Passive Entry Module - Operation
OPERATION
The microprocessor in the Passive Entry Module (PEM) contains the logic circuits and controls all of the features of the Passive Entry (PE) and Keyless Go (KG) systems. The PEM receives battery voltage on a fused B(+) circuit and is grounded at all times through a hard wired remote ground point. These connections allow the PEM to operate regardless of the ignition switch position and with the IOD fuse removed.
The PEM has sufficient driver outputs to power a number of Low Frequency (LF) Radio Frequency (RF) antennas located within the vehicle, which it uses to communicate with up to eight different FOB with Integrated Key (FOBIK) units that have been programmed to the vehicle. The FOBIK units communicate with the PEM using Ultra High Frequency (UHF) communication on a frequency of 434 MegaHertz (MHz) using digital Frequency-Shift Keying (FSK) modulation with a 10 kilobyte rate for the PE and KG functionality.
The number of antennas and the specific antenna locations are designed to ensure complete vehicle interior coverage. The LF antennas are each numbered and connected to the PEM on dedicated and sequentially numbered circuits. This arrangement allows the PEM to localize the positions of transmitting FOBIK units using a triangulation strategy. See the WD Low Frequency Antenna And Circuit Numbering table.
The location of a valid FOBIK is critical to the PE and KG features that the PEM will allow. The PEM has the ability to distinguish that a FOBIK is inside or outside of the vehicle. Inside of the vehicle is defined as anywhere within the passenger compartment and up to 10 centimeters (4 inches) from the exterior surfaces of the vehicle. Outside of the vehicle is defined as anywhere within about 10 centimeters (4 inches) and about 1.5 meters (5 feet) and not to exceed 2 meters (6.5 feet) from the exterior surfaces of each unlock switch, but is further differentiated by zones.
The PEM identifies the zone in which the valid FOBIK is located as the active zone, which determines which vehicle aperture becomes accessible. This vehicle has three outside zones: outside left, outside right and outside rear. The PEM will not respond to an input from a zone that is not active. For example: If the outside left zone is active, the PEM will respond to inputs from the left front door smart handle, but not to inputs from the right front door smart handle or from the liftgate unlock switch.
The PEM provides voltage and a clean ground to power the logic circuits and switches of each of the smart exterior door handles. If a door handle Lock, Unlock or Hall Effect switch is approached or activated, the door handle logic uses current modulation to communicate the changed switch state over the same two circuits for the PEM to sense. If a valid key has been verified, the PEM will then send the appropriate electronic Lock or Unlock message to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. The PEM also senses the state of the liftgate Lock and Unlock switch located at the rear of the vehicle in the liftgate light bar, then uses the same logic and methodology to control access to that aperture.
When the PEM logic detects a PE input or KG request, the PEM and LF antennas challenge the FOBIK to identify whether it is a valid key. If a valid key is detected through the response from the FOBIK, the PEM sends the appropriate electronic message commands to other modules in the vehicle over the CAN data bus to enable an engine starting event, or to enable unlocking or locking of the appropriate vehicle aperture.
On vehicles so equipped, Remote Keyless Entry (RKE), Illuminated Entry, Remote Start, Vehicle Theft Alarm (VTA) and the Memory System each operate in the same manner with the PE and KG systems as without using either the factory default or preferred settings selected using the Customer Programmable Features function. If so desired, the PE system can also be disabled using the Customer Programmable Features function.
The PEM uses On-Board Diagnostics (OBD) and communicates with other modules in the vehicle as well as with a diagnostic scan tool using the Controller Area Network (CAN) data bus. This method of communication is used by the PEM to acquire vehicle configuration data, including customer programmable features. The PEM communicates with the Wireless Ignition Node (WIN) (also known as the Wireless Control Module/WCM or Sentry Key REmote Entry Module/SKREEM), the Powertrain Control Module (PCM) and the Totally Integrated Power Module (TIPM) (also known as the Forward Control Module/FCM) using the CAN data bus.
The PEM microprocessor monitors all of the PE and KG system circuits, then sets active and stored Diagnostic Trouble Codes (DTC) for any monitored system faults it detects. The PEM will also send electronic message requests to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) through the TIPM for the display of certain textual warning messages related to PE and KG system operation in the Electronic Vehicle Information Center (EVIC).
The hard wired inputs and outputs of the PEM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the PEM electronic controls or the communication between modules and other devices that provide some features of the PE and KG systems. The most reliable, efficient and accurate means to diagnose the PEM or the electronic controls and communication related to PE or KG system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.