GM Service Manual Online
For 1990-2009 cars only

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 P2122: Accelerator Pedal Position Sensor 1 Circuit Low

DTC P2123: Accelerator Pedal Position Sensor 1 Circuit High

DTC P2127: Accelerator Pedal Position Sensor 2 Circuit Low

DTC P2128: Accelerator Pedal Position Sensor 2 Circuit High

DTC P2132: Accelerator Pedal Position Sensor 3 Circuit Low

DTC P2133: Accelerator Pedal Position Sensor 3 Circuit High

DTC P2138: Accelerator Pedal Position Sensor 1 and 2 Correlation

DTC P2139: Accelerator Pedal Position Sensor 1 and 3 Correlation

DTC P2140: Accelerator Pedal Position Sensor 2 and 3 Correlation

Diagnostic Fault Information

Circuit

Short to Ground

Open

Short to Voltage

APP 1 Sensor 5-Volt Reference

P0192, P02E8, P0409, P0462, P0642, P2453, P2454, P2564

P2122

--

APP 1 Sensor Signal

P2122

P2122

P2123

APP 1 Sensor GND

--

P2123

--

APP 2 Sensor 5-Volt Reference

P0652

P2127

--

APP 2 Sensor Signal

P2127

P2128

P2128

APP 2 Sensor GND

--

P2128

--

APP 3 Sensor 5-Volt Reference

P0698

P2132

--

APP 3 Sensor Signal

P2132

P2133

P2133

APP 3 Sensor GND

--

P2133

--

Typical Scan Tool Data

APP Sensor 1

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: APP 1 varies

Parameter Normal Range: 0-5 Volts

APP Sensor 1 5-Volt Reference

0 V

0 V

--

APP Sensor 1 Signal

0 V

0 V

5 V

APP Sensor 1 Low Reference

--

5 V

--

APP Sensor 2

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: APP 2 varies

Parameter Normal Range: 0-5 Volts

APP Sensor 2 5-Volt Reference

0 V

0 V

--

APP Sensor 2 Signal

0 V

5 V

5 V

APP Sensor 2 Low Reference

--

5 V

--

APP Sensor 3

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: APP 3 varies

Parameter Normal Range: 0-5 Volts

APP Sensor 3 5-Volt Reference

0 V

0 V

--

APP Sensor 3 Signal

0 V

5 V

5 V

APP Sensor 3 Low Reference

--

5 V

--

APP Sensor Normal Values

APP Sensor

Actual Pedal Position

(%) Depressed as Observed on a Scan Tool

Voltage as Observed on a Scan Tool

APP 1

Pedal at rest

0

0.52-0.80

APP 1

Pedal at full travel

100

2.12-2.78

APP 2

Pedal at reset

0

4.25-4.53

APP 2

Pedal at full travel

100

2.24-2.93

APP 3

Pedal at reset

0

3.95-4.13

APP 3

Pedal at full travel

100

2.96-3.16

Circuit/System Description

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of three individual sensors within one housing. The engine control module (ECM) uses the APP sensors to determine the amount of acceleration or deceleration desired by the person driving the vehicle via the fuel injector control. The ECM supplies 5 volts to the APP sensor on the 5-volt reference circuit. The ECM also provides a ground on the low reference circuit. The APP sensor provides a signal to the ECM on the APP sensor signal circuit, which is relative to the position changes of the accelerator pedal angle. The ECM monitors the APP sensor signal for voltages outside the normal range of the APP sensor.

Conditions for Running the DTC

P2122 and P2123

    • DTCs P0642 and P0643 are not set.
    • The battery voltage is between 10-16 volts.
    • The ignition switch is ON for longer than 2 seconds.

P2127 and P2128

    • DTCs P0652 and P0653 are not set.
    • The battery voltage is between 10-16 volts.
    • The ignition switch is ON for longer than 2 seconds.

P2132 and P2133

    • DTCs P0698 and P0699 are not set.
    • The battery voltage is between 10-16 volts.
    • The ignition switch is ON for longer than 2 seconds.

P2138

    • DTCs P0642, P0643, P0652 and P0653 are not set.
    • The ignition switch is ON.

P2139

    • DTCs P0642, P0643, P0698 and P0699 are not set.
    • The ignition switch is ON.

P2140

    • DTCs P0652, P0653, P0698 and P0699 are not set.
    • The ignition switch is ON.

Conditions for Setting the DTC

P2122, P2127 and P2132

The ECM detects that the APP sensor signal voltage is less than 0.25 volts.

P2123, P2128 and P2133

The ECM detects that the APP sensor signal voltage is more than 4.75 volts.

P2138

The ECM detects that the APP sensor 1 and 2 are more than 10 percent out of range of each other.

P2139

The ECM detects that the APP sensor 1 and 3 are more than 10 percent out of range of each other.

P2140

The ECM detects that the APP sensor 2 and 3 are more than 10 percent out of range of each other.

Action Taken When the DTC Sets

DTCs P2122, P2123, P2127, P2128, P2132, P2133, P2138, P2139 and P2140 are Type C DTCs.

Conditions for Clearing the DTC

DTCs P2122, P2123, P2127, P2128, P2132, P2133, P2138, P2139 and P2140 are Type C DTCs.

Diagnostic Aids

       Important: If DTCs P0642, P0643, P0652, P0653, P0698 and P0699 are set, test and repair those DTCs first.

    • Verify the integrity of the accelerator pedal, accelerator pedal position (APP) sensor by inspecting for the following conditions:
    • Inspect for any recent engine mechanical repairs. An incorrectly installed APP sensor will cause this DTC to set.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

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

    • Damaged components
    • Loose or improper installation

Circuit/System Testing

Important: You must perform Circuit/System Verification before proceeding with Circuit/System Testing.

  1. Ignition OFF, disconnect the harness connector at the APP sensor. Allow at least 60 seconds for the ECM to power down. Using a DMM, measure the voltage between the 5-volt reference circuit and a low reference circuit.
  2. If less than 4.8 volts, test the low reference circuit for an open/high resistance.
  3. Ignition OFF, test for 4.8-5.2 volts between the applicable APP sensor 5-volt reference circuit and ground.
  4. If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
    If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
  5. Install a 3A fused jumper wire between the applicable signal circuit and the applicable 5-volt reference circuit for APP sensor 2 and 3. Verify that the scan tool accelerator position (APP) sensor parameter is greater than 5 volts.
  6. If less than 4.8 volts, test the applicable signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
    If more than 5.2 volts, replace the accelerator pedal assembly.
  7. Install a 3A fused jumper wire between the applicable signal circuit and the applicable 5-volt reference circuit for APP sensor 1. Verify that the DMM volt meter scan tool accelerator position (APP) sensor parameter is greater than 5 volts.
  8. If less than 4.8 volts, test the applicable signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
    If more than 5.2 volts, replace the accelerator pedal assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Accelerator Pedal Position Sensor Replacement
    •  Control Module References for engine control module (ECM) replacement, setup, and programming