My key suddenly will not unlock my driver's door on my 2004 Rendezvous! I do not have a keyless entry system on this vehicle, and there is only one key entry on the entire vehicle on the driver's door. This has never happened before, and the key was working fine three days ago. The vehicle has not been driven since then.

Do they work with the key fob, do you have one of those? They lock when put into gear an unlock when put into park because the BCM - body control module does that .

Door Lock System Components
The power door lock system consists of the following components:
• Driver door lock switch
• Front Passenger door lock switch
• Body Control Module (BCM)
• Relays: Driver Door Unlock -- on vehicles with RFA, Door Unlock, and Door Lock
• Door Lock fuse 15A
Door Lock System Controls
The power door lock system can be controlled by any of the following:
• A power door lock switch activation
• A keyless entry command -- if equipped with keyless entry


Driver and Passenger Door Lock Operation
When any of the door lock switches is pressed to the lock position, the BCM door lock/unlock signal circuit changes from an idle voltage of ~3.4 volts to 0.0 volts generating a lock command. The BCM then applies battery positive voltage to the Door Lock Relay, which in turn applies battery positive voltage to the Door Lock Actuator lock circuit of all the Door Lock Actuators. Since the Door Lock Actuator unlock circuits are held to ground through the resting Door Unlock Relay(s), the actuators execute the lock command, locking the doors.
The lock function can also be accomplished by the BCM having received a keyless entry door lock command, if the vehicle is equipped with keyless entry.


Driver and Passenger Door Unlock Operation

When any of the door lock switches is pressed to the unlock position, the BCM door lock/unlock signal circuit changes from an idle voltage of ~3.4 volts to ~1.7 volts generating an unlock command. The BCM then applies battery positive voltage to the Door Unlock Relay and the Driver Door Unlock Relay when equipped with keyless entry, the relay(s) in turn apply battery positive voltage to the Door Lock Actuator unlock circuit of all the Door Lock Actuators. Since the Door Lock Actuator lock circuits are held to ground through the resting Door Lock Relay, the actuators execute the unlock command, unlocking the doors.
The unlock function can also be accomplished by the BCM having received a keyless entry door unlock command, if the vehicle is equipped with keyless entry. Keyless entry personalization allows the driver door to be unlocked individually before unlocking the passenger doors. When this feature is active, the BCM will require a repeated unlock command to unlock the passenger doors.


Automatic Door Lock/Unlock
The automatic door lock/unlock function is a Vehicle Personalization feature with the following four programmable modes of operation:
The automatic door lock feature is disabled.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and all of the doors Unlock when the vehicle is shifted into Park.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and only the driver door Unlocks when the vehicle is shifted into Park.
For information on programming the automatic door locks, refer to Vehicle Personalization in Personalization.

What alarm ? Horn an do the lights flash ?
The content theft deterrent (CTD) system, when armed, is designed to deter vehicle content theft by pulsing the horns and exterior lamps for approximately 30 seconds when an unauthorized vehicle entry is detected. However, the CTD System does not affect engine starting.
An unauthorized entry can be any of the following with the CTD System armed:
• When the liftgate or liftglass has been opened without the use of the keyless entry system or without first being unlocked.
• When any door is opened without first being unlocked using the keyless entry transmitter.
• When the driver door is opened without being first unlocked using the driver door cylinder.
The components of the system are:
• The body control module
• The door ajar switches
• The driver door key cylinder switch
• The liftgate/liftglass ajar switch

Disarming an Armed System/Silencing an Alarm
If system arming has occurred, it must be disarmed.
Important: Manually unlocking the doors does not disable the content theft deterrent (CTD) armed mode. Also, disconnecting the battery or pulling fuses does not disable the armed mode, as the BCM stores the CTD status in memory.
To disarm the CTD system perform one of the following:
• Press the UNLOCK button on the keyless entry transmitter.
• Unlock the driver door using the door key cylinder.
• Insert a valid key into the ignition and start the vehicle.

Transmitter Programming
Important: All transmitters which are to be recognized by the remote control door lock receiver (RCDLR) must be programmed in a single programming sequence. If the system is placed in program mode it will erase all previously programmed transmitters upon the receipt of the programming signal from the first transmitter. Up to 4 transmitters can be programmed. Do not operate or program the transmitters in the vicinity of other vehicles that are in the keyless entry program mode. This prevents the programming of the transmitters to the incorrect vehicle.
Install a scan tool.
Use the scan tool in order to access programming: Vehicle Control System/Computer Integrating System/Module Setup/BCM/Program Key Fobs.
Press the START soft key on the scan tool.
Important: The scan tool must stay connected until all of the transmitters are programmed.
Press and hold the LOCK button and the UNLOCK button simultaneously on one transmitter. After a delay of 5-10 seconds, the scan tool will indicate that the transmitter is programmed.
Repeat the previous step in order to program up to 4 transmitters.
Remove the scan tool.
Operate the transmitter functions in order to verify correct system operation.

