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 | P0122, P0222, P0641, P2110, P2135 | P2138 | P2122 | P0223, P0641, P2106, P2110, P2135 | --
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit | P0107, P0405, P0452, P0651, P2077, P2106 | P2138 | P2106, P2127 | P0651 | --
Accelerator Pedal Position (APP) Sensor 1 Signal | P2122 | P2138 | P2122 | P2123 | P2138
Accelerator Pedal Position (APP) Sensor 2 Signal | P2127 | P2138 | P2127 | P2106, P2138 | P2138
Accelerator Pedal Position (APP) Sensor 1 Low Reference | -- | -- | 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% Parameter Normal Range: APP Sensor 2 0%
5-Volt Reference 1 | APP 1 0% | APP 1 0% | APP 1 14%
5-Volt Reference 2 | APP 2 0% | APP 2 0% | APP 2 4%
APP Sensor 1 Signal | APP 1 0% | APP 1 0% | APP 1 89%
APP Sensor 2 Signal | APP 2 0% | APP 2 0% | APP 2 189%
APP Sensor 1 Low Reference | -- | APP 1 88% | --
APP Sensor 2 Low Reference | -- | APP 2 186% | --

### 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.

Both the APP sensors 1 and 2 signal percentages increase as the pedal is depressed, from approximately 0 percent at rest to above 75 percent when fully depressed.

### Conditions for Running the DTC

#### P2122 or P2123

• | DTC P0641 is not set.

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

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

#### P2127 or P2128

• | DTC P0651 is not set.

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

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

#### P2138

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

• | The DTC runs continuously when the above condition is met.

### Conditions for Setting the DTC

#### P2122

The ECM detects that the APP sensor 1 voltage is less than 0.25 volt for less than 1 second.

#### P2123

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

#### P2127

The ECM detects that the APP sensor 2 voltage is less than 0.25 volt for less than 1 second.

#### P2128

The ECM detects that the APP sensor 2 voltage is greater than 4.8 volts for less than 1 second.

#### P2138

The ECM detects that APP sensor 1 and APP sensor 2 disagree greater than 4.5 percent for less than 1 second.

OR

The ECM detects that both APP sensor 1 and APP sensor 2 are 4.5 percent greater than the learned minimum position for less than 1 second.

### Action Taken When the DTC Sets

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

• | The ECM commands the TAC system to operate in a Reduced Engine Power mode.

• | The ECM commands the reduced engine power indicator ON.

#### P2122 or P2123

The ECM uses APP sensor 2 for accelerator pedal position.

#### P2126 or P2127

The ECM uses APP sensor 1 for accelerator pedal position.

#### P2138

The ECM uses the lowest position recorded from the APP sensors for accelerator pedal position.

### 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.

• | The scan tool 5 volt reference parameter should display between 4.8-5.2 volts.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify DTCs P0641 or P0651 are not set.

⇒ | If either DTC is set, refer to DTC P0641 or P0651 .

2. Ignition ON, observe the APP Sensor parameters with a scan tool. Verify both of the APP sensor percentage parameters are at 0 percent.
3. 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 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 List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of the accelerator pedal assembly.
2. Ignition OFF, test for less than 5 ohms of resistance between the appropriate low reference circuit of the APP sensor and ground.

⇒ | If greater than 5 ohms, test the low reference circuit of the APP sensor for a short to voltage, or an open/high resistance. If the circuit/connections 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, load test for 4.8-5.2 volts between the appropriate 5-volt reference circuit of the APP sensor and ground.

⇒ | If less than 4.8 volts, test the 5-volt reference circuit of the APP sensor for a short to ground or open/high resistance. If the circuit/connections test normal, replace the ECM.

⇒ | If greater than 5.2 volts, test the 5-volt reference circuit of the APP sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.

4. Using a scan tool, verify the appropriate APP sensor percentage parameter is at 0%.

⇒ | If greater than 0 percent, test the signal circuit of the applicable APP sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.

5. Install a 3A fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit of the APP sensor. Verify the APP sensor percentage parameter is greater than 85 percent.

⇒ | If less than the specified value, test the appropriate signal circuit of the APP sensor for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.

6. If all circuits/connections test normal, test or 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 ECM replacement, setup, and programming