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	High Resistance	Open	Short to Voltage
APP Sensor 1 Signal	P2122	P2138	P2122	P0106, P2123, P2565
APP Sensor 1 5-Volt Reference	P2122, P0698	P0107, P2138, P2564	P2122	P0106, P0401, P0699, P2123, P2565
APP Sensor 1 Low Reference	--	P2138	P2123	--
APP Sensor 2 Signal	P2127	P2138	P2127	P2128
APP Sensor 2 5-Volt Reference	P0117, P0462, P0522, P0532, P0652, P2127	P2138	P2127	P2128, P0653
APP Sensor 2 Low Reference	--	P2138	P2128	--

Typical Scan Tool Data

APP Sensor 1

Circuit	Short to Ground	Open	Short to Voltage
Parameter Normal Range: APP 1 varies 0.90-4.35 V
APP Sensor 1 Signal	0 V	0 V	5 V
APP Sensor 1 5-Volt Reference	0 V	0 V	2.39 V
APP Sensor 1 Low Reference	--	5 V	--

APP Sensor 2

Circuit	Short to Ground	Open	Short to Voltage
Parameter Normal Range: APP 2 varies 0.43-2.15 V
APP Sensor 2 Signal	0 V	0 V	5 V
APP Sensor 2 5-Volt Reference	0 V	0 V	0.96 V
APP Sensor 2 Low Reference	--	5 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, P2123, P2127, P2128

P2138

Conditions for Setting the DTC

P2122

The ECM detects that the APP sensor 1 voltage is less than 0.8 volt for more 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

Description and Operation

Accelerator Pedal Position System Description

Electrical Information Reference

DTC Type Reference

Scan Tool Reference

Circuit/System Verification

1. Ignition ON, observe the scan tool APP sensor 1 parameter for a normal voltage range between 0.89-4.57 volts.
2. Ignition ON, observe the scan tool APP sensor 2 parameter for a normal voltage range between 0.41-2.19 volts.
3. Ignition ON, compare the scan tool APP sensors 1 and 2 parameters. Verify they do not differ more than 2 percent during a full pedal sweep.
4. Engine running, 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. You may also operate the vehicle within the conditions that you observed from the Freeze Frame 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 2 ohms of resistance between each low reference circuit terminals 1 and 6 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 3 and 4 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 Sensor 2 parameters are less than 0.02 volt.

⇒	If greater than 0.02 volt, test the applicable signal circuit terminals 2 or 5 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 2 or 5 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 connector at the ECM.
7. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:

•	The ECM C2 signal circuit terminal 49 to APP terminal 5

•	The ECM C1 signal circuit terminal 21 to APP terminal 2

•	The ECM C1 5-volt reference circuit terminal 38 to APP terminal 3

•	The ECM C2 5-volt reference circuit terminal 15 to APP terminal 4

⇒	If greater than 5 ohms, 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 the accelerator pedal assembly. Refer to Component Testing for instructions.

⇒	If the APP sensor tests normal, replace the ECM.

Component Test

Important: Perform the Circuit/System Test before proceeding with the Component Test.

Dynamic Test

1. Ignition OFF, install a 3-amp 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 0.40-4.55 volts without any spikes or dropouts.

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.