Antenna - Keyless Entry: Description and Operation

Passive Entry Antenna







Description

Vehicles equipped with the optional Passive Entry (PE) or Keyless Go (KG) systems have several Low Frequency (LF), ferrite antenna units (1) located within the vehicle. Each ferrite PE antenna unit is contained within a molded black plastic housing with an integral connector receptacle (2) molded into one end. The connector receptacle contains terminal pins that connect the antenna to the vehicle electrical system through a twisted pair of conductors and a connector that are part of the adjacent body or instrument panel wire harness.

Each antenna housing also includes two integral mounting flanges (3) which can be used to mount the unit with screws. However, in some applications the antenna mounting flanges are riveted to a stamped metal adapter that serves as the LF antenna mounting bracket. This vehicle platform uses five PE antenna units. One is secured within the liftgate, one is secured to each quarter inner panel behind the C-pillar and one is secured to each front door hardware module carrier.

The antennas are each connected to the Passive Entry Module (PEM) on dedicated and sequentially numbered circuits. The left front door antenna is connected through the antenna 1 circuits, the right front door antenna is connected through the antenna 2 circuits, the left quarter inner panel antenna is connected through the antenna 3 circuits, the right quarter inner panel is connected through the antenna 4 circuits and the liftgate antenna is connected through the antenna 5 circuits.






An LF antenna unit cannot be adjusted or repaired. If ineffective or damaged, it must be replaced with a new unit. For applications where it is used, the antenna unit adapter or mounting bracket is serviced only as a unit with the LF antenna.

Operation

The Passive Entry (PE) antenna units allow the transmitter within the Passive Entry Module (PEM) to communicate via Low Frequency (LF) radio transmission with a FOB with Integrated Key (FOBIK) that is located inside the vehicle or, at most, about 2 meters (6.5 feet) horizontally in all directions around the outside of the vehicle. The PEM uses communication through the antenna units to wake up and challenge a FOBIK that is within range in order to authenticate whether that FOBIK is valid (programmed) to the vehicle. The PEM communication with the FOBIK is on 20 kilohertz using Frequency-Shift Keying (FSK) modulation.

Each antenna unit has two dedicated connections to the PEM. One connection is the LF antenna output circuit, while the other connection Is the LF antenna return circuit. These circuits to each antenna unit are a twisted pair to help reduce the potential for induced electrical interference. The PEM microprocessor continuously monitors all of the antenna units and will store a Diagnostic Trouble Code (DTC) for any fault that it detects.

The hard wired inputs and outputs of the antenna units may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, the most reliable, efficient, and accurate means to diagnose the antenna units requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.