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 | P0343, P0348, P0368, P0393, P0652, P2122 | P2122, P2138 | P2122 | P0653, P2138, P2123 | P0652, P0653, P2138
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit | P0122, P0222, P0335, P0642, P0698, P0700 | P2127, P2138 | P2127 | P0123, P0221, P0699, P2138, P2128, P0700 | P0698, P0699, P2138
Accelerator Pedal Position (APP) Sensor 1 Signal | P2122 | P2138 | P2122 | P2123 | P2138
Accelerator Pedal Position (APP) Sensor 2 Signal | P2127 | P2138 | P2127 | P2128 | P2138
Accelerator Pedal Position (APP) Sensor 1 Low Reference | -- | P2123, P2138 | P2123 | -- | P2138
Accelerator Pedal Position (APP) Sensor 2 Low Reference | -- | P2127, P2138 | 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 0%/1 Volts Parameter Normal Range: APP Sensor 2 0%/0.5 Volts
5-Volt Reference | 0%/0.00 Volts | 0%/0.00 Volts | 0%/4.98 Volts
APP Sensor 1 Signal | 0%/0.00 Volts | 0%/0.00 Volts | 0%/4.98 Volts
APP Sensor 2 Signal | 0%/0.00 Volts | 0%/0.00 Volts | 0%/4.98 Volts
APP Sensor 1 Low Reference | -- | 0%/4.98 Volts | --
APP Sensor 2 Low Reference | -- | 0%/4.98 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 approximately 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 approximately 2 volts with the accelerator pedal fully depressed.

### Conditions for Running the DTCs

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

• | The ignition voltage is more than 7 volts.

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

### Conditions for Setting the DTC

#### P2122

The APP sensor 1 voltage is less than 0.86 volts for more than 200 milliseconds.

#### P2123

The APP sensor 1 voltage is more than 4.82 volts for more than 200 milliseconds.

#### P2127

The APP sensor 2 voltage is less than 0.63 volts for more than 200 milliseconds.

#### P2128

The APP sensor 2 voltage is more than 4.82 volts for more than 200 milliseconds.

#### P2138

• | The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 0.46 volts.

• | The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 0.58 volts with a partially pressed pedal.

• | The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 3.4 volts with a fully pressed pedal.

• | Any of the above conditions exist for more than 240 milliseconds.

### 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

Test the current out-put of the 5-volt reference circuits if you suspect high resistance in the circuit. The current out-put should be greater than 80 mA for APP 1 and greater than 50 mA for APP 2.

### 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. DTC P0652, P0653, P0698, or P0699 should not be set.

⇒ | If a DTC is set, refer to DTC P0652 or P0653 or DTC P0698 or P0699 .

2. Observe the APP Sensor voltage parameters with a scan tool. Verify both of the APP sensor voltages are between 0.4-4.5 volts.
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 Data List.

### Circuit/System Testing

1. Ignition OFF, remove the fuse that supplies B+ to terminal C2-56 of the ECM.
2. Disconnect the harness connector at the accelerator pedal assembly.
3. 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.

4. Install the fuse that supplies B+ to terminal C2-56 of the ECM.

Important: The 5-volt reference circuit voltage can be within the specified range with a high resistance in the circuit. If this condition is suspected, refer to Diagnostic Aids.

5. Ignition ON, test for 4.8-5.2 volts between the appropriate 5-volt reference circuit of the APP sensor and ground.

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

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

6. Observe the appropriate APP sensor voltage parameter with a scan tool. Verify the voltage is less than 0.3 volt.

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

7. 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 voltage parameter is greater than 4.8 volts.

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

⇒ | If both 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 circuit/connections test normal, replace the ECM.

8. If all circuits/connections test normal, test or replace the accelerator pedal assembly.

### Component Testing

1. Install a 3A fused jumper wire between the 5-volt reference terminal of the applicable APP sensor and 5 volts. Install a jumper wire between the applicable low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the appropriate signal circuit terminal and the low reference terminal with a DMM. The voltage for APP 1 should vary between 0.90-4.35 volts without any spikes or dropouts. The voltage for APP 2 should vary between 0.40-2.20 volts without any spikes or dropouts.

⇒ | If the voltage is not within the specified range or is erratic on either APP sensor, 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