Circuit/System Description
WARNING: This page is about a different car, the 2008 Cadillac XLR. However, it is still accessible from the selected car via links, so may be relevant.
The back up keyless entry antenna is located in the glove compartment area and is used as a short range low frequency (LF) transmitter. When a valid key fob is within the passenger compartment and the brake pedal is depressed and the ignition button is pressed the keyless entry antenna transmitter broadcasts a challenge within the passenger compartment to the key fob. If the response from the key fob via radio frequency (RF) is a valid response and all the security requirement are met the vehicles engine will start or be able to go into accessory mode.