The central door locking system provides for locking or unlocking of the doors, as well as single-stage and two-stage unlocking.

The following triggers are used to activate this system when locking the doors:

The following triggers are used to activate the system when unlocking the doors:

Using a scan tool or the instrument cluster MFD, the body control module (BCM) can be programmed to operate in either two-stage or single-stage unlock, based on the instrument cluster MFD owner/operator requirements. If a faulty circuit exists on either the lock or unlock signal inputs, the opposing input will continue to function independently. This enables the doors to be unlocked when a faulty circuit exists on the lock input, or vice versa. If the lock/unlock system is operated several times within a predetermined time period, the system times out. After a fixed time delay, the system re-activates as normal. This feature is designed to protect the door-locking actuator motors. NOTE: Central locking is inhibited while the ignition is switched on. The Theft Deterrent System also affects operation of this system.

SINGLE-STAGE UNLOCK: In single-stage unlock mode, when the remote coded key unlock button is pressed for 0.25 second or longer; the BCM unlocks both of the doors simultaneously.

TWO-STAGE UNLOCK: This mode can be enabled or disabled by the customer. In the two-stage unlock mode, pressing the remote coded key unlock button for 0.25 second sends a signal to the remote receiver. When the BCM receives the unlock request from the remote receiver, it unlocks the driver door only. If the BCM receives another unlock request (the remote coded key unlock button is pressed again for 0.25 second), the BCM unlocks the passenger door. If the remote coded key is pressed continuously for 0.5 second, the BCM unlocks both of the doors; first the driver door and then the passenger door.

Reversible motors controlled by body control module (BCM) relays operate the door locks. These relays apply battery voltage to one side of each motor and ground to the other side. The central door locking system operational phases include Lock to Unlock and Unlock to Lock.

The door locks can be activated to unlock by either:

Each door lock is fitted with a reversible electric motor that is mechanically coupled to a threaded shaft that moves the door locking mechanism up and down, together with the cam that operates a microswitch within the door lock actuator that controls the direction of the motor operation.

There are three BCM relays that control the operation of the door locks; these being:

NOTE: The BCM relay identified on the wiring diagrams as ALL DOORS DEAD LOCK relay is a feature not used in the MY 2004 Pontiac GTO. As far as the circuit operation is concerned, the relay always remains de-energized, with its common contact on X4-1 remaining grounded.

The Door Unlock relay is the controlling device that initiates the unlocking action. In its static state, both of the motor coil's connections are connected to battery ground via pin X1-5 on the lock through to X4-8 on the BCM. When unlocking is required, this means that the BCM has detected that an Unlocking action is required from either the Remote Coded Key buttons being pressed, the key being rotated in the door lock, or the internal door knob has been lifted upward from within the vehicle.

Once an unlock requirement has been detected, the BCM energizes the relay coil for approximately 750 milliseconds, which applies +12 volts to pin X1-2 on the lock actuator. Within 500 milliseconds of this occurring, the door locking motor moves from the lock position to the unlock position. Once it has reached its limit, the cam on the lock shaft activates its microswitch, which changes the X1-1 motor coil supply voltage over to a different supply connected to the All Door Lock relay. At this point, the motor stops rotating as it reaches its physical limit. Approximately 250 milliseconds later, the Door Unlock relay de-energizes, resulting in 0 V (ground) appearing across the terminals of the motor.

During the transition stage of the lock while door locking is in progress the BCM responds to a locking request by activating the All Door Lock relay for approximately 750 milliseconds. This then puts +12 volts on the lock's motor terminal X1-6 via internal wiring to produce reverse current flow to the motor through terminal X1-2 to the BCM's de-energized Door Unlock relay terminal X4-8. Once the motor has driven to its Lock position, the door lock cam then releases the microswitch, which prepares the motor coil circuit to again respond to the Unlock command. Some 250 milliseconds later, the All Door Lock relay de-energizes and the battery voltage is removed from the motor via door lock terminal X1-6.

If both vehicle doors are unlocked from the driver door-lock, this action connects body control module (BCM) terminal X4-16 to ground via either of these two switching circuits. This reduced voltage change at X4-16 is seen by the BCM as a Driver Door Unlock Request signal. The BCM then responds to that request by activating its internal Driver Door Unlock relay to commence opening the door. NOTE: Manually activating any unlock request circuit triggers both the driver and the passenger doors to be unlocked.

