P2123
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 accelerator pedal assembly contains two accelerator pedal position (APP) sensors. The APP sensors are mounted in the pedal assembly and are not serviceable. The APP sensors provide a signal voltage that changes relative to the position of the accelerator pedal. The Engine Control Module (ECM) supplies a separate 5 V reference and low reference circuit for each of the APP sensors.
Conditions for Running the DTC
P2120, P2122, P2123, P2125, P2127, P2128
* The system voltage is more than 5.23 volts.
* The ignition is in the Unlock/Accessory or Run position.
* DTC P0641 is not set.
* DTC P2120, P2122, P2123, P2125, P2127, P2128 runs continuously when the above conditions are met.
P2138
* The system voltage is more than 5.23 volts.
* The ignition is in the Unlock/Accessory or Run position.
* DTC P0641, P0651, P2120, P2125 are not set.
* DTC P2138 runs continuously when the above conditions are met.
Conditions for Setting the DTC
P2120
The APP sensor 1 voltage is less than 0.32 volt, or more than 4.75 volts for more than 0.4 second.
P2122
The ECM detects that the APP sensor 1 voltage is less than 0.32 volt for more than 0.4 second.
P2123
The ECM detects that the APP sensor 1 voltage is more than 4.75 volts for more than 0.4 second.
P2125
The APP sensor 2 voltage is less than 0.32 volt, or more than 4.75 volts for more than 0.4 second.
P2127
The ECM detects that the APP sensor 2 voltage is less than 0.32 volt for more than 0.4 second.
P2128
The ECM detects that the APP sensor 2 voltage is more than 4.75 volts for more than 0.4 second.
P2138
The voltage difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for more than 2 seconds.
Action Taken When the DTC Sets
* DTC P2120, P2122, P2123, P2125, P2127, P2128, and P2138 are type A DTCs.
* The control module commands the TAC system to operate in the Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions the control module commands the engine OFF.
Conditions for Clearing the MIL/DTC
DTC P2120, P2122, P2123, P2125, P2127, P2128, and P2138 are type A DTCs.
Diagnostic Aids
A high resistance condition on the accelerator pedal sensor circuits could cause a DTC to set.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Throttle Actuator Control (TAC) System Description (Throttle Actuator Control (TAC) System Description)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0641 or P0651 are not set.
• If a DTC is set, refer to DTC P0641 or P0651 (P0641) for further diagnosis.
2. Ignition ON, observe the scan tool APP Sensor 1 and 2 voltage parameters. Verify both of the APP sensor voltages are between 0.32-4.75 V.
3. Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release pedal. Repeat the procedure several times. DTCs P2120, P2122, P2123, P2125, P2127, P2128, or P2138 should not set.
4. Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times. DTCs P2120, P2122, P2123, P2125, P2127, P2128, or P2138 should not set.
5. Observe the scan tool APP Sensor 1 and 2 parameter. The scan tool should indicate Agree.
6. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC or within the conditions that you observed from the Freeze Frame/Failure Records.
7. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P2120 or P2125 are not the only APP sensor DTCs set.
• If DTC P2120 or P2125 are the only DTCs set, replace the ECM.
8. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the accelerator pedal. Allow sufficient time for the ECM to power down.
2. Ignition OFF, test for less than 5 ohm between the appropriate low reference circuit terminal listed below and ground.
* APP sensor 1 terminal 4
* APP sensor 2 terminal 5
• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.
3. Ignition ON, test for 4.8-5.2 V between the appropriate 5-volt reference circuit terminal listed below and ground.
* APP sensor 1 terminal 2
* APP sensor 2 terminal 1
• If less than the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit/connections test normal, replace the ECM.
• If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
4. Observe the scan tool APP sensor 1 voltage parameter. Verify the voltage is less than 0.3 V.
• If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit/connections test normal, replace the ECM.
5. Observe the scan tool APP sensor 2 voltage parameter. Verify the voltage is less than 0.3 V.
• If greater than the specified range, test the signal circuit terminal 6 for a short to voltage. If the circuit/connections test normal, replace the ECM.
6. Install a 3 A fused jumper wire between the APP sensor 1 signal circuit terminal 3 and the 5-volt reference circuit terminal 2. Verify the APP sensor 1 voltage parameter is greater than 4.8 V.
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.
7. Connect a 3 A fused jumper wire between the APP sensor 2 signal circuit terminal 6 and the 5-volt reference circuit terminal 1. Verify the APP sensor 2 voltage parameter is greater than 4.8 V.
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.
8. If all circuits/connections test normal, test or replace the Accelerator Pedal Position Sensor.
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