Abstract: Apparatus and method for detecting the connection of a trailer to a vehicle. The apparatus is connected to a pneumatic pressure line of the trailer's service braking system, and measures the pressure of the system to determine if the trailer is properly connected to the vehicle when the vehicle's engine is running. Further, the apparatus also contains an algorithm that monitors the signals from other vehicle systems, and uses that information to determine the trailer characteristics. The vehicle engine control system receives information from the apparatus and adjusts the various vehicle systems accordingly.