The TPS is a potentiometer used to indicate how much acceleration the driver needs. This has a 5-volt reference power and emits a ground signal, which comes from the PCM (Powertrain Control Module).
The sensor is used by the PCM to control both the delivery of fuel, and to operate the automatic transmission. A general measure is: At rest: 0.5 volts; and at full speed: 4.5 volts. If the PCM verify the angle of this accelerator is less or greater than that needed for a specific RPM (Revolutions Per Minute), the DTC code P0121 is established.