Accelerator position sensor 2 circuit low voltage

That vehicle doesn't have a IAC valve. That vehicle has TAC - electronic throttle control.

Throttle Actuator Control (TAC) System Description
Purpose
The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
• Accelerator pedal position (APP) sensing
• Throttle positioning to meet driver and engine demands
• Throttle position sensing
• Internal diagnostics
• Cruise control functions
• Manage TAC electrical power consumption
The TAC system includes the following components:
• The APP sensors
• The throttle body assembly
• The powertrain control module (PCM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal contains 2 individual accelerator pedal position (APP) sensors within the assembly. The APP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The APP sensors are used to determine the pedal angle. The powertrain control module (PCM) provides each APP sensor with a 5-volt reference circuit and a low reference circuit. The APP sensors provide the PCM with signal voltage proportional to the pedal movement. Both APP sensor signal voltages are low at rest position and increase as the pedal is applied.
Throttle Body Assembly
The throttle assembly contains the following components:
• The throttle blade
• The throttle actuator motor
• The throttle position (TP) sensor 1 and 2
• The throttle actuator control (TAC) module
The throttle body functions similar to a conventional throttle body with the following exceptions:
• There is no longer an idle air control (IAC) motor and associated air passages.
• An electric motor opens and closes the throttle valve.
• The TAC module is located within the throttle body assembly.
• The throttle blade is spring loaded in both directions and the default position is slightly open.
• There are 2 individual TP sensors within the throttle body assembly.
The TP sensors are used to determine the throttle plate angle. The TP sensors provide the powertrain control module (PCM) with a signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.

These codes appear to relate to your throttle poistion sensor(s) - check your throttle cable linkages and in particular the position sensor on the throttle body.

Switching on the aircon will rob the engine of a handful of horses but most people most of the time won't notice. Could be the problem goes deep.

By 2007 most vehicles were digital computer controlled so it isn't easy to guess what is going on. I think you need a guy with a good scanner who knows how to use it who can gather and interpret live data.

What is the DTC - diagnostic trouble code ? No code tells you a part is bad . Diagnostic testing procedures are given for each code the vehicle can set . Your vehicle can set numerous code's for the electronic throttle control an not one of them tell's you out right to replace the throttle body or the APP sensors . Looking at factory service repair info for the code an doing diagnostic testing befor replacing any parts should be done.

The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
• Accelerator pedal position sensing
• Throttle positioning to meet driver and engine demands
• Throttle position sensing
• Internal diagnostics
• Cruise control functions
• Manage TAC electrical power consumption
The TAC system components include the following:
• The accelerator pedal position (APP) sensors
• The throttle body assembly
• The throttle actuator control module
• The powertrain control module (PCM)

Accelerator Pedal Position (APP) Sensor
The accelerator pedal assembly contains 2 individual APP sensors within the assembly. The accelerator pedal position (APP) sensors 1 and 2 potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The APP sensors are used to determine the pedal angle. The control module provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors then provide the control module with signal voltage proportional to pedal movement. APP sensor 1 signal voltage is low at the rest position and increases as the accelerator pedal is applied. APP sensor 2 signal voltage is high at the rest position and decreases as the accelerator is applied.

Throttle Body Assembly
The throttle body assembly consists of the throttle body, the throttle position (TP) sensors, and the throttle actuator motor. The throttle body functions similar to a similar to a conventional throttle body with the following exceptions:
• An electric motor opens and closes the throttle valve.
• The throttle blade is spring loaded in both directions and the default position is slightly open.
• There are 2 individual TP sensors within the throttle body assembly.
The TP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The TP sensors are used to determine the throttle plate angle. The control module provides each TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensors then provide the control module with signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.

Your best bet , take it to a qualified repair shop.

Electronic throttle control !
DTC P2120: Accelerator Pedal Position (APP) Sensor 1 Circuit
DTC P2122: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage
DTC P2123: Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage
DTC P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit
DTC P2127: Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage
DTC P2128: Accelerator Pedal Position (APP) Sensor 2 Circuit High Voltage
DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

2009 Chevy Silverado P2138 Accelerator Pedal Position


Circuit/System Description
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.

DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation
Electronic throttle control problem .
The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
• Accelerator pedal position sensing
• Throttle positioning to meet driver and engine demands
• Throttle position sensing
• Internal diagnostics
• Cruise control functions
• Manage TAC electrical power consumption
The TAC system includes the following components:
• The accelerator pedal position (APP) sensors
• The throttle body assembly
• The engine control module (ECM)

Accelerator Pedal Position (APP) Sensor
The accelerator pedal contains 2 individual accelerator pedal position (APP) sensors within the assembly. The APP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The APP sensors are used to determine the pedal angle. The engine control module (ECM) provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors provide the ECM with signal voltage proportional to the pedal movement. The APP sensor 1 signal voltage at rest position is less than 1 volt and increases to more than 4 volts as the pedal is actuated. The APP sensor 2 signal voltage at rest position is less than 0.6 volt and increases to more than 2 volts as the pedal is actuated.
Search P2138 on youtube ,will show diagnostic steps .

