P2127

P2127-ACCELERATOR PEDAL POSITION SENSOR 2 CIRCUIT LOW





For a complete wiring diagram Refer to Diagrams/Electrical.

Theory of Operation


The throttle pedal produces two voltage signals proportional to the pedal movement. The voltages are created by electronic circuitry within the pedal assembly. The primary signal varies between 0 and 5 volts and the secondary signal varies between 0 and 2.5 volts. The Engine Control Module uses the two signals to validate throttle pedal position to control engine fueling. The ECM illuminates the MIL lamp immediately after the diagnostic runs and fails. During this time the customer will be in a limp home mode. The ECM will turn off the MIL lamp after the diagnostic runs and passes in 4 consecutive drive cycles.

- When Monitored:
With the ignition on and no other APPS No.2 DTCs present.

- Set Condition:
When the APP Sensor No.2 voltage is too low. Engine will only idle if the Brake pedal is Pressed or has failed. Acceleration rate and Engine output are limited. One trip fault and the code will set within 5 seconds. ETC light is flashing.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview .


Diagnostic Test


1. APP SENSOR BELOW 0.25 OF A VOLT
NOTE: When this DTC is Active the engine speed, torque, and vehicle speed are limited to a Limp in mode.

Ignition on, engine not running.
With a scan tool, read the APP Sensor No.1 voltage.

NOTE: Sensor No. 2 is pulled low by the ECM as part of its system testing. This test happens a couple of times a second. So you can expect to see voltages close to zero occasionally with a normal sensor.

Is the voltage consistently below 0.25 of a volt?

Yes


- Go To 2


No


- Go To 11



2. (F854) 5-VOLT SUPPLY CIRCUIT




Turn the ignition off.
Disconnect the APP Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F854) 5-volt Supply circuit in the APP Sensor harness connector.
Is the voltage between 4.5 and 5.2 volts?

Yes


- Go To 3


No


- Go To 8



3. ACCELERATOR PEDAL POSITION SENSOR




Connect a jumper wire between the (F854) 5-volt Supply circuit and the (K29) APP Sensor 2 Signal circuit in the Sensor harness connector.
With a scan tool, monitor the APP Sensor No.2 voltage.
Is the voltage above 4.5 volts with the jumper wire installed?

Yes


- Replace the APP Sensor Assembly. After installation is complete, use a scan tool and select the ETC RELEARN function to relearn the APPS values.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test


No


- Go To 4
-
NOTE: Remove the jumper wire before continuing.




4. (K29) APP SENSOR 2 SIGNAL CIRCUIT OPEN
Turn the ignition off.
Disconnect the C2 ECM harness connector.
Measure the resistance of the (K29) APP Sensor 2 Signal circuit from the APP Sensor harness connector to the C2 ECM harness connector.
Is the resistance below 5.0 ohms?

Yes


- Go To 5


No


- Repair the open in the (K29) APP Sensor 2 Signal circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test



5. (K29) APP SENSOR 2 SIGNAL CIRCUIT SHORTED TO GROUND




Measure the resistance between ground and the (K29) APP Sensor 2 Signal circuit in the APP Sensor harness connector.
Is the resistance below 100 ohms?

Yes


- Repair the short to ground in the (K29) APP Sensor 2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test


No


- Go To 6



6. (K29) APP SENSOR 2 SIGNAL CIRCUIT SHORTED TO THE (K400) APP SENSOR 2 RETURN CIRCUIT




Measure the resistance between the (K29) APP Sensor 2 Signal circuit and the (K400) Sensor 2 Return circuit in the APP Sensor harness connector.
Is the resistance below 100 ohms?

Yes


- Repair the short between the (K400) APP Sensor 2 Return circuit and the (K29) APP Sensor 2 Signal circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test


No


- Go To 7



7. (K29) APP SENSOR 2 SIGNAL CIRCUIT SHORTED TO THE (K167) APP SENSOR 1 RETURN CIRCUIT




Measure the resistance between the (K29) APP Sensor 2 Signal circuit and the (K167) Sensor 1 Return circuit in the APP Sensor harness connector.
Is the resistance below 100 ohms?

Yes


- Repair the short between the (K167) App Sensor 1 Return circuit and the (K29) APP Sensor 2 Signal circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test


No


- Go To 10



8. (F854) 5-VOLT SUPPLY CIRCUIT OPEN
Turn the ignition off.
Disconnect the C2 ECM harness connector.
Measure the resistance of the (F854) 5-volt Supply circuit from the Sensor harness connector to the C2 ECM harness connector.
Is the resistance below 5.0 ohms?

Yes


- Go To 9


No


- Repair the open in the (F854) 5-volt Supply circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test



9. (F854) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND




Measure the resistance between ground and the (F854) 5-volt Supply circuit in the APP Sensor harness connector.
Is the resistance below 100 ohms?

Yes


- Repair the short to ground in the (F854) 5-volt Supply circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test


No


- Go To 10



10. ECM
NOTE: Before continuing, check the ECM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?

Yes


- Repair as necessary.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test


No


- Replace and program the Engine Control Module.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test



11. APP SENSOR SWEEP
Ignition on, engine not running.
With a scan tool, monitor the APP Sensor No.2 voltage.
Slowly press the Accelerator pedal down.
Does voltage start at approximately 0.22 of a volt and go above 2.31 volts with a smooth transition?

Yes


- Refer to the INTERMITTENT CONDITION Diagnostic Procedure.Intermittent Condition
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No


- Replace the APP