The Unlocking of the passenger door using the passenger door lock knob initially changes over the actuator's microswitch contact from X1-3 to X1-4, which connects body control module (BCM) terminal X4-5 to ground via circuit 194. This change in voltage on terminal X4-5 is seen by the BCM as a Passenger Door Unlock Request signal. When either the driver or passenger door unlock is requested at BCM terminal X4-5 or X4-16, this is seen by the BCM as a system unlock request. The BCM energizes both the internal driver and passenger Unlock relays for approximately 0.75 second. When these relay contacts close, battery voltage is applied to terminal X1-2 of the door-lock motor coil, which drives the lock to the Unlock position. Terminal X1-1 of the door-lock actuators connects to BCM terminal X4-9 via the unused All Doors Deadlocked relay contact through BCM terminal X1-11 to ground. This action causes the door-lock actuators to move from the lock to the unlock position and the door-lock actuator switch contacts to change from terminals X1-1 to X1-6

Remote locking of the vehicle is accomplished in either one or two stages using the remote coded key. If the body control module (BCM) is operating in the two-stage unlock mode and the remote coded key Unlock button is pressed for 0.25 second, the internal key data signals to the microprocessor within the BCM that it requires single stage unlocking to take place. The BCM then processes the signal to confirm that it has come from the correct key, and if correct, the Driver Door Unlock relay temporarily moves to the Unlock state for 0.75 second, thereby unlocking the driver door only. This represents the first of the two stages of door unlocking. If the same remote coded key Unlock button is again pressed for an additional 0.25 second, and the BCM detects this command, it temporarily closes the Passenger Door Unlock relay contact for 0.75 second to the Unlock state, which unlocks the passenger door. This completes the second stage of door unlocking. A faster method to achieve Stage 2 unlocking is to press the remote coded key Unlock button continuously for 0.5 second. The BCM then unlocks both doors simultaneously: first the driver door, followed shortly after by the passenger door.

If the body control module (BCM) is operating in the single-stage unlock mode and the remote coded key Unlock button is pressed for 0.25 second, the BCM energizes both the Driver Door Unlock relay and the Passenger Door Unlock relay to the unlock state for 0.75 second. Both doors will then unlock, completing single stage unlocking. If both vehicle doors are closed, they can be locked via the driver or passenger door button if the vehicle was occupied or by a single locking operation of the driver door-lock using the key from outside the vehicle. Either of these actions associated with moving the door actuator manually causes the Driver Door Lock Switch microswitch contact X1-5 to change from the Unlock terminal X1-3 to the Lock terminal X1-4, which connects BCM terminal X4-20 to ground via circuit 195. This change in voltage detected on BCM terminal X4-20 is seen by the BCM as a system Lock Request. A Lock Request signal received by the BCM causes the BCM to energize the internal All Doors Lock relay for approximately 0.75 second. The relay contact closes and applies battery voltage through terminal X4-10 of the BCM to terminal X1-6 of both the driver and passenger door-lock actuators. Terminal X1-2 of the passenger door actuator is connected to ground via BCM terminal X4-1 and the Passenger Door Unlock relay contacts. Terminal X1-2 of the driver door-lock actuator is connected to ground via BCM terminal X4-8 and the Driver Door Unlock relay contact. These connections energize the door-lock actuators, which moves the door-lock knobs to the Lock (down) position. This action changes the door actuator switch contacts from terminals X1-6 to terminals X1-1, which connects to a permanent ground via the unused All Doors Deadbolt relay.

When locking the doors using the remote coded key, the data received from the key signals the body control module (BCM) that door locking is required. If both doors are closed and the key is the correct key, the BCM then energizes the All Door-Lock relay, which then locks both of the doors. The BCM monitors the door locking process from the microswitch contact changes occurring on terminals X1-3 and X1-4 of both door lock actuators. If either door does not lock for some reason, either BCM terminal X4-16 or terminal X4-5 will remain low and this low voltage is seen by the BCM as an unsuccessful attempt by it to lock the doors. If the driver door has been detected by the BCM as being closed, then the BCM momentarily sounds the theft deterrent horns to alert the driver that door locking was unsuccessful.

The body control module (BCM) uses the driver doorjamb input signal to determine if the driver door is fully closed. When the door is not fully closed, the doorjamb switch grounds terminal X4-19 via circuit 746. This causes the voltage at terminal X4-19 to be pulled low to less than 0.2 volt, which is seen by the BCM as the driver door ajar input signal.

The BCM uses the passenger doorjamb input signal to determine if a passenger door is fully closed. If the passenger door is not fully closed, terminal X4-4 is grounded through circuit 745. This causes the voltage at terminal X4-4 to be pulled low to less than 0.2 volt, which is seen by the BCM as the passenger door ajar input signal.