Inside the driver door latch, there is a switch for the key that tells the system, the key switch is on or off position but usually, the wires are cut or if you prefer open circuit.
BUT you didn't mention if you try to unlock the door with your key or with the keyless entry??
Can you unlock the driver's door with the inside switch if not look for door lock problems?

Hope it helps

Disarming an Armed System/Silencing an Alarm
If system arming has been requested by the keyless entry transmitter, it must be disarmed.
Important: Using the power door unlock switch or manually unlocking the doors does not disable the CTD armed mode. Also, disconnecting the battery or pulling fuses does not disable the armed mode, since the BCM stores the CTD mode status in memory.
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To disarm the CTD system in arm pending mode, SECURITY indicator flashing and doors open, perform 1 of the following:

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Press the UNLOCK button on the keyless entry transmitter.

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Insert a valid key into the ignition and start the vehicle.

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To disarm the CTD system in the armed mode:

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Press the UNLOCK button on the keyless entry transmitter.

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Insert a valid key into the ignition and start the vehicle.

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To disarm the CTD system when activated, alarming mode.

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Press the UNLOCK button on the keyless entry transmitter.

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Insert a valid key into the ignition and start the vehicle.

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Try this

2004 XL7

1. Remove key from ignition switch.

2. Close all doors.

3. Open drivers door

4. Insert key and turn to ON position and within 10 seconds turn
key off and remove key.

5. Within 20 seconds Close and open drivers door 3 times.

6. Insert key and turn to ON position and within 10 seconds turn
key off and remove key.

7. Locks should now lock and unlock automatically to confirm you
have entered programming mode.

8. Press the UNLOCK button on remote and locks should cycle to
confirm programming.

9. Repeat step 8 on each additional remote.

10. Exit vehicle with keys and remote, close door test remote(s)

Programming
When
Remote control added or replaced. System malfunction.
How
Obtain all remote controls. Remove key from ignition switch. Close all doors. Open driver's door. Carry out the following within 24 seconds: Turn ignition switch ON and back to LOCK position 3 times. Remove key. Press and release driver's door courtesy light switch 3 times. Ensure doors lock and unlock. If not, wait 40 seconds and repeat procedure starting with driver's door already open. Press each remote control lock or unlock button twice. Ensure doors lock and unlock after each remote control operation. If not, proceed as follows: Press and release driver's door courtesy light switch once. Ensure doors lock and unlock twice. Repeat procedure starting with driver's door already open.
NOTE: A maximum of 3 remote controls can be programmed.

KEYLESS ENTRY SYSTEM With the keyless entry keypad, you can: • lock or unlock the vehicle doors without using the key. Your vehicle has a factory set 5 digit code that operates the keyless entry system. You can also program your own 5 digit personal entry code. The factory-set code is located: • on the owner's wallet card in the glove compartment • or at your dealer. When pressing the controls on the keyless entry keypad, press the middle of the controls to ensure a good activation. This system will disable the power door lock controls. These will not work until the vehicle is disarmed. Programming your own personal entry code To program your own code: 5. Enter factory set code (keypad will illuminate when pressed). 6. Press 1/2 control within five seconds of step 1. 7. Enter your personal 5 digit code. Enter each digit within five seconds of previous one. 8. After the code is entered, the locks will cycle, confirming that the new code has been set. Do not set a code that includes five of the same number or presents them in sequential order. Thieves can easily figure out these types of codes. Your personal code does not replace the permanent code that the dealership gave you. You can use either code to unlock your vehicle. If a second personal code is entered, the module will erase the first personal code in favor of the new code. Locks and Security 149 Locks and Security If you wish to erase your personal code, use the following instructions: 1. Enter factory set code. 2. Press 1/2 control and release. The system will now only respond to the factory set code. Anti-scan feature The anti-scan feature prevents repeated attempts at arriving at a valid key code. The keyless entry pad is disabled for 1 minute after 7 unsuccessful attempts (35 consecutive button presses) at entering a valid key code. The keypad will flash during this 1 minute mode. However, the 7/8 and 9/0 controls will still lock the vehicle. Anti-scan will be turned off after: • one minute of keypad inactivity. • the remote entry transmitter UNLOCK button is pressed. • the ignition is turned to the ON position. Unlocking the doors with the keyless entry system To unlock the driver door, enter either the factory set code or the personal code (each digit must be pressed within five seconds of the prior digit). The interior lamps will also illuminate. To unlock all doors, enter the factory set code or personal code (driver door unlocks) and press the 3/4 control within five seconds. Locking the doors with the keyless entry system It is not necessary to enter the factory or personal code prior to locking all doors. To lock the doors: • with the driver's door closed, press the 7/8 control and the 9/0 control at the same time.

I believe dealer has to re-program the new code.