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 P2121: Accelerator Pedal Position (APP) Sensor 1 Performance
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 | P0106, P0405, P2122, P2138 | P2121, P2138 | P2122, P2138 | P2123 | --
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit | P0122, P0222, P2122, P0532, P2119, P2127, P2135, P2138 | P0121, P0221, P2121,P2138 | P2127, P2138 | P0123, P0223, P2123 | --
Accelerator Pedal Position (APP) Sensor 1 Signal | P2122, P2138 | P2121, P2138 | P2122, P2138 | P2123 | P2121, P2138
Accelerator Pedal Position (APP) Sensor 2 Signal | P2127, P2138 | P2121, P2138 | P2127, P2138 | P2128 | P2121, P2138
Accelerator Pedal Position (APP) Sensor 1 Low Reference | -- | P2121, P2138 | P2123, P2138 | -- | --
Accelerator Pedal Position (APP) Sensor 2 Low Reference | -- | -- | P2128, P2138 | -- | --

### 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 1 Volts Parameter Normal Range: APP Sensor 2 0.5 Volts
5-Volt Reference | 0.00 Volts | 0.00 Volts | 5.00 Volts
APP Sensor 1 Signal | 0.00 Volts | 0.04 Volts | 5.00 Volts
APP Sensor 2 Signal | 0.00 Volts | 0.10 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 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 above 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 greater than 2 volts with the accelerator pedal fully depressed.

### Conditions for Running the DTCs

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

• | The ignition 1 voltage is greater than 8 volts.

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

### Conditions for Setting the DTC

#### P2121

• | The ECM detects the voltage difference between APP sensor 1, and APP sensor 2, is greater than a predetermined value.

• | The ECM detects that the APP sensor 1 voltage is greater than 1.5 volts.

#### P2122

The APP sensor 1 voltage is less than 0.89 volt for greater than 4 seconds.

#### P2123

The APP sensor 1 voltage is greater than 4.82 volts for greater than 4 seconds.

#### P2127

The APP sensor 2 voltage is less than 0.82 volt for greater than 4 seconds.

#### P2128

The APP sensor 2 voltage is greater than 4.82 volts for greater than 4 seconds.

#### P2138

• | The APP sensor 1 voltage is greater than 1.5 volts.

• | The ECM detects the voltage difference between the actual APP sensor 2, and the calculated APP sensor 2, is greater than a predetermined value.

### Action Taken When the DTC Sets

DTCs P2121, P2122, P2123, P2127, P2128, and P2138 are Type A DTCs.

### Conditions for Clearing the DTC

DTCs P2121, P2122, P2123, P2127, P2128, and P2138 are Type A DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Controls Connector End Views

• | Engine Control Module 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 APP Sensor parameters. Verify both of the parameters are between 0.4-4.5 volts.
2. 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 P2121, P2122, P2123, P2127, P2128, or P2138 should not set.
3. Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times. DTCs P2121, P2122, P2123, P2127, P2128, or P2138 should not set.
4. 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 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. 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 circuits test 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 greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuits test normal, replace the ECM.

⇒ | If less the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuits test normal, replace the ECM.

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

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

⇒ | If both scan tool APP sensor parameters display greater than 4.8 volts, test the signal circuits for being shorted together condition. If the circuits test normal, replace the ECM.

6. If all circuits test normal, 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