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 provides 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 P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit
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 | P06A3, P2122 | P2138 | P2122 | P06A3, P2135 | P2138
Accelerator Pedal Position (APP) Sensor 1 Signal | P2122 | P2138 | P2122 | P06A3, P2123 | P2138
Accelerator Pedal Position (APP) Sensor 1 Low Reference | -- | P2138 | P2123 | -- | P2138
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit | P0107, P0697 | P2138 | P2127 | P0106, P0108, P0697 | P2138
Accelerator Pedal Position (APP) Sensor 1 Signal | P2122 | P2138 | P2122 | P06A3, P2123 | P2138
Accelerator Pedal Position (APP) Sensor 2 Low Reference | -- | P2138 | P2128 | -- | P2138

### Typical Scan Tool Data

#### APP Sensor 1 and 2

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The engine is operating at idle. Parameter Normal Range: APP Sensor 1 0.88-1.08 V Parameter Normal Range: APP Sensor 2 0.39-0.59 V
APP Sensor 1 5-Volt Reference | 0.00 V | 0.00 V | 2.75 V
APP Sensor 1 Signal | 0.00 V | 0.00 V | 4.98 V
APP Sensor 1 Low Reference | -- | 4.94 V | --
APP Sensor 2 5-Volt Reference | 0.00 V | 0.00 V | 1.35 V
APP Sensor 2 Signal | 0.00 V | 0.00 V | 4.98 V
APP Sensor 2 Low Reference | -- | 4.92 V | --

### 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 95 percent when fully depressed.

### Conditions for Running the DTC

#### P2122, P2123, P2127, or P2128

• | DTC P06A3 or P0697 are not set.

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

• | The ignition voltage is greater than 6 volts.

• | The ECM is not commanding reduced power.

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

#### P2138

• | DTCs P06A3, P0697, P2122, P2123, P2127, or P2128 are not set.

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

• | The ignition voltage is greater than 6 volts.

• | The ECM is not commanding reduced power.

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

### Conditions for Setting the DTC

#### P2122

The ECM detects that the APP sensor 1 voltage is less than 0.46 volt for less than 1 second.

#### P2123

The ECM detects that the APP sensor 1 voltage is greater than 4.7 volts for less than 1 second.

#### P2127

The ECM detects that the APP sensor 2 voltage is less than 0.32 volt for less than 1 second.

#### P2128

The ECM detects that the APP sensor 2 voltage is greater than 2.6 volts for less than 1 second.

#### P2138

The ECM detects that APP sensor 1 and APP sensor 2 disagree greater than 10 percent for less than 1 second.

OR

The ECM detects that both APP sensor 1 and APP sensor 2 are 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.

### 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.

• | A high resistance condition on the accelerator pedal position circuits could cause a DTC to set.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component 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

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify DTCs P0697 or P06A3 are not set.

⇒ | If a DTC is set, refer to DTC P0641, P0651, P0697, or P06A3.

2. Ignition ON, observe the scan tool APP Sensor 1 and 2 Indicated parameters. Both parameters should be 0 percent.
3. Observe the scan tool APP sensor 1 and 2 Agree/Disagree parameter while performing the following tests:

• | 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.

• | The APP sensor 1 and 2 Agree/Disagree parameter should display Agree.

4. Observe the DTC information with a scan tool. DTCs P2122, P2123, P2127, P2128, or P2138 should not set.
5. 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 you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the accelerator pedal assembly.
2. Ignition OFF for 1 minute, test for less than 5 Ω between the low reference circuit terminals listed below and ground.

• | Low reference circuit terminal 2

• | Low reference circuit terminal 4

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

3. Ignition ON, test for 4.8-5.2 V between both 5-volt reference circuit terminals listed below and ground.

• | 5 volt reference circuit terminal 5

• | 5 volt reference circuit terminal 6

⇒ | If less than the specified range, test the appropriate 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 APP sensor voltage parameter is at 0 V.

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

• | APP sensor 1 signal circuit terminal 3

• | APP sensor 2 signal circuit terminal 1

5. Install a 3 A fused jumper wire between the appropriate signal circuit listed below and the 5-volt reference circuit terminal 6. Verify the appropriate APP sensor voltage parameter is greater than 4.8 V.

• | APP sensor 1 signal circuit terminal 3

• | APP sensor 2 signal circuit terminal 1

⇒ | 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.

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 ECM replacement, setup, and programming