Keyless Entry Transmitter
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
The keyless entry transmitters are not only used to passively or actively lock and unlock the vehicle, they are also used to allow vehicle starting. If the RCDLR does not receive a valid RF response after the transmitter is challenged, the RCDLR will not send a fuel enable message to the ECM. If the RCDLR is unable to establish communication with the transmitter during an attempted engine start, the ELECTRONIC KEY NOT DETECTED message will display on the driver information center (DIC).
When any one of the programmed key fobs are challenged by pressing the start button, it will passively send a RF signal to the RCDLR. The RCDLR will then send a serial data message to the ECM to enable engine starting.