The Complete Handbook of Motor Vehicle Controls

Chapter 1: Understanding Motor Vehicle Controls

Motor vehicle controls are the physical and logical interface between the operator's intent and the machine's response. This includes the pedals, levers, switches, and steering mechanisms, as well as the linkages, cables, hydraulic lines, and electronic signals that transmit that intent to the final actuation point. For the purposes of this handbook, the definition extends from the operator's hand or foot to the input device on the transmission, brake caliper, hydraulic valve, or throttle body. The steering wheel itself is a control, but so is the electronic control unit (ECU) that interprets the angle sensor and commands the electric power steering motor. Understanding this entire signal path is the difference between replacing a part that has failed and fixing a system that is not working.

To ground this in a concrete example, consider the throttle system on a modern passenger car. The driver depresses the accelerator pedal, which is not connected to the engine by a cable but rather to a pedal position sensor. This sensor generates a voltage or pulse-width modulated signal that travels over a twisted pair of wires to the engine control module. The ECU interprets this signal, cross-references it with the engine speed, gear position, and traction control logic, and then commands the electronic throttle body to open to a calculated angle. The throttle body receives this command via a second electrical signal, and an internal motor moves the butterfly valve. A feedback sensor inside the throttle body sends the