Abstract: Access to a motor vehicle is controlled by periodically transmitting an interrogation signal from a control circuit on the vehicle. Upon receiving the interrogation signal, a hand-held remote control transmits a reply signal to the control circuit. The control circuit measures the strength of the reply signal and the activates a first function, such as unlocking a door of the vehicle, when the strength exceeds a first threshold level. Thereafter, when the signal strength exceeds a second threshold level, the control circuit activates a second function, for example enabling the engine to be started. When the signal strength drops below a third threshold activates a third function, such as locking the door.

Abstract: A device on a motor vehicle is controlled by selecting a function for the device to perform. The selection is conveyed to a control circuit which wirelessly transmits a message using the Digital Enhanced Cordless Telecommunications protocol, wherein the message identifies the device and function. A controller receives the message and recovers the identification of the device and the function and then responds by activating the device to perform that function.

Abstract: A vehicle has a memory which stores operational data regarding the vehicle's performance. When the vehicle malfunctions the operational data can be transmitted from a control circuit in the vehicle by a radio frequency signal using the Digital Enhanced Cordless Telecommunications protocol. That radio frequency signal is received at a telephone and the operational recovered. The telephone transfers the operational data via a telephone network to diagnostic computer system which analyzes the operational data to diagnose the cause of the malfunction. The results of the diagnose can be transmitted back to the vehicle.