P2128

DTC P2122, P2123, P2127, P2128, or P2138

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



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






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-volt reference and low reference circuit for each of the APP sensors.


The APP sensor 1 signal voltage increases as the pedal is depressed, from approximately 1.0 volt at rest to approximately 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 approximately 2 volts with the accelerator pedal fully depressed.


Conditions for Running the DTCs

* The ignition is ON or the engine is operating.
* The ignition voltage is greater than 7 volts.
* The DTCs run continuously once the above conditions are met.



Conditions for Setting the DTC

P2122

The APP sensor 1 voltage is less than 0.86 volts for greater than 1 second.

P2123

The APP sensor 1 voltage is greater than 4.82 volts for greater than 1 second.

P2127

The APP sensor 2 voltage is less than 0.63 volts for greater than 1 second.

P2128

The APP sensor 2 voltage is greater than 4.82 volts for greater than 1 second.


P2138
* The ECM detects that the voltage difference between APP sensor 1 and 2 is greater than 0.46 volts.
* The ECM detects that the voltage difference between APP sensor 1 and 2 is greater than 0.58 volts with a partially pressed pedal.
* The ECM detects that the voltage difference between APP sensor 1 and 2 is greater than 3.4 volts with a fully pressed pedal.
* Any of the above conditions exist for greater 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.


Diagnostic Aids

Test the current output of the 5-volt reference circuits if you suspect high resistance in the circuit. The current output should be greater than 80 mA for APP 1 and greater than 50 mA for APP 2.


Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
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. DTC P0651, P0652, P0653, P0697, P0698, or P0699 should not be set.

• If a DTC is set, refer to DTC P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 (P0641) .

2. Observe the APP Sensor voltage parameters with a scan tool. Verify both of the APP sensor voltages are between 0.4-4.5 volts.
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 P2122, P2123, 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 P2122, P2123, P2127, P2128, or P2138 should not set.
5. 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, remove the fuse that supplies B+ to terminal X2-56 of the ECM.
2. Disconnect the harness connector at the accelerator pedal assembly.
3. Test for less than 5 ohms of resistance between the appropriate low reference circuit of the APP sensor and ground.

• If greater than the specified range, 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.

4. Install the fuse that supplies B+ to terminal X2-56 of the ECM.

Important: The 5-volt reference circuit voltage can be within the specified range with a high resistance in the circuit. If this condition is suspected, refer to Diagnostic Aids.


5. 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 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.

6. Observe the appropriate APP sensor voltage parameter with a scan tool. Verify the voltage is less than 0.3 volt.

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

7. Install a 3A 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 the specified range, test the appropriate signal circuit 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.

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



Component Testing

1. Install a 3A fused jumper wire between the 5-volt reference terminal of the applicable APP sensor and 5 volts. Install a jumper wire between the applicable low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the appropriate signal circuit terminal and the low reference terminal with a DMM. The voltage for APP 1 should vary between 0.90-4.35 volts without any spikes or dropouts. The voltage for APP 2 should vary between 0.40-2.20 volts without any spikes or dropouts.

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




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 engine control module replacement, setup, and programming