Circuit Description
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
When the Power Take-Off (PTO) switch is turned to the ON position and all PTO engage conditions are met, the engine RPM should increase to the standby speed. When the Powertrain Control Module (PCM) receives the signal from the PTO switch the PCM will send a signal to the Throttle Actuator Control Module (TAC). The TAC module controls the TAC motor which changes the position of the throttle. Communications between the two modules is monitored and checked for accuracy by the PCM. DTCs may be recorded in the event of the failure. The 6.6L diesel engine does not have a TAC system and the engine RPM is strictly controlled by the ECM and the Fuel Injection Control Module.