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	Signal Performance
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference Circuit	P2122	P2122, P2138	P2122	P2123, P2138	P2138
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit	P0122, P0222, P2122	P2127, P2138	P2127	P0123, P0221, P2128, P2138	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	--	P2138	P2123	--	--
Accelerator Pedal Position (APP) Sensor 1 Low Reference	--	P2138	P2128	--	--

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 volt at rest to above 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 greater than 2 volts with the accelerator pedal fully depressed.

Conditions for Running the DTCs

Conditions for Setting the DTC

P2122

The APP sensor 1 voltage is less than 0.86 volt for greater than 200 milliseconds.

P2123

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

P2127

The APP sensor 2 voltage is less than 0.66 volt for greater than 200 milliseconds.

P2128

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

P2138

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 output of the 5-volt reference circuits if you suspect high resistance in the circuit. The current output 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

Component Connector End Views

Description and Operation

Throttle Actuator Control (TAC) 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 voltage parameters. Verify both of the APP sensor voltages are between 0.4-4.5 volts.
2. 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.
3. 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.
4. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. 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, disconnect the harness connector at the accelerator pedal assembly.
2. Remove the fuse that supplies B+ to terminal X2-56 of the ECM.
3. Test for less than 5 ohms between the appropriate low reference circuit listed below and ground.

•	APP Sensor 1 Terminal 4

•	APP Sensor 2 Terminal 3

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

4. Install the fuse that supplies B+ to terminal X2-56 of the ECM.

Important: The 5-volt reference circuits are internally and externally connected at the ECM. Other component DTCs may be set. If other DTCs are set, review the electrical schematic and diagnose the applicable circuits and components.

5. Ignition ON, test for 4.8-5.2 volts between the appropriate 5-volt reference circuit listed below and ground.

•	APP Sensor 1 Terminal 6

•	APP Sensor 2 Terminal 1

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

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

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

⇒	If greater than the specified range, test the signal circuit of the for a short to voltage. If the circuit tests normal, replace the ECM.

7. Install a 3A fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit listed below. Verify the APP sensor voltage parameter is greater than 4.8 volts.

•	APP Sensor 1 Terminals 6 and 5

•	APP Sensor 2 Terminals 1 and 2

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

⇒	If both APP sensor voltage parameters display greater than the specified range, test the signal circuits of the APP sensors for a shorted together condition. If the circuits test normal, replace the ECM.

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

Component Testing

1. Install a 3A fused jumper wire between the applicable APP 5-volt reference terminal and 5 volts.
2. Install a jumper wire between the applicable APP low reference terminal and ground.
3. 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.