P2127
DTC P2120, P2122, P2123, P2125, P2127, P2128, or P2138
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptors
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
Diagnostic Fault Information
Typical Scan Tool Data
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.
Conditions for Running the DTC
P2120, P2122, P2123, P2125, P2127, P2128
* The system voltage is greater than 5.23 volts.
* The ignition is in the Unlock/Accessory, Run, or Crank position.
* DTC P0641, P0651, or P0606 is not set.
* The DTCs run continuously when the above conditions are met.
P2138
* The system voltage is greater than 5.23 volts.
* The ignition is in the Unlock/Accessory or Run position.
* DTC P0641, P0651, P0606, P2120, P2122, P2123, P2125, P2127, or P2128 is not set.
* The DTC runs continuously when the above conditions are met.
Conditions for Setting the DTC
P2120
The ECM detects that APP sensor 1 voltage is less than 0.33 volt or greater than 4.59 volts for greater than 0.5 second.
P2122
The ECM detects that APP sensor 1 voltage is less than 0.33 volt for greater than 0.5 second.
P2123
The ECM detects that APP sensor 1 voltage is greater than 4.59 volts for greater than 0.5 second.
P2125
The ECM detects that APP sensor 2 voltage is less than 0.16 volt or greater than 2.30 volts for greater than 0.5 second.
P2127
The ECM detects that APP sensor 2 voltage is less than 0.16 volt for greater than 0.5 second.
P2128
The ECM detects that APP sensor 2 voltage is greater than 2.30 volts for greater than 0.5 second.
P2138
The ECM detects that the difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for greater than 0.5 second.
Action Taken When the DTC Sets
* DTCs P2120, P2122, P2123, P2125, P2127, P2128, and P2138 are Type A DTCs.
* The ECM commands the TAC system to operate in Reduced Engine Power mode.
Conditions for Clearing the DTC
DTCs P2120, P2122, P2123, P2125, P2127, P2128, and P2138 are Type A DTCs.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Throttle Actuator Control (TAC) System Description (Throttle Actuator Control (TAC) System Description)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool APP sensor 1 voltage parameter. The reading should be between 0.13-4.87 volts, and change with the accelerator pedal input.
2. Ignition ON, observe the scan tool APP sensor 2 voltage parameter. The reading should be between 0.13-4.87 volts, and change with the accelerator pedal input.
3. Ignition ON, observe the scan tool APP sensor 1 and 2 parameter. The scan tool should indicate agree.
4. Clear the DTCs with the scan tool.
5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
6. Verify that the following DTCs are not set: DTC P0641, P0651, P2120, and P2125.
• If either or both DTCs P2120 or P2125 are set and they are the only DTCs set, replace the ECM.
• If DTCs P0641 or P0651 are set, refer to DTC P0641 or P0651 (P0641).
Circuit/System Testing
1. Ignition OFF for 90 seconds, disconnect the harness connector at the accelerator pedal.
2. Test for less than 3 ohms of resistance between each low reference circuit terminals A and D and ground.
• If greater than 3 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.2 volts between each 5-volt reference circuit terminals C and F and ground.
• If less than 4.8 volts, test affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
• If greater than 5.2 volts, test affected 5-volt reference circuit for short to voltage. If the circuit tests normal, replace the ECM.
4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.
• If greater than 0.1 volt, test the APP sensor 1 and 2 signal circuits terminals B and E for a short to voltage. If the circuit tests normal, replace the ECM.
5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal F of the APP sensor 1, verify the APP sensor 1 voltage is greater than 4.8 volts.
• If less than 4.8 volts, test the APP sensor 1 signal circuit for an open or short to ground. If the circuit tests normal, replace the ECM.
6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C of the APP sensor 2. Verify that the APP sensor 2 voltage is greater than 4.8 volts.
• If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
7. Ignition OFF for 90 seconds, disconnect the harness connector at the ECM.
8. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:
* ECM X1 low reference circuit terminal 37 to APP connector terminal A
* ECM X1 low reference circuit terminal 36 to APP connector terminal D
* ECM X1 signal circuit terminal 47 to APP connector terminal E
* ECM X1 signal circuit terminal 49 to APP connector terminal B
* ECM X1 5-volt reference circuit terminal 35 to APP connector terminal C
* ECM X1 5-volt reference circuit terminal 33 to APP connector terminal F
• If greater than 5 ohms, repair the affected circuit.
9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.
• If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.
• If all circuits test normal, replace the accelerator pedal.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Accelerator Pedal Position Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming