My door lock is not working on my cts 2008 rear door.

Question edited for clarity and add maker.
Question moved to model Category.

Covered by two relays

Cadillac CTS (2008-2014) fuses and relays

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Here you will find fuse box diagrams of Cadillac CTS 2008, 2009, 2010, 2011, 2012, 2013 and 2014, get information about the location of the fuse panels inside ...
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Cadillac CTS (2008) - fuse box diagram - Auto Genius

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Sep 25, 2016 - The rear compartment fuse block is located on top of the battery, on the right side of the trunk. The battery access door must be removed to ...

2008 Cadillac CTS fuse box diagram - StartMyCar

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The 2008 Cadillac CTS has 2 different fuse boxes: Underhood Fuse Block diagram. Rear Compartment Fuse Block diagram. * Cadillac CTS fuse box diagrams change ...

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Cadillac CTS (2008-2014) fuses and relays

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2010, 2011, 2012, 2013, 2014 - Here you will find fuse box diagrams of Cadillac CTS 2008, 2009, 2010, 2011, 2012, 2013 and 2014, get information about the ...

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  Fuse Box Diagram Cadillac

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  Fuse box diagrams (location and assignment of the electrical fuses and relays) ... of electrical fuses and relays) for Cadillac CTS (2008, 2009, 2010, 2011, ...

Cadillac CTS (2011 - 2014) - fuse box diagram - Auto Genius

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Sept 28, 2016 - Rear Compartment Fuse Block (CTS Coupe and Sedan) ... The rear compartment fuse block is located on top of the battery, on the right side of the ...

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Do you know anything about automotive electronic's ? The trunk release is controlled by electronic control modules . Having the vehicle check for DTC'S - diagnostic trouble code's should be the first step in the diagnostic procedure . Then reading how it work's !
Factory service repair info.
Rear Compartment Lid Release System Components
• Body control module (BCM)
• Remote control door lock receiver
• Interior rear compartment lid release switch
• Exterior rear compartment lid release switch
• Rear compartment lid release actuator
• Trunk release relay

Rear Compartment Lid Release Operation
The interior rear compartment lid release switch receives a signal from the driver door switch assembly (DDSA). When the interior rear compartment lid release switch is activated, the signal circuit is pulled to ground. The DDSA interprets this and sends a GMLAN serial data message to the body control module (BCM) requesting the rear compartment lid be released. The BCM responds by applying battery voltage to the trunk release relay control circuit which energizes the TRUNK RELES relay. The trunk release relay is supplied with battery voltage at all times. With the relay coil energized, the relay switch contacts close allowing battery voltage to flow to the rear compartment lid release actuator causing the rear compartment lid to release. The rear compartment lid release actuator is permanently grounded at G402.

The trunk release relay is located in the rear fuse box located under the back seat.

to see if it is a switch problem see if the locks work from their respective doors, if the locks work from the switch's on the back doors and not from the drivers switch then the drivers switch is bad. If the locks don't work right from any of the switches then the door lock solenoids are bad. the solenoids are not too hard to change if you are mechanically inclined, switches are not too hard either

see the diagram attached. YOu must test the mechanism for lube, or damage parts, loose wires or connector corroded, switch dirty Lube WITH wd-40, test the motor or solenoid
God bless you

Testing would need to be done , scan tool hooked up checking DTC'S - diagnostic trouble codes . View data etc...
Keyless Entry System Description and Operation - Active
The keyless entry system is a vehicle entry device. The keyless entry system is used in conjunction with the door locks to unlock the vehicle. Keyless entry will lock/unlock a door or open 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. A low transmitter 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, such as gas stations that use pay-at-the-pump RF transponders, may also cause interference that could lead to a malfunction. Keyless entry allows you to operate the following features:
• Door lock/unlock
• Rear compartment lid release
• Illuminated entry lamps
• Panic alarm/Vehicle locator
• Remote vehicle start

Your best bet , take it to a qualified repair shop . Dealer

gm had and has a lot of door lock actuator failures replace the lock actuator it will be fine

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 .

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.

bang on the door hard and put the window up.if there is a dead spot in the motor from lack of use,the motor will start.