First of all a scan tool is need for this not a code reader, you need to view scan data after you find what code is stored in the PCM. It could have a problem with the powertrain control module, wiring, or the Accelerator Pedal Position (APP) Sensors. Here are a few codes that could set .
DTC P2120: Accelerator Pedal Position (APP) Sensor 1 Circuit

DTC P2122: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage

DTC P2123: Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage

DTC P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit

DTC P2127: Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage

DTC P2128: Accelerator Pedal Position (APP) Sensor 2 Circuit High Voltage

DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

REDUCED POWER
Refer to:
• Powertrain Control Module Description for the 2.8L engine
• Powertrain Control Module Description for the 3.5L engine

Throttle Actuator Control (TAC) System
Throttle Actuator Control (TAC) Overview
The throttle actuator control (TAC) system uses vehicle electronics and components to calculate and control the position of the throttle blade. This eliminates the need for a mechanical cable attachment from the accelerator pedal to the throttle body. This system also performs the cruise control functions as well.
The TAC system components include, but are not limited to the following:
• The accelerator pedal position (APP) sensors
• The throttle body
• The powertrain control module (PCM)
Each of these components interface together to ensure accurate calculations and control of the throttle position.

Accelerator Pedal Position (APP) Sensor
The accelerator pedal position (APP) sensor is mounted on the accelerator pedal assembly. The APP is 2 individual APP sensors within one housing. There are 2 separate signal, low reference, and 5-volt reference circuits. APP sensor 1 voltage increases as the accelerator pedal is depressed. APP sensor 2 voltage decreases as the accelerator pedal is depressed.
Throttle Body Assembly
The throttle body for the throttle actuator control (TAC) system is similar to a conventional throttle body with several exceptions. One exception being the use of a motor to control the throttle position instead of a mechanical cable. Another exception is the throttle position (TP) sensor. The TP sensor is mounted in the throttle body assembly. The TP sensor is 2 individual TP sensors within the throttle body assembly. Two separate signals, low reference, and 5-volt reference circuits are used to connect the TP sensors and the powertrain control module (PCM). TP sensor 2 signal voltage increases as the throttle opens. TP sensor 1 signal voltage decreases as the throttle opens.

Reduced Engine Power Mode
When the PCM detects a problem with the throttle actuator control (TAC) system the PCM enters one of the following Reduced Engine Power Modes:
• Acceleration Limiting--The control module will continue to use the accelerator pedal for throttle control, however the vehicle acceleration is limited.
• Limited Throttle Mode--The control module will continue to use the accelerator pedal for throttle control, however the maximum throttle opening is limited.
• Throttle Default Mode--The control module will turn OFF the throttle actuator.
• Forced Idle Mode--The control module will perform the following actions:
- Limit engine speed to idle by positioning throttle position, or by controlling fuel and spark if throttle is turned OFF.
- Ignore accelerator pedal input.
• Engine Shutdown Mode--The control module will disable fuel and de-energize the throttle actuator.

Have you had it checked for DTC'S - diagnostic trouble codes ?

DTC P2176
The commanded throttle position (TP) is compared to the actual TP. Both values should be within a calibrated range of each other. The powertrain control module (PCM) continuously monitors the commanded and actual TPs. If the values are greater than the calibrated range, DTC P2176 sets.
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DTC P2138
The accelerator pedal position (APP) sensors 1 and 2 are located within the accelerator pedal assembly. Each sensor has the following circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
This provides the powertrain control module (PCM) with a signal voltage proportional to accelerator pedal movement. The APP sensor 1 signal voltage at rest position is near the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is near the 5-volt reference and decreases as the pedal is actuated.
DTC P2135
The throttle actuator control (TAC) assembly has 2 throttle position (TP) sensors mounted within the assembly. The powertrain control module (PCM) provides individual signal, ground, and 5-volt reference circuits to each sensor. Both sensors operate within a voltage range between 0.35-4.65 volts. When the throttle is opened from 0-100 percent, one sensor signal voltage increases while the other decreases. The signal circuit for TP sensor 1 is referenced to ground, and the signal circuit for TP sensor 2 is pulled up to 5 volts within the PCM.
DTC P2128
DTC P2127
DTC P2125
DTC P2123

Drive by Wire Function and diagnostics by Wells

Your vehicle has electronic throttle control . Position sensor's in the gas pedal an the throttle body , inputs to the Throttle Actuator Control Module
The TAC module is the control center for the throttle actuator control system. The TAC system is self-diagnosing and provides diagnostic information to the PCM through a dedicated serial data line. The TAC achieves throttle positioning by providing a pulse width modulated voltage to the TAC as directed by the PCM.

