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 Descriptor

DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

### Diagnostic Fault Information

Circuit | Short to Ground | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
APP Sensor 1 Signal | P2122 | P2122 | P2123 | P2138
APP Sensor 1 5V Reference | P2122 | P2122 | P2123 | --
APP Sensor 1 Low Reference | -- | P2123 | -- | --
APP Sensor 2 Signal | P2127 | P2128 | P2128 | P2138
APP Sensor 2 5V Reference | P2127 | P2127 | P2128 | --
APP Sensor 2 Low Reference | -- | P2128 | -- | --

### Typical Scan Tool Data

#### APP Sensor 1

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Parameter Normal Range: 0.13-4.87 V
APP Sensor 1 Signal | 0 V | 0 V | 5 V
APP Sensor 1 5V Reference | 0 V | 0 V | 5 V
APP Sensor 1 Low Reference | -- | 5 V | --

#### APP Sensor 2

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Parameter Normal Range: 0.13-4.87 V
APP Sensor 2 Signal | 0 V | 0 V | 5 V
APP Sensor 2 5V Reference | 0 V | 0 V | 5 V
APP Sensor 2 Low Reference | -- | 5 V | --

### Circuit/System Description

The throttle actuator control (TAC) system uses two accelerator pedal position (APP) sensors to monitor the accelerator pedal position. The APP sensors 1 and 2 are located within the pedal assembly. Each sensor has the following circuits:

• | A 5V reference circuit

• | A low reference circuit

• | A signal circuit

Two processors are also used to monitor the TAC system data. Both processors are located within the engine control module (ECM). Each signal circuit provides both processors with a signal voltage proportional to pedal movement. Both processors monitor each other's data to verify that the indicated APP calculation is correct.

### Conditions for Running the DTC

• | The system voltage is more than 7V.

• | The ignition is in the Unlock/Accessory or Run position.

• | The accelerator pedal is not in the rest position.

• | DTC P2138 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

The voltage difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for more than 2 seconds.

### Action Taken When the DTC Sets

• | DTC P2138 is a Type A DTC.

• | The control module commands the TAC system to operate in the Reduced Engine Power mode.

• | A message center or an indicator displays Reduced Engine Power.

### Conditions for Clearing the MIL/DTC

DTC P2138 is a Type A DTC.

### 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 scan tool APP sensor 1 voltage parameter. The reading should be between 0.84-4.82V and change with accelerator pedal input.
2. Ignition ON, observe the scan tool APP sensor 2 voltage parameter. The reading should be between 0.66-4.82V and change with accelerator pedal input.
3. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.
4. Verify that DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 are set:

⇒ | If DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698 or P0699 are set, refer to DTC P0641-P0643, P0651-P0653, or P0697-P0699.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B107 accelerator pedal position (APP) sensor. Allow sufficient time for the ECM to power down.
2. Test for less than 3Ω between each low reference circuit terminals 4 and 5 and ground.

⇒ | If greater than 3Ω, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.

3. Ignition ON, test for 4.8-5.2V between each 5V reference circuit terminals 1 and 2 and ground.

⇒ | If less than 4.8V, test affected 5V reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the K20 ECM.

⇒ | If greater than 5.2V, test affected 5V reference circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1V.

⇒ | If greater than 0.1V, test the APP sensor 1 and 2 signal circuits terminals 3 and 6 for a short to voltage. If the circuit tests normal, replace the K20 ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5V reference circuit terminal 2 of the APP sensor 1, and verify the APP sensor 1 voltage is greater than 4.8V.

⇒ | If less than 4.8V, test the APP sensor 1 signal circuit for an open, or short to ground. If the circuit tests normal, replace the K20 ECM.

6. Install a 3A fused jumper wire between the signal circuit terminal 6 and the 5V reference circuit terminal 1 of the APP sensor 2, and verify that the APP sensor 2 voltage is greater than 4.8V.

⇒ | If less than 4.8V, test the APP sensor 2 signal circuit for an open/high resistance, or short to ground. If the circuit tests normal, replace the control module.

7. Ignition OFF, disconnect the X2 harness connector at the K20 ECM.
8. Test for less than 5Ω on all APP sensor circuits between the following terminals:

• | The ECM X2 signal circuit terminal 15 to APP terminal 3

• | The ECM X2 signal circuit terminal 25 to APP terminal 6

• | The ECM X2 5V reference circuit terminal 48 to APP terminal 1

• | The ECM X2 5V reference circuit terminal 49 to APP terminal 2

⇒ | If greater than 5Ω, repair the affected circuit.

9. Test for infinite resistance between APP sensor 1 signal circuit terminal 3 and APP sensor 2 signal circuit terminal 6.

⇒ | If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuit.

10. If all circuits test normal, replace the B107 accelerator pedal position sensor.

### Component Testing

Note: Circuit/System Testing must be performed before proceeding with Component Testing.

#### Dynamic Test

1. Install a 3A fused jumper wire between the 5V reference terminal of the B107 accelerator pedal position sensor and 5V. Install a jumper wire between the low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the signal terminal and the low reference terminal with a DMM. the voltage should vary between 0.66-4.82V with out any spikes or dropouts.

⇒ | If the voltage is not within the specified range or is erratic, replace the B107 accelerator pedal position sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Accelerator Pedal Position Sensor Replacement

• | Control Module References