Buick Regal: DTC P2122, P2123, P2127, P2128, or P2138

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 provide 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) Sensors 1-2 Not Plausible

Diagnostic Fault Information

Typical Scan Tool Data

APP Sensor 1

APP Sensor 2

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 V reference circuit, a low reference circuit, and a signal circuit.

Conditions for Running the DTC

P2122, P2123, P2127, P2128

• DTC P0697 and P06A3 are not set.
• The ignition is ON or the engine is running.
• The run/crank or powertrain relay voltage is greater than 6.0 V and reduced power is not active.
• DTC P2122, P2123, P2127, P2128 run continuously when the above conditions are met.

P2138

• DTC P0697, P06A3, P2122, P2123, P2127, and P2128 are not set.
• The ignition is ON or the engine is running.
• The run/crank or powertrain relay voltage is greater than 6.0 V and reduced power is not active.
• DTC P2138 runs continuously when the above conditions are met.

Conditions for Setting the DTC

P2122

The ECM detects the APP sensor 1 voltage is less than 0.46 V for greater than 1 s.

P2123

The ECM detects the APP sensor 1 voltage is greater than 4.75 V for greater than 1 s.

P2127

The ECM detects the APP sensor 2 voltage is less than 0.32 V for greater than 1 s.

P2128

The ECM detects the APP sensor 2 voltage is greater than 2.6 V for greater than 1 s.

P2138

The ECM detects the voltage difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for greater than 1 s.

Action Taken When the DTC Sets

• DTCs P2122, P2123, 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

DTCs P2122, P2123, 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.

Ensure that the in-line harness connector seals are installed correctly. Improper installation could result in water intrusion into the connector and cause a DTC to set.

Reference Information

Schematic Reference

Engine Controls Wiring Schematics (LTG)

Connector End View Reference

Component Connector End View Index

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.

2. Verify DTC P0697 or P06A3 is not set.

• If any of the DTCs are set

Refer to DTC P0641, P0651, P0697, P06A3, or P06D2 for further diagnosis.

• Go to next step: If none of the DTCs are set

3. Verify the scan tool APP Sensor 1 Circuit Status and APP Sensor 2 Circuit Status parameters display OK.

• If OK is not displayed

Refer to Circuit/System Testing.

• Go to next step: If OK is displayed

4. Verify the scan tool APP Sensor 1 and 2 parameter displays Agree while performing the tests listed below:

• Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release pedal. Repeat the procedure several times.
• Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times.
• If Disagree

Refer to Circuit/System Testing

• Go to next step: If Agree

5. Verify that DTC P2122, P2123, 2127, P2128, or P2138 is not set.

• If any of the DTCs are set

Refer to Circuit/System Testing

• Go to next step: If none of the DTCs set

6. 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.

7. Verify the DTC does not set.

• If the DTC sets

Refer to Circuit/System Testing

• Go to next step: If the DTC does not set

8. All OK

Circuit/System Testing

1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the B107 Accelerator Pedal Position Sensor. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 5 Ω between the appropriate low reference circuit terminal listed below and ground.

• APP sensor 1 low reference circuit terminal 4
• APP sensor 2 low reference circuit terminal 5
• If 5 Ω or greater

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for less than 2 Ω in the low reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• Go to next step: If less than 5 Ω

3. Ignition ON.

4. Test for 4.8 - 5.2 V between the appropriate 5 V reference circuit terminal listed below and ground.

• APP sensor 1 5 V reference circuit terminal 2
• APP sensor 2 5 V reference circuit terminal 1
• If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the 5 V reference circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the 5 V reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• If greater than 5.2 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the 5 V reference circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K20 Engine Control Module.

• Go to next step: If between 4.8 - 5.2 V

5. Verify the scan tool APP sensor 1 and APP sensor 2 voltage parameters are less than 0.3 V.

• If 0.3 V or greater

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the signal circuit terminal listed below and ground.

• APP sensor 1 signal circuit terminal 3
• APP sensor 2 signal circuit terminal 6
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K20 Engine Control Module.
• Go to next step: If less than 0.3 V

6. Install a 3 A fused jumper wire between the appropriate signal circuit terminal listed below and the 5 V reference circuit terminal 1.

• APP sensor 1 signal circuit terminal 3
• APP sensor 2 signal circuit terminal 6

7. Verify the scan tool APP sensor 1 or APP sensor 2 voltage parameter is greater than 4.8 V.

• If 4.8 V or less

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the signal circuit terminal and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• Go to next step: If greater than 4.8 V

8. Test or replace the B107 Accelerator Pedal Position Sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Accelerator Pedal with Position Sensor Assembly Replacement
• Control Module References for engine control module replacement, programming, and setup

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