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	P0698	P2138	P2122	P0123, P0223, P2123	--
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit	P0698	P2138	P2127	P0108, P2123	--
Accelerator Pedal Position (APP) Sensor 1 Signal	P2122, P2138	P2123, P2138	P2122, P2138	P2123	P2138
Accelerator Pedal Position (APP) Sensor 2 Signal	P2127, P2138	P2138	P2127, P2138	P2128	P2138
Accelerator Pedal Position (APP) Sensor 1 Low Reference	--	P2128, P2138	P2123	--	--
Accelerator Pedal Position (APP) Sensor 1 Low Reference	--	--	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 0.7 Volts Parameter Normal Range: APP Sensor 2 0.3 Volts
5-Volt Reference	0.00 Volts	0.00 Volts	5.00 Volts
APP Sensor 1 Signal	0.00 Volts	0.00 Volts	5.00 Volts
APP Sensor 2 Signal	0.00 Volts	0.00 Volts	5.00 Volts
APP Sensor 1 Low Reference	--	5.00 Volts	--
APP Sensor 2 Low Reference	--	5.00 Volts	--

Circuit/System Description

The accelerator pedal assembly contains 2 accelerator pedal position (APP) sensors. The APP sensors are mounted to the accelerator pedal assembly and are not serviceable. The APP sensors provide a signal voltage that changes relative to pedal position. The engine control module (ECM) supplies each APP sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit.

The APP sensor 1 signal voltage increases as the pedal is depressed, from approximately 0.7 volt at rest to above 4 volts when fully depressed. The APP sensor 2 signal voltage increases as the pedal is depressed, from approximately 0.3 volt at rest to greater than 2 volts with the accelerator pedal fully depressed.

Conditions for Running the DTC

P2122

P2123 or P2128

P2127

P2138

OR

Conditions for Setting the DTC

P2122

The ECM detects that the APP sensor 1 voltage is less than 0.29 volt for less than 3 seconds.

P2123

The ECM detects that the APP sensor 1 voltage is greater than 4.8 volts for less than 3 seconds.

P2127

The ECM detects that the APP sensor 2 voltage is less than 0.17 volt for less than 3 seconds.

P2128

The ECM detects that the APP sensor 2 voltage is greater than 3.9 volts for less than 3 seconds.

P2138

The ECM detects that APP sensor 1 and APP sensor 2 disagree greater than a calibrated amount for greater than 3 seconds.

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

If a shared 5-volt reference circuit is shorted to ground or shorted to a voltage, other 5-volt reference circuits may be affected.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

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 DTC information with a scan tool. Verify that DTC P0642 or P0643 is not set.

⇒	If any of the DTCs are set, refer to DTC P0642 or P0643.

2. Ignition ON, verify both of the scan tool APP sensor voltage parameters are between 0.3-4.5 volts.
3. Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release the pedal. Repeat the procedure several times. DTCs P2122, P2123, P2127, P2128, or P2138 should not set.
4. 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.
5. 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 you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the accelerator pedal assembly.
2. Ignition OFF for at least 20 seconds, test for less than 5 ohms of resistance between the appropriate low reference circuit and ground.

•	APP Sensor 1 low reference terminal 3

•	APP Sensor 2 low reference terminal 5

⇒	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.

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.

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

•	APP Sensor 1 5 volt reference circuit terminal 2

•	APP Sensor 2 5 volt reference circuit 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.

4. 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 for a short to voltage. If the circuit tests normal, replace the ECM.

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

•	APP Sensor 1 signal circuit terminal 4

•	APP Sensor 2 signal circuit terminal 6

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

⇒	If both scan tool APP sensor voltage parameters display greater than 4.8 volts, test the signal circuits of the APP sensors for a shorted together condition. If the circuits test normal, replace the ECM.

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

Component Testing

1. Ignition OFF, disconnect the harness connector at the accelerator pedal assembly.
2. Test for 1160-1175 ohms between the appropriate 5-volt reference terminal and the appropriate low reference terminal.

•	APP Sensor 1 5 volt reference circuit terminal 2

•	APP Sensor 2 5 volt reference circuit terminal 1

•	APP Sensor 1 low reference terminal 3

•	APP Sensor 2 low reference terminal 5

⇒	If not within the specified range, replace the accelerator pedal assembly.

3. Sweep the sensor through the entire range while monitoring the resistance between the appropriate signal terminal and the appropriate low reference terminal. The resistance should vary between 1530 and 630 ohms for APP Sensor 1, and 3060 and 252 ohms for APP Sensor 2 without any spikes or dropouts.

•	APP Sensor 1 signal circuit terminal 4

•	APP Sensor 2 signal circuit terminal 6

•	APP Sensor 1 low reference terminal 3

•	APP Sensor 2 low reference terminal 5

⇒	If not within the specified range or is erratic, replace the accelerator pedal assembly.

4. Sweep the APP sensor through the entire range while applying 5 volts and ground to the applicable terminals. Test the voltage between the appropriate signal and the appropriate low reference terminals. The voltage should vary between 4.3-1.2 volts for APP Sensor 1, and 0.5-2.4 volts for APP Sensor 2 without any spikes or dropouts.

•	APP Sensor 1 signal circuit terminal 4

•	APP Sensor 2 signal circuit terminal 6

•	APP Sensor 1 low reference terminal 3

•	APP Sensor 2 low reference terminal 5

⇒	If not within the specified range or is erratic, replace the accelerator pedal assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.