may sound to notify the driver that the vehicle has been locked. The notification feature may be enabled or disabled through personalization. For further information, refer to Keyless Entry System Description and Operation in Keyless Entry

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

yes

Hi Nick
this problem have nothing to do with the key fob.
your radio back_up power fuse is blown, look for it and replace it
good luck

remote sensor for what?

The keyless entry system has the following main components:
• The transmitters
• The passenger door module (PDM)
The PDM communicates with the body control module (BCM) through the keyless entry serial data circuit. When you press a button on a transmitter, the transmitter sends a signal to the PDM. The PDM sends a request to the BCM and the BCM performs the appropriate function.

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 .

my remote start ont work but door locks work 2007 buick

The keyless entry is designed to work with the doors closed (closed - not locked). If the door ajar sensor thinks the door is open the keyless entry is disabled. When you manually lock the door it might tighten the door just enough to activate the keyless entry. I would try slamming all the doors closed and then see if the keyless entry works. If it still wont work have the wiring checked on the front door lock.