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 P2122 00: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage
DTC P2123 00: Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage
DTC P2127 00: Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage
DTC P2128 00: Accelerator Pedal Position (APP) Sensor 2 Circuit High Voltage
DTC P2138 00: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
APP Sensor 1 Signal | P2122 00 | P2122 00 | P2123 00 | P2138 00
APP Sensor 1 5-Volt Reference | P2122 00 | P2122 00 | P2123 00 | --
APP Sensor 1 Low Reference | -- | P2123 00 | -- | --
APP Sensor 2 Signal | P2127 00 | P2127 00 | P2128 00 | P2138 00
APP Sensor 2 5-Volt Reference | P2127 00 | P2127 00 | P2128 00 | --
APP Sensor 2 Low Reference | -- | P2128 00 | -- | --

### Typical Scan Tool Data

#### APP Sensor 1

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The engine is operating at idle Parameter Normal Range: 0.13-4.88 V
APP Sensor 1 Signal | 0 V | 0 V | 5 V
APP Sensor 1 5-Volt Reference | 0 V | 0 V | 5 V
APP Sensor 1 Low Reference | -- | 4.96 V | --

#### APP Sensor 2

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The engine is operating at idle Parameter Normal Range: 0.12-2.64 V
APP Sensor 2 Signal | 0 V | 0 V | 5 V
APP Sensor 2 5-Volt Reference | 0 V | 0 V | 5 V
APP Sensor 2 Low Reference | -- | 4.92 V | --

### Circuit/System Description

The throttle actuator control (TAC) system uses two accelerator pedal position (APP) sensors to monitor the accelerator pedal position. The accelerator pedal position (APP) sensors 1 and 2 are located within the pedal assembly. Each sensor has a 5 V reference circuit, a low reference circuit, and a signal circuit.

Two processors are also used to monitor the throttle body (TAC) motor 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. The processors share and monitor data to verify that the indicated accelerator pedal position (APP) sensor calculation is correct.

### Conditions for Running the DTC

#### P2122 00, P2123 00, P2127 00, P212 008

• | The system voltage is greater than 7 V.

• | The ignition is in the unlock, accessory, run, or crank position.

• | DTC P0642 00, P0643 00, or P0606 00 is not set.

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

#### P2138 00

• | The system voltage is greater than 7 V.

• | The ignition is in the unlock, accessory or run position.

• | DTC P0642 00, P0643 00, P0606 00, P2122 00, P2123 00, P2127 00, or P2128 00 is not set.

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

### Conditions for Setting the DTC

#### P2122 00

The ECM detects that accelerator pedal position (APP) sensor 1 voltage is less than 0.63 V for greater than 0.5 s.

#### P2123 00

The ECM detects that accelerator pedal position (APP) sensor 1 voltage is greater than 4.588 V for greater than 0.5 s.

#### P2127 00

The ECM detects that accelerator pedal position (APP) sensor 2 voltage is less than 0.12 V for greater than 0.5 s.

#### P2128 00

The ECM detects that accelerator pedal position (APP) sensor 2 voltage is greater than 2.64 V for greater than 0.5 s.

#### P2138 00

The ECM detects that the difference between accelerator pedal position (APP) sensor 1 and accelerator pedal position (APP) sensor 2 exceeds a predetermined value for greater than 2 s.

### Action Taken When the DTC Sets

• | DTCs P2122 00, P2123 00, P2127, 00 P2128 00, and P2138 00 are Type A DTCs.

• | The ECM commands the throttle body (TAC) motor system to operate in reduced engine power mode.

### Conditions for Clearing the DTC

DTCs P2122 00, P2123 00, P2127 00, P2128 00, and P2138 00 are Type A DTCs.

### 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 Position parameter. The reading should be between 0.313-4.87 V, and change with the accelerator pedal input.
2. Ignition ON, observe the scan tool APP Sensor 2 Position parameter. The reading should be between 0.16-2.30 V, and change with the accelerator pedal input.
3. Ignition ON, observe the scan tool APP Sensor 1 Position and APP Sensor 2 Position parameter. The scan tool should indicate agree.
4. Clear the DTCs with the scan tool.
5. Operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.
6. Verify that the following DTCs are not set: DTC P0642 00, P043 00, and P2125 00.

⇒ | If DTCs P0642 00, P0643 00 are set, refer to LINK (DTC P0642 00, P0643 00).

### Circuit/System Testing

1. Ignition OFF for 90 s, disconnect the harness connector at the B107 Accelerator Pedal Position (APP) Sensor accelerator pedal.
2. Test for less than 3 Ω between each of the B107 Accelerator Pedal Position (APP) Sensor low reference circuit terminals 4 and 5 and ground.

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

3. Ignition ON, test for 4.8-5.2 V between each of the B107 Accelerator Pedal Position (APP) Sensor 5-volt reference circuit terminals 1 and 2 and ground.

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

⇒ | If greater than 5.2 V test affected 5-volt reference circuit for short to voltage. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

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

⇒ | If greater than 0.1 V, test the B107 Accelerator Pedal Position (APP) Sensor 1 and 2 signal circuits terminal 3 and 6 for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 2 of the B107 Accelerator Pedal Position (APP) Sensor 1, verify the APP sensor 1 voltage is greater than 4.8 V.

⇒ | If less than 4.8 V, test the B107 Accelerator Pedal Position (APP) Sensor 1 signal circuit for an open or short to ground. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

6. Install a 3A fused jumper wire between the signal circuit terminal 6 and the 5-volt reference circuit terminal 1 of the B107 Accelerator Pedal Position (APP) Sensor 2. Verify that the APP sensor 2 voltage is greater than 4.8 V.

⇒ | If less than 4.8 V, test the B107 accelerator pedal position (APP) sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

7. Ignition OFF for 90 seconds, disconnect the X 2 harness connector at the K20 Engine Control Module (ECM).
8. Test for less than 5 Ω on all B107 Accelerator Pedal Position (APP) Sensor circuits between the following terminals:

• | ECM low reference circuit terminal 26 (X2) to APP connector terminal 4

• | ECM low reference circuit terminal 27 (X2) to APP connector terminal 5

• | ECM signal circuit terminal 53 (X2) to APP connector terminal 6

• | ECM signal circuit terminal 54 (X2) to APP connector terminal 3

• | ECM 5-volt reference circuit terminal 24 (X2) to APP connector terminal 2

• | ECM 5-volt reference circuit terminal 25 (X1) to APP connector terminal 1

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

9. Test for infinite resistance between B107 Accelerator Pedal Position (APP) Sensor 1 signal circuit terminal 3 and B107 Accelerator Pedal Position (APP) sensor 2 signal circuit terminal 6.

⇒ | If less than infinite resistance, repair the short between B107 Accelerator Pedal Position (APP) Sensor 1 signal circuit and APP sensor 2 signal circuits.

⇒ | If all circuits test normal, replace the accelerator pedal.

### 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