Modes of Operation

Normal Mode 

During the operation of the throttle actuator control (TAC) system, several modes or functions are considered normal. The following modes may be entered during normal operation:

• Normal control with APP values-In this operating mode, the PCM controls throttle movement according to APP sensor input. This mode will continue until an error is detected in the APP sensor input or other critical data.
• Learned idle mode-When ever the powertrain control module (PCM) recognizes the learned idle throttle position (TP) value, the engine operates in the learned idle mode. In the learned idle mode, the PCM uses stored engine performance settings in order to provide the best quality idle for all idle speed situations.
• Cold engine start mode-The throttle valve has a default start position that ensures improved cold engine starting and cold engine operation.

Reduced Engine Power Mode 

When the PCM detects a condition with the TAC system, the PCM may enter a reduced engine power mode. If the condition that initiated the reduced power mode is corrected, normal throttle operation will return once the ignition has been turned OFF to ON. Reduced engine power can be enabled with the following conditions:

• Limited throttle mode-The PCM will continue to use the accelerator pedal for throttle control; however, vehicle acceleration is limited. In this mode at least one APP sensor signal is still deemed to be accurate.
• Limited throttle mode-The PCM has detected an error, but will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
• Forced idle mode-The PCM will perform the following actions:
  • Limits engine speed to near idle by cutting off the current to the throttle motor, leaving the throttle valve at the return spring idle position. The PCM will continue to use APP sensor input, but will only modify fuel and spark in order to maintain some driveability. This mode is entered when a fault is detected in either TP sensor or the TAC motor control system
  • Limits engine speed to idle because both APP sensor signals are determined to be erroneous.
• Traction Control or Stability Control mode-The PCM will temporarily disable throttle control from driver input, APP sensor input, in order to perform a traction or stability control action.
• Engine shutdown mode-The PCM will disable fuel and de-energize the TAC system.