For 1990-2009 cars

### 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) Sensor 1-2 Correlation

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference Circuit | P0698 | P2138 | P2122 | P0123, P0223, P2123 | --
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit | P0698 | P2138 | P2127 | P0108, P2123 | --
Accelerator Pedal Position (APP) Sensor 1 Signal | P2122, P2138 | P2123, P2138 | P2122, P2138 | P2123 | P2138
Accelerator Pedal Position (APP) Sensor 2 Signal | P2127, P2138 | P2138 | P2127, P2138 | P2128 | P2138
Accelerator Pedal Position (APP) Sensor 1 Low Reference | -- | P2128, P2138 | P2123 | -- | --
Accelerator Pedal Position (APP) Sensor 1 Low Reference | -- | -- | P2128 | -- | --

### Typical Scan Tool Data

#### APP Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The engine is operating at idle. Parameter Normal Range: APP Sensor 1 0.7 Volts Parameter Normal Range: APP Sensor 2 0.3 Volts
5-Volt Reference | 0.00 Volts | 0.00 Volts | 5.00 Volts
APP Sensor 1 Signal | 0.00 Volts | 0.00 Volts | 5.00 Volts
APP Sensor 2 Signal | 0.00 Volts | 0.00 Volts | 5.00 Volts
APP Sensor 1 Low Reference | -- | 5.00 Volts | --
APP Sensor 2 Low Reference | -- | 5.00 Volts | --

### 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 0.7 volt at rest to above 4 volts when fully depressed. The APP sensor 2 signal voltage increases as the pedal is depressed, from approximately 0.3 volt at rest to more than 2 volts with the accelerator pedal fully depressed.

### Conditions for Running the DTC

#### P2122

• | DTCs P0642, and P0643 are not set.

• | The APP sensor 2 voltage is greater than 0.5 volt.

• | The ignition is ON or the engine is operating.

• | The DTC runs continuously once the above conditions are met.

#### P2123 or P2128

• | DTCs P0642, and P0643 are not set.

• | The ignition is ON or the engine is operating.

• | The DTCs run continuously once the above conditions are met.

#### P2127

• | DTCs P0642, and P0643 are not set.

• | The APP sensor 1 voltage is greater than 0.9 volt.

• | The ignition is ON or the engine is operating.

• | The DTC runs continuously once the above conditions are met.

#### P2138

• | The ignition is ON or the engine is operating.

• | The APP sensor 1 voltage is greater than 0.9 volt.

• | The DTC runs continuously once the above conditions are met.

OR

• | The ignition is ON or the engine is operating.

• | The APP sensor 2 voltage is greater than 0.5 volt.

• | The DTC runs continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P2122

The ECM detects that the APP sensor 1 voltage is less than 0.29 volt for less than 3 seconds.

#### P2123

The ECM detects that the APP sensor 1 voltage is greater than 4.8 volts for less than 3 seconds.

#### P2127

The ECM detects that the APP sensor 2 voltage is less than 0.17 volt for less than 3 seconds.

#### P2128

The ECM detects that the APP sensor 2 voltage is greater than 3.9 volts for less than 3 seconds.

#### P2138

The ECM detects that APP sensor 1 and APP sensor 2 disagree more than a calibrated amount for greater than 3 seconds.

### 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

If a shared 5-volt reference circuit is shorted to ground or shorted to a voltage, other 5-volt reference circuits may be affected.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Ignition ON, observe the scan tool DTC information parameter. Verify DTCs P0642 or P0643 are not set.

⇒ | If DTC P0642 or P0643 is set, refer to DTC P0642 or P0643 .

2. Ignition ON, verify both of the scan tool APP sensor voltage parameters are between 0.3-4.5 volts.
3. Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release the 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. 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 at the accelerator pedal assembly.
2. Ignition OFF for at least 20 seconds, test for less than 5 ohms of resistance between the appropriate low reference circuit and ground.

⇒ | If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests 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 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 tests normal, replace the ECM.

⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Verify the appropriate scan tool APP sensor voltage parameter is less than 0.3 volt.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit. Verify the scan tool 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 tests normal, replace the ECM.

⇒ | If both scan tool 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 circuits test normal, replace the ECM.

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

### Component Testing

1. Ignition OFF, disconnect the harness connector at the accelerator pedal assembly.
2. Measure for 1160-1175 ohms between the 5-volt reference terminal and the low reference terminal 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 1530 and 630 ohms for APP Sensor 1, and 3060 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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Accelerator Pedal Position Sensor Replacement

• | Control Module References for engine control module replacement, setup, and programming