An H-bridge is an electronic circuit which enables a voltage to be applied across a load in either direction.
Modern automobile engines utilize an H-bridge to control the throttle motor. Using the H-bridge allows for accurate control in both directions. When testing, using a lab scope is best to determine if the signal is able to switch polarity correctly.
The term "H-bridge" is derived from the typical graphical representation of such a circuit. An H-bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4 (according to the first figure) are closed (and S2 and S3 are open) a positive voltage will be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor.
Using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through.
The video shows voltage change in an H-bridge circuit as used in an electronic throttle body.