Theory Of Operation
GENERAL OPERATION: The Electronic Throttle Control (ETC) Motor is controlled using an H-Bridge circuit inside the Powertrain Control Module (PCM). An H-Bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. The H-Bridge arrangement is generally used to reverse the polarity/direction of the Direct Current (DC) motor which allows the DC motor to run forward and backwards. The DC motor located in the Throttle Body drives the throttle blade. In order to decrease engine speed, along with spark and fuel delivery changes, the PCM commands the throttle blade closed reducing air flow into the engine and the engine speed decreases. In order to increase engine speed, the PCM commands the throttle blade open, increasing air flow and engine speed. On a normally functioning Throttle Body, the duty cycle of the ETC Motor should not go above approximately 40%. See the illustration below for a general configuration and operation of an H-Bridge:
ETC MOTOR DIAGNOSTICS: The PCM performs diagnostics on the DC Motor and circuits. If the PCM detects that the current draw or Pulse Width Modulation (PWM) to the DC Motor is too high or low for a calibrated period of time, then the PCM determines that the motor or circuitry is faulted and not operating properly.
The PCM can detect a circuit high or circuit low fault during operation of the component, whereas open circuit detection can only occur when the component is not being commanded. If an open occurs in the component or circuits during operation, the PCM will normally detect the failure during the performance diagnostic for the system that component is being used to control.