A system and method providing truck-mounted sensors to detect trailer following vehicles and trailer conditions are disclosed. A system of an example embodiment comprises: a vehicle control subsystem installed in an autonomous truck, the vehicle control subsystem comprising a data processor; and a truck-mounted sensor subsystem installed on a portion of a tractor of the autonomous truck to which a trailer is attachable, the truck-mounted sensor subsystem being coupled to the vehicle control subsystem via a data connection, wherein the truck-mounted sensor subsystem is configured to emit electromagnetic waves propagating in a space under the trailer, to generate object data representing objects detected by receiving a reflection of the electromagnetic waves, and to transfer the object data to the vehicle control subsystem.