Diagnostic Instructions

DTC Descriptors

DTC P2121: Accelerator Pedal Position (APP) Sensor 1 Performance

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

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	P0106, P0405, P2122, P2138	P2121, P2138	P2122, P2138	P2123	--
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference Circuit	P0122, P0222, P2122, P0532, P2119, P2127, P2135, P2138	P0121, P0221, P2121, P2138	P2127, P2138	P0123, P0223, P2123	--
Accelerator Pedal Position (APP) Sensor 1 Signal	P2122, P2138	P2121, P2138	P2122, P2138	P2123	P2121
Accelerator Pedal Position (APP) Sensor 2 Signal	P2127, P2138	P2121, P2138	P2127, P2138	P2128	P2121
Accelerator Pedal Position (APP) Sensor 1 Low Reference	--	P2121, P2138	P2123, P2138	--	--
Accelerator Pedal Position (APP) Sensor 2 Low Reference	--	--	P2128, P2138	--	--

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 1 Volts Parameter Normal Range: APP Sensor 2 0.5 Volts
5-Volt Reference	0.00 Volts	0.00 Volts	5.00 Volts
APP Sensor 1 Signal	0.00 Volts	0.04 Volts	5.00 Volts
APP Sensor 2 Signal	0.00 Volts	0.10 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 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 1.0 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

P2121

P2122

The APP sensor 1 voltage is less than 0.89 volt for greater than 4 seconds.

P2123

The APP sensor 1 voltage is greater than 4.82 volts for greater than 4 seconds.

P2127

The APP sensor 2 voltage is less than 0.82 volt for greater than 4 seconds.

P2128

The APP sensor 2 voltage is greater than 4.82 volts for greater than 4 seconds.

Action Taken When the DTC Sets

DTCs P2121, P2122, P2123, P2127, and P2128 are Type A DTCs.

Conditions for Clearing the DTC

DTCs P2121, P2122, P2123, P2127, and P2128 are Type A DTCs.

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 scan tool APP Sensor parameters. Both readings should be 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 P2121, P2122, P2123, P2127, or P2128 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 P2121, P2122, P2123, P2127, or P2128 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 you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the accelerator pedal assembly.
2. Test for less than 5 ohms of resistance between the appropriate low reference circuit and ground.

•	APP sensor 1 low reference circuit terminal 4

•	APP sensor 2 low reference circuit 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 circuits test 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. Install the MAIN fuse. 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 6

•	APP sensor 2 5-volt reference circuit terminal 1

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

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

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

⇒	If greater than the specified range, test the appropriate signal circuit for a short to voltage. If the circuits test 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 parameter is greater than 4.8 volts.

•	APP sensor 1 signal circuit terminal 5

•	APP sensor 2 signal circuit terminal 2

•	APP sensor 1 5-volt reference circuit terminal 6

•	APP sensor 2 5-volt reference circuit terminal 1

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

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

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.