Diagnostic Instructions

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	Open	High Resistance	Short to Voltage	Signal Performance
APP Sensor 1 Signal	P2122	P2122	P2138	P2123	P2138
APP Sensor 1 5-Volt Reference	P0698, P2122	P2122	P2138	P0401, P0699, P2123, P2565	P2138
APP Sensor 1 Low Reference	--	P2123	P2138	--	P2138
APP Sensor 2 Signal	P2127	P2127	P2138	P2128	P2138
APP Sensor 2 5-Volt Reference	P011A, P0117, P0462, P0522, P0652, P2127	P2127	P2138	P011A, P0118, P0653, P2128	P2138
APP Sensor 2 Low Reference	--	P2128	P2138	--	P2138

Typical Scan Tool Data

APP Sensor 1

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Ignition ON or Engine Running Parameter Normal Range: APP 1 Varies 0.90-4.35 V
APP Sensor 1 Signal	0 V	0 V	4.98 V
APP Sensor 1 5-Volt Reference	0 V	0 V	2.31 V
APP Sensor 1 Low Reference	--	4.94 V	--

APP Sensor 2

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Ignition ON or Engine Running Parameter Normal Range: APP 2 Varies 0.43-2.15 V
APP Sensor 2 Signal	0 V	0 V	4.98 V
APP Sensor 2 5-Volt Reference	0 V	0 V	1.14 V
APP Sensor 2 Low Reference	--	4.92 V	--

Circuit/System Description

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal control assembly. Two APP sensors, APP sensors 1 and 2 are used to monitor the accelerator pedal position. Each sensor has the following circuits:

The engine control module (ECM) uses the APP sensors input to determine the amount of acceleration or deceleration that is desired.

Conditions for Running the DTC

P2122 and P2123

P2127 and P2128

P2138

Conditions for Setting the DTC

P2122

The ECM detects that the APP sensor 1 voltage is less than 0.8 volt for greater than 0.2 second.

P2123

The ECM detects that the APP sensor 1 voltage is more than 4.75 volts for more than 0.2 second.

P2127

The ECM detects that the APP sensor 2 voltage is less than 0.3 volt for more than 0.2 second.

P2128

The ECM detects that the APP sensor 2 voltage is more than 2.5 volts for more than 0.2 second.

P2138

The voltage difference between APP sensor 1 and APP sensor 2 exceeds a value of 2 percent for more than 0.3 second.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

DTCs P2122, P2123, P2127, P2128, and P2138 are Type C DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Accelerator Pedal Position System Description

Electrical Information Reference

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 parameter for a normal voltage range between 0.80-4.75 volts.
2. Ignition ON, observe the scan tool APP Sensor 2 parameter for a normal voltage range between 0.30-2.50 volts.
3. Ignition ON, compare the scan tool APP Sensor 1 Indicated and APP Sensor 2 Indicated parameters. Verify they do not differ more than 2 percent during a full pedal sweep.
4. Operate the vehicle within the Conditions for Running the DTC to verify that 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 APP sensor. Allow at least 60 seconds for the ECM to power down.
2. Ignition OFF and scan tool disconnected for 90 seconds, test for less than 5 ohms of resistance between each low reference circuit terminals A and F, and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between each APP sensor 5-volt reference circuit terminals C and D, and ground.

⇒	If less than the specified range, test the affected 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Verify that the scan tool APP Sensor 1 and APP Sensor 2 parameters are less than 0.02 volt.

⇒	If greater than 0.02 volt, test the applicable signal circuit terminals B or E for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between each signal circuit terminals B or E and the 5-volt reference circuit. Verify that the scan tool APP Sensor parameter is greater than 4.57 volts.

⇒	If less than the specified range, test the applicable signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

6. Ignition OFF, disconnect the harness connectors X1 and X2 at the ECM.
7. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:

•	The ECM X2 signal circuit terminal 49 to APP terminal E

•	The ECM X1 signal circuit terminal 21 to APP terminal B

•	The ECM X1 5-volt reference circuit terminal 38 to APP terminal C

•	The ECM X2 5-volt reference circuit terminal 15 to APP terminal D

⇒	If greater than the specified range, repair the affected circuit for open/high resistance.

8. Test for infinite resistance between APP sensor 1 and 2 signal circuits.

⇒	If less than infinite resistance, repair the short between signal circuits.

9. If all circuits test normal, test or replace the accelerator pedal assembly.

Component Testing

Important: You must perform the Circuit/System Testing to verify the integrity of the APP circuits before proceeding with the Component Testing.

1. Ignition OFF, install a 3A fused jumper wire between the 5-volt reference circuit terminal of the affected APP sensor and 5 volts.
2. Install a jumper wire between the low reference circuit terminal and a ground.
3. Install a jumper wire at the signal circuit terminal of the affected sensor.
4. Ignition ON, sweep the sensor through the entire range while monitoring the voltage between the signal terminal jumper wire and the low reference terminal with a DMM. The voltage should vary between 0.80-4.75 volts for APP sensor 1 and 0.30-2.50 volts for APP sensor 2 without any spikes or dropouts.

⇒	If the voltage is not within the specified range or is erratic, replace the APP sensor assembly.

Repair Instructions

P2122, P2123, P2127 or P2128

Repair Verification

P2138

1. Install any components or connectors that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
3. Clear the DTCs.
4. Turn OFF the ignition for 90 seconds.
5. Duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
6. Engine running, observe the scan tool Soot Mass parameter. The value should be less than 30 grams.

⇒	If the Soot Mass value is greater than 30 grams, perform the Diesel Particulate Filter (DPF) Regeneration Enable.