The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
• Accelerator pedal position sensing
• Throttle positioning to meet driver and engine demands
• Throttle position sensing
• Internal diagnostics
• Cruise control functions
• Manage TAC electrical power consumption
The TAC system components include the following:
• The accelerator pedal position (APP) sensors
• The throttle body assembly
• The throttle actuator control module
• The powertrain control module (PCM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal assembly contains 2 individual APP sensors within the assembly. The accelerator pedal position (APP) sensors 1 and 2 potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The APP sensors are used to determine the pedal angle. The control module provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors then provide the control module with signal voltage proportional to pedal movement. APP sensor 1 signal voltage is low at the rest position and increases as the accelerator pedal is applied. APP sensor 2 signal voltage is high at the rest position and decreases as the accelerator is applied.
Throttle Body Assembly
The throttle body assembly consists of the throttle body, the throttle position (TP) sensors, and the throttle actuator motor. The throttle body functions similar to a similar to a conventional throttle body with the following exceptions:
• An electric motor opens and closes the throttle valve.
• The throttle blade is spring loaded in both directions and the default position is slightly open.
• There are 2 individual TP sensors within the throttle body assembly.
The TP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
• A 5-volt reference circuit
• A low reference circuit
• A signal circuit
The TP sensors are used to determine the throttle plate angle. The control module provides each TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensors then provide the control module with signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.

Flickering light's could be caused by a bad diode in the alternator . Fluctuating idle could be caused same alternator problem or dirty throttle plate.
Throttle Body Cleaning To Restore Idle Quality

Hello, It should actually be an oil sending unit, and is located on the back of the intake manifold to the left of the distributor. *The P0523 is Oil Pressure Sending Unit Voltage too high *P1693 Generic fault indicating a fault in the bus or PCM/ECM interface *P1682 - I can't find this code Anyways, I will post here all the error codes for future reference. Dodge Cummins Check Engine Error Codes Cycle Key on-off-on-off-on to read codes in odometer display P0002 ECM fuel calibration error P0016 Crankshaft/Camshaft Timing Misalignment/Out-of- Sync P0071 Ambient Temperature Sensor Performance / Rationality P0072 Ambient Temperature Sensor Low P0073 Ambient Temperature Sensor High P0088 Fuel Rail Pressure Too High P0106 Manifold Absolute Pressure Sensor Performance / Rationality P0107 Manifold Absolute Pressure Sensor Low P0108 Manifold Absolute Pressure Sensor High P0111 Intake Air / Charge Temperature Sensor Performance / Rationality P0112 Intake Air / Charge Temperature Sensor Low P0113 Intake Air / Charge Temperature Sensor High P0116 Engine Coolant Temperature Sensor Performance / Rationality P0117 Engine Coolant Temperature Sensor Low P0118 Engine Coolant Temperature Sensor High P0121 Accelerator Position Sensor (APPS) Signal Voltage Too Low P0122 Accelerator Position Sensor (APPS) LowAPPS Voltage Input Too Low P0123 Accelerator Position Sensor (APPS) Signal Voltage Too High P0128 Cooling System Error / Thermostat Rationality P0148 Fuel Delivery Error P0168 Fuel Temp Too High P0169 Water-in-Fuel Detected For Too Long P0192 Fuel Rail Pressure Sensor Low P0193 Fuel Rail Pressure Sensor High P0201 Fuel Injector 1 Circuit P0202 Fuel Injector 2 Circuit P0203 Fuel Injector 3 Circuit P0204 Fuel Injector 4 Circuit P0205 Fuel Injector 5 Circuit P0206 Fuel Injector 6 Circuit P0216 Fuel Injection pump Timing Malfunciton [new injector pump time] P0217 Coolant Temperature Too High P0219 Engine Overspeed P0230 Transfer pump circuit out of range P0234 Turbocharger Overboost Condition P0235 Turbocharger Boost Sensor A Circuit P0236 Turbocharger Boost Pressure Sensor Performance / Rationality P0237 Turbocharger Boost Pressure Sensor Low P0238 Turbocharger Boost Pressure Sensor High P0251 Fuel Injection Pump Mechanical Failure Fuel Valve Feedback Circuit P0252 Injection Pump Fuel Metering Control "A" Range/Performance P0253 Fuel Injection Pump Fuel Valve Open Circuit P0254 Fuel Injection Pump Fuel Valve Current Too High P0300 Multiple Cylinder Misfire P0301 Cylinder 1 Misfire P0302 Cylinder 2 Misfire P0303 Cylinder 3 Misfire P0304 Cylinder 4 Misfire P0305 Cylinder 5 Misfire P0306 Cylinder 6 Misfire P0335 Crankshaft Position Sensor Circuit P0336 Crankshaft Position Sensor Performance P0337 Crankshaft Position Sensor Circuit Low P0338 Crankshaft Position Sensor Circuit High P0340 Camshaft Position Sensor Circuit P0341 Camshaft Position Sensor Performance / Rationality P0370 Timing Reference High Resolution Signal "A" P0380 Intake Air Heater #1 Control circuit P0381 Wait-to-Start Lamp Inoperative P0382 Intake Air Heater #2 Control circuit P0460 Fuel Level Sensor A Circuit P0461 Fuel Level Sensor 1 Performance / Rationality P0462 Fuel Level Sensor 1 Low P0463 Fuel Level Sensor 1 High P0477 Exhaust Pressure Control Relay Low P0478 Exhaust Pressure Control Relay High P0480 Cooling Fan 1 Control Circuit/Open (Low Speed Fan Relay) P0483 Cooling Fan Speed P0500 Vehicle Speed Sensor 1 Circuit, or No Vehicle Speed Reference Signal 1 P0514 Battery Temperature Sensor Performance / Rationality P0516 Battery Temperature Sensor Low P0517 Battery Temperature Sensor High P0521 Oil Pressure Sensor Performance / Rationality P0522 Engine Oil Pressure Sensor/Switch Circuit Low Input P0523 Oil Pressure Sending Unit Voltage too high P0524 Oil Pressure Too Low P0532 A/C Pressure Sensor Low P0533 A/C Pressure Sensor High P0541 Intake Air Heater Relay 1 Low P0542 Intake Air Heater Relay 1 High P0562 Battery Voltage Low P0563 Battery Voltage High P0572 Brake Switch 1 Low P0573 Brake Switch 1 High P0576 Cruise Control Input Circuit Low P0580 Speed Control Multiplexed Switch 1 Low P0581 Speed Control Multiplexed Switch 1 High P0602 Control Module Programming Error/NotProgrammed P0604 Internal Control Module RAM Integrity Failure P0606 Internal ECM Processor P0607 ECU Internal Performance P0622 Generator Field Control Circuit P0628 Fuel Pump Relay Circuit Low, or Fuel Lift Pump Control Circuit Low P0629 Fuel Pump Relay Circuit High, or Fuel Lift Pump Control Circuit High P0630 VIN Not Programmed in PCM P0633 SKIM Key Not Programmed in PCM P0642 Sensor Reference Voltage 1 Circuit Low P0643 Sensor Reference Voltage 1 Circuit High P0646 A/C Clutch Relay Circuit Low P0647 A/C Clutch Relay Circuit High P0652 Sensor Reference Voltage 2 Circuit Low P0653 Sensor Reference Voltage 2 Circuit High P0698 Sensor Reference Voltage 3 Circuit Low P0699 Sensor Reference Voltage 3 Circuit High P0700 Transmission Control System (MIL Request) P0743 Torque Converter Clutch Circuit Electrical P0753 Shift Solenoid "A" Electrical P0837 Four Wheel Drive (4WD) Switch Performance / Rationality P0838 Four Wheel Drive (4WD) Switch Circuit Low P0839 Four Wheel Drive (4WD) Switch Circuit High P1488 Auxiliary 5 volt supply output is too low P1492 Ambient/batt temp sensor volts too high P1493 Ambient/batt temp sensor volts too low P1596 Speed Control Switch always high P1597 Speed Control Switch always low P1652 J1850 Communication Bus P1687 No Cluster BUS Message or No Messages from the Mechanical Instrument Cluster P1688 Internal Fuel Injection Pump Controller Failure P1689 No Communication Between ECM & Injection Pump Module P1690 Fuel injection pump CKP Sensor Does Not Agree With ECM CKP Sensor P1691 Fuel Injection Pump Controller Calibration Failure P1693 Generic fault indicating a fault in the bus or PCM/ECM interface P1757 Governor pressure is above 3 PSI when 0 PSI is requested P1762 Governor Press Sensor Offset Volts Too Low or Too High P1765 Transmission 12 volt supply relay control circuit P2121 Pedal Position Sensor 1 Performance / Rationality P2122 Pedal Position Sensor 1 Low P2123 Pedal Position Sensor 1 High P2127 Pedal Validation Switch 2 Low P2128 Pedal Validation Switch 2 High P2146 Fuel Injector Group 1 Supply Voltage Circuit P2149 Fuel Injector Group 2 Supply Voltage Circuit P2266 Water in Fuel Sensor Circuit Low P2269 Water in Fuel Condition P2502 Charging System Output Voltage P2503 Charging System Output Low P2504 Charging System Output High P2509 ECM/PCM Power Input Signal Intermittent P2607 Intake Air Heater Relay 2 Low P2608 Intake Air Heater Relay 2 High P2609 Intake Air Heater System Performance Hope this will help you. Cheers! Ryan