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The throttle actuator control (TAC) system uses two accelerator pedal position (APP) sensors to monitor the accelerator pedal position. The APP sensors 1 and 2 are located within the pedal assembly. Each sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit.
Two processors are also used to monitor the TAC system data. Both processors are located within the engine control module (ECM). Each signal circuit provides both processors with a signal voltage proportional to pedal movement. The processors share and monitor data to verify that the indicated APP calculation is correct.
DTC P0455: Evaporative Emission (EVAP) System Large Leak
The control module tests the evaporative emission (EVAP) system for a large leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge solenoid valve OPEN and the EVAP vent solenoid valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge solenoid valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent solenoid valves.
Code p0320 refers to crank shaft position (CKP) sensor/engine speed RPM sensor-circuit malfunction===causes---wiring CKP/RPM sensor ---ECM. Get your hands on an aftermarket workshop manual for the car and you should be able to replace the items
Same 3 codes , p0455, p0442, & p2138 on my 2009 Chevy Impala and brought the car to a General Motor or Buick Dealer Service Department to replace vent solenoid or solenoid fuel tank evaporator control . Also replaced gas pedal position sensor.