DTC P1125, P2120, P2125, or P2138: Accelerator Pedal Position (APP) System Diagnosis

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

• DTC P1125: Accelerator Pedal Position (APP) System
• DTC P2120: Accelerator Pedal Position (APP) Sensor 1 Circuit
• DTC P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit
• DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

Diagnostic Fault Information

Typical Scan Tool Data

APP Sensor 1

Operating Conditions: The engine is operating at idle

Parameter Normal Range APP Sensor 1: 0.24-4.49 V

APP Sensor 2

Operating Conditions: The engine is operating at idle

Parameter Normal Range APP Sensor 2: 0.24-4.49 V

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 the following circuits:

• A 5-volt reference circuit
• A low reference circuit
• A signal circuit

Conditions for Running the DTC

P1125

• DTCs P0606, P2108, and U0107 are not set.
• The ignition is ON.
• The communication between the TAC module and the powertrain control module (PCM) must be valid.

P2120 and P2125

• The system voltage is more than 5.23 volts.
• The ignition is in the Unlock/Accessory, Run, or Crank position.
• DTC P2107 is not set.
• The DTCs run 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 P2107 or P2108 is not set.
• The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

P1125

Two APP sensors are out of range, or both APP sensors disagree with each other.

P2120

• The APP sensor 1 voltage is less than 0.24 volt or more than 4.49 volts for more than 0.5 second. OR
• The APP sensor 2 5-volt reference voltage is less than 4.49 volts or more than 5.21 volts.

P2125

• The APP sensor 2 voltage is less than 0.24 volt or more than 4.49 volts for more than 0.5 second. OR
• The APP sensor 2 5-volt reference voltage is less than 4.49 volts or more than 5.21 volts.

P2138

The difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for more than 0.5 second.

Action Taken When the DTC Sets

• DTCs P1125, P2120, P2125, and P2138 are Type A DTCs.
• The control module commands the TAC system to operate in Reduced Engine Power mode.

Conditions for Clearing the DTC

DTCs P1125, P2120, P2125, and P2138 are Type A DTCs.

Reference Information

• Schematic Reference: Engine Controls Schematics
• Connector End View Reference: Component Connector End Views

Description and Operation

Throttle Actuator Control (TAC) System Description

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool APP sensor 1 voltage parameter. The reading should be between 0.24-4.49 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 0.24-4.49 volts, and change with the accelerator pedal input.
3. Ignition ON, observe the scan tool APP sensor 1 and 2 parameters. The scan tool should indicate agree.
4. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF for 90 seconds, disconnect the harness connector at the accelerator pedal.
2. Test for less than 3 ohms between each low reference circuit terminals A and D and ground.
   ⇒X If greater than 3 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the throttle body assembly.
3. Ignition ON, test for 4.8-5.2 volts between each 5-volt reference circuit terminals C and F and ground.
   ⇒X 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 throttle body assembly.
4. If greater than 5.2 volts, test affected 5-volt reference circuit for short to voltage. If the circuit tests normal, replace the throttle body assembly.
5. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.
   ⇒X 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 throttle body assembly.
6. 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.
   ⇒X 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 throttle body assembly.
7. 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.
   ⇒X 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 throttle body assembly.
8. Ignition OFF for 90 seconds, disconnect the harness connector at the throttle body assembly.
9. Test for less than 5 ohms on all APP sensor circuits between the following terminals:
   • Throttle body assembly low reference circuit terminal 2 to APP terminal A
   • Throttle body assembly low reference circuit terminal 12 to APP terminal D
   • Throttle body assembly signal circuit terminal 3 to APP terminal B
   • Throttle body assembly signal circuit terminal 11 to APP terminal E
   • Throttle body assembly 5-volt reference circuit terminal 1 to terminal C
   • Throttle body assembly 5-volt reference circuit terminal 13 to terminal F
   ⇒X If greater than 5 ohms, repair the affected circuit.
10. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.
11. If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.
12. If all circuits test normal, replace the accelerator pedal.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Accelerator Pedal Position Sensor Replacement
• Control Module References for PCM replacement, setup, and programming