Keyless Entry: Description and Operation

REMOTE KEYLESS ENTRY SYSTEM
A Remote Keyless Entry (RKE) system is on this model when it is equipped with the optional power lock system. The RKE system is a Radio Frequency (RF) system that allows the remote operation of the power lock system and, if the vehicle is so equipped, the Vehicle Theft Security System (VTSS).

The RKE system includes the following major components:
- Central Timer Module - The Central Timer Module (CTM) is located on the left cowl side inner panel under the driver side outboard end of the instrument panel. The CTM contains a microprocessor, an RF receiver, and the software that allow it to provide the many electronic functions and features of the RKE system.
- Keyless Entry Transmitter - The keyless entry transmitter is a small, battery-powered, RF transmitter that is contained within a molded plastic case that is designed to also serve as a convenient key fob.

Some additional features of the RKE system include:
- Driver Door Unlock Only - This is a programmable feature which allows the option of having a single press of the RKE transmitter Unlock button unlock only the driver door, or all doors. If the driver door only option is selected, a second press of the Unlock button will unlock the remaining doors.
- Horn Chirp - This feature provides a short, sharp chirp of the vehicle horn to give an audible confirmation that a valid Lock signal has been received from the RKE transmitter. This feature can be enabled or disabled and, if enabled, one of two optional horn chirp durations (20 or 40 milliseconds) can also be selected.
- Illuminated Entry - This feature turns ON the cargo lamp and courtesy lamps in the vehicle for a timed interval (about 30 seconds) each time a valid Unlock signal has been received from the RKE transmitter.
- Optical Chirp - This feature provides a flash of the vehicle park lamps to give an optical confirmation that a valid Lock or Unlock signal has been received from the RKE transmitter. The lamps flash once for a Lock signal, and twice for an Unlock signal. This feature can be enabled or disabled.
- Panic Mode - This feature allows the vehicle operator to cause the vehicle horn to pulse and headlights to flash for about 3 minutes, and the courtesy lamps to illuminate for about 30 seconds by depressing a Panic button on the RKE transmitter. Pressing the Panic button a second time will cancel the Panic mode. A vehicle speed of about 24 km/h (15 mph) will also cancel the panic mode.

Vehicles that are equipped with the Vehicle Theft Security System will also have the central locking feature. With the central locking feature, when the cylinder lock switch is turned to the LOCK position, all the doors will lock. For unlocking, if the key is turned to the UNLOCK position once, only that door will unlock. If the key is then turned a second time to the UNLOCK position within 4 seconds, all the doors will unlock.

There is also a door lock inhibit feature that prevents power locking of the doors if the ignition is OFF and the key is in the ignition. Automatic door locks, or "rolling locks", are included as a programmable feature. If the vehicle is moving approximately 15 mph and approximately 10 degrees of throttle opening is seen by the PCM (the PCM will send this info to the CTM via the PCI bus), indicating acceleration, the CTM will cycle the lock actuators to lock the doors.

On vehicles with the Remote Keyless Entry (RKE) system, the power locks can be operated remotely using the RKE transmitter. If the vehicle is so equipped, the RKE transmitter also arms and disarms the factory-installed Vehicle Theft Security System (VTSS). Three small, recessed buttons on the outside of the transmitter case labelled Lock, Unlock, and Panic allow the user to choose the function that is desired. The RKE transmitter then sends the appropriate Radio Frequency (RF) signal. An RF receiver that is integral to the Central Timer Module (CTM) receives the transmitted signal, which then uses its internal electronic programming to determine whether the received signal is valid and what function has been requested. If the signal is valid, the CTM then provides the programmed features.

Besides operating the power lock system and arming or disarming the VTSS, the RKE system also controls the following features:
- Driver Door Unlock Only - If this feature is enabled, the CTM unlocks only the driver side front door upon receipt of a first valid Unlock signal through a separate internal relay and control outputs to the driver side front door power lock motor. Then upon receipt of a second valid Unlock signal, the CTM unlocks all of the remaining doors through a separate internal relay and control circuits for those power lock motors.
- Horn Chirp - If this feature is enabled, the CTM provides a horn chirp by internally pulling the control coil of the horn relay to ground through a hard wired circuit output.
- Illuminated Entry - The CTM provides illuminated entry by internally controlling the current flow to the courtesy lamps and cargo lamp in the vehicle through a hard wired output circuit.
- Optical Chirp - If this feature is enabled, the CTM provides flashes of the park lamps by internally pulling the control coil of the park lamp relay to ground through a hard wired circuit output.
- Panic Mode - The CTM provides the horn pulse by internally pulling the control coil of the horn relay through a hard wired circuit output, then flashes the headlamps and illuminates the courtesy lamps through its internal high side control of these circuits. The CTM also monitors the vehicle speed through electronic messages it receives from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus network.

The RKE system operates on battery current received through a fused B(+) circuit from a fuse in the Junction Block (JB) so that the system remains functional, regardless of the ignition switch position. The RKE system can retain the vehicle access codes of up to four RKE transmitters. The transmitter codes are retained in RKE system memory, even if the battery is disconnected. If a transmitter is faulty or is lost, new transmitter vehicle access codes can be programmed into the system using a DRB III scan tool.

The RKE system is placed in the programming mode by the DRB III, or by the customer program features. The system will store up to four key fob codes. Two fobs are supplied with the truck; additional fobs may be purchased through the parts department. Through the DRB III, erasing and programming of one key fob without deleting the others is possible. If the key fob is stolen, all the fob codes stored previously may be erased to provide the owner of the vehicle with an extra sense of security.

Many of the electronic features in the vehicle controlled or supported by the CTM are programmable using the DRB III scan tool. If any of the CTM hardware components are damaged or faulty, the entire CTM unit must be replaced. The hard wired inputs or outputs of the CTM can be diagnosed using conventional diagnostic tools and methods; however, for diagnosis of the CTM or the PCI data bus, the use of a DRB III scan tool is required. Refer to the appropriate diagnostic information.