P2128

DTC P2122, P2123, P2127, P2128, or P2138

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

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

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

Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.






Typical Scan Tool Data






Circuit/System Description

The accelerator pedal assembly contains 2 accelerator pedal position (APP) sensors. The APP sensors are mounted to the accelerator pedal assembly and are not serviceable. The APP sensors provide a signal voltage that changes relative to pedal position. The engine control module (ECM) supplies each APP sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit.

The APP sensor 1 signal voltage increases as the pedal is depressed, from approximately 1 volt at rest to above 4 volts when fully depressed. The APP sensor 2 signal voltage increases as the pedal is depressed, from approximately 0.5 volt at rest to more than 2 volts with the accelerator pedal fully depressed.

Conditions for Running the DTC

DTCs P2122, P2123
* DTC P0641 is not set.
* The ignition is ON or the engine is operating.
* The DTCs run continuously when the above conditions are met.

DTCs P2127, P2128
* DTC P0651 is not set.
* The ignition is ON or the engine is operating.
* The DTCs run continuously when the above conditions are met.

DTC P2138
* The ignition is ON or the engine is operating.
* The DTC runs continuously when the above condition is met.

Conditions for Setting the DTC

P2122

The ECM detects that the APP sensor 1 voltage is less than 0.25 volt for less than 1 second.

P2123

The ECM detects that the APP sensor 1 voltage is greater than 4.8 volts for less than 1 second.

P2127

The ECM detects that the APP sensor 2 voltage is less than 0.25 volt for less than 1 second.

P2128

The ECM detects that the APP sensor 2 voltage is greater than 4.8 volts for less than 1 second.

P2138
* The ECM detects that APP sensor 1 and APP sensor 2 disagree more than 4.5 percent for less than 1 second.
OR
* The ECM detects that both APP sensor 1 and APP sensor 2 are 4.5 percent greater than the learned minimum position for less than 1 second.

Action Taken When the DTC Sets

DTCs P2122, P2123, P2127, P2128, and P2138 are type A DTCs.

Conditions for Clearing the DTC

DTCs P2122, P2123, P2127, P2128, and P2138 are type A DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics Electrical Diagrams

Connector End View Reference
* Engine Control Module (ECM) Connector End Views Engine Control Module (ECM) Connector End Views
* Engine Controls Connector End Views Engine Controls Connector End Views

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

Diagnostic Trouble Code (DTC) Type Definitions Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference
* Scan Tool Data List Scan Tool Data List
* Scan Tool Data Definitions Scan Tool Data Definitions
* Scan Tool Output Controls Scan Tool Output Controls

Circuit/System Verification

1. Ignition ON, observe the APP Sensor parameters with a scan tool. Verify both of the APP sensor voltages are between 0.4-4.5 volts.
2. 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 P2122, P2123, P2127, P2128, or P2138 should not set.
3. Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times. DTCs P2122, P2123, P2127, P2128, or P2138 should not set.
4. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of the accelerator pedal assembly.
2. Ignition OFF, test for less than 5 ohms of resistance between the appropriate low reference circuit of the APP sensor and ground.

• If greater than 5 ohms, test the low reference circuit of the APP sensor for a short to voltage, or an open/high resistance. If the circuit/connections test normal, replace the ECM.

Important: The 5-volt reference circuits are internally and externally connected at the ECM. Other component DTCs may be set. If other DTCs are set, review the electrical schematic and diagnose the applicable circuits and components.


3. Ignition ON, test for 4.8-5.2 volts between the appropriate 5-volt reference circuit of the APP sensor and ground.

• If less than 4.8 volts, test the 5-volt reference circuit of the APP sensor for a short to ground or open/high resistance. If the circuit/connections test normal, replace the ECM.

• If greater than 5.2 volts, test the 5-volt reference circuit of the APP sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.

4. Using a scan tool, verify the appropriate APP sensor voltage parameter is less than 0.3 volt.

• If greater than 0.3 volt, test the signal circuit of the applicable APP sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.

5. Install a 3-amp fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit of the APP sensor. Verify the APP sensor voltage parameter is greater than 4.8 volts.

• If less than 4.8 volts, test the appropriate signal circuit of the APP sensor for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.
• If both APP sensor voltage parameters display greater than 4.8 volts test the signal circuits of the APP sensors for a shorted together condition. If the circuit/connections test normal, replace the ECM.

6. If all circuits/connections test normal, test or replace the accelerator pedal assembly.

Component Testing

APP Sensor
1. Ignition OFF, disconnect the harness connector of the accelerator pedal assembly.
2. Measure for 1,160-1,175 ohms between the 5-volt reference and the low reference terminals of the applicable APP sensor.

• If the resistance is not within the specified range, replace the accelerator pedal assembly.

3. Measure the resistance between the signal terminal and the low reference terminal of the appropriate APP sensor. Sweep the APP sensor through the entire range. The resistance should vary without any spikes or dropouts between 1,530 and 630 ohms for APP sensor 1, and 3,060 and 252 ohms for APP sensor 2.

• If the resistance is not within the specified range or is erratic, replace the accelerator pedal assembly.

4. Apply 5 volts and ground to the applicable terminals of the APP sensor, and measure the voltage between the signal and the low reference terminals. Sweep the APP sensor through the entire range. The voltage should vary without any spikes or dropouts between 4.3-1.2 volts for APP sensor 1, and 0.5-2.4 volts for APP sensor 2.

• If the voltage is not within the specified range or is erratic, replace the accelerator pedal assembly.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification Diagnostic Repair Verification after completing the diagnostic procedure.


* Accelerator Pedal with Position Sensor Replacement Service and Repair
* Control Module References Control Module References for engine control module replacement, setup, and programming