Diagnostic Instructions

DTC Descriptors

DTC P2120: Accelerator Pedal Position (APP) Sensor 1 Circuit

DTC P2122: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage

DTC P2123: Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage

DTC P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit

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
APP Sensor 1 Signal	P2122	P2138	P2122	P2123	P2120, P2135
APP Sensor 1 5-Volt Reference	P0335, P0651, P2122, P2135	P2138	P2122	P0651, P2123, P2135	P2120, P2135
APP Sensor 1 Low Reference	--	P2138	P2123	--	P2120, P2135
APP Sensor 2 Signal	P2127	P2138	P2127	P2128	P2120, P2135
APP Sensor 2 5-Volt Reference	P0452, P0532, P0641, P2127, P2135	P2138	P2127	P0641, P2128	P2120, P2135
APP Sensor 2 Low Reference	--	P2138	P2128	--	P2120, P2135

Typical Scan Tool Data

APP Sensor 1

Circuit	Short to Ground	Open	Short to Voltage
Parameter Normal Range: APP 1 varies 1.02-4.29 V
APP Sensor 1 Signal	0 V	0 V	4.98 V
APP Sensor 1 5-Volt Reference	0 V	0 V	4.98 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 0.50-2.50 V
APP Sensor 2 Signal	0 V	0 V	4.98 V
APP Sensor 2 5-Volt Reference	0 V	0 V	4.98 V
APP Sensor 2 Low Reference	--	4.98 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 monitor (ECM) uses the APP sensors input to determine the amount of acceleration or deceleration that is desired.

Conditions for Running DTC

P2120, P2122, P2123, P2125, P2127, P2128

P2138

Conditions for Setting DTC

P2120

The ECM detects that the APP sensor 1 voltage is less than 0.33 volt or more than 4.5 volts for less than 1 second.

P2122

The ECM detects that the APP sensor 1 voltage is less than 0.33 volt for less than 1 second.

P2123

The ECM detects that the APP sensor 1 voltage is more than 4.5 volts for less than 1 second.

P2125

The ECM detects that the APP sensor 2 voltage is less than 0.33 volt or more than 4.5 volts for less than 1 second.

P2127

The ECM detects that the APP sensor 2 voltage is less than or equal to 0.33 volt for less than 1 second.

P2128

The ECM detects that the APP sensor 2 voltage is more than 4.5 volts for less than 1 second.

P2138

The voltage difference between APP sensor 1 and APP sensor 2 exceeds a value of 5 percent with the pedal in the released position, or 10 percent with the pedal at wide open throttle (WOT) for less than 1 second.

Action Taken When the DTC Sets

Conditions for Clearing the MIL/DTC

DTCs P2120, P2122, P2123, P2125, P2127, P2128, and P2138 are Type A DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Description and Operation

Throttle Actuator Control (TAC) System Description

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Circuit/System Verification

1. Ignition ON, observe the scan tool APP sensor 1 voltage parameter. The reading should be between 0.32-4.75 volts, and change with accelerator pedal input.
2. Ignition ON, observe the scan tool APP sensors 2 voltage parameter. The reading should be between 0.32-4.75 volts and change with accelerator pedal input.
3. Ignition ON, observe the scan tool APP sensors 1 and 2 parameter. The scan tool should indicate agree.
4. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.
5. Verify that DTC P2120 or P2125 are not the only throttle position DTCs set.

⇒	If DTC P2120 or P2125 are the only DTCs set, replace the ECM.

6. Verify that DTCs P0641 or P0651 are not set.

⇒	If DTC P0641 or P0651 is set, refer to DTC P0641 or P0651 .

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the accelerator pedal. Allow at least 60 seconds for the ECM to power down. This can be verified by a loss of communication message on the scan tool.
2. Test for less than 5 ohms of resistance between each low reference circuit terminals A and D and ground.

⇒	If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.8 volts between each 5-volt reference circuit terminals C and F and ground.

⇒	If less than 4.8 volts, test the affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.

⇒	If greater than 5.2 volts, test the affected 5-volt reference circuit for short to voltage. If the circuit test normal, replace the ECM.

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

⇒	If greater than 0.1 volt, test the APP sensor 1 and 2 signal circuits terminals B and E for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal F of the APP sensor 1. Verify the scan tool parameter APP sensor 1 voltage is greater than 4.8 volts.

⇒	If less than 4.8 volts, test the APP sensor 1 signal circuit for an open or short to ground. If the circuit tests normal, replace the ECM.

6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C of the APP sensor 2. Verify that the scan tool parameter APP sensor 2 voltage is greater than 4.8 volts.

⇒	If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.

7. Ignition OFF, disconnect the harness connector at the ECM.
8. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:

•	ECM C1 signal circuit terminal 47 to APP terminal E

•	ECM C1 signal circuit terminal 49 to APP terminal B

•	ECM C1 5-volt reference circuit terminal 35 to APP terminal C

•	ECM C1 5-volt reference circuit terminal 33 to APP terminal F

⇒	If greater than 5 ohms, repair the affected circuit for an open/high resistance.

9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.

⇒	If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.

10. If all circuits test normal, test the APP sensor. Refer to Component Testing for instructions.

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

Component Test

Important: The Circuit/System Testing must be performed before proceeding with the Component Test.

Dynamic Test

1. Install a 3A fused jumper wire between the 5-volt reference terminal of the applicable APP sensor and 5 volts. Install a jumper wire between the low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the signal terminal and the low reference terminal with a DMM. The voltage should vary between 0.30-4.98 volts without any spikes or dropouts.

⇒	If the voltage is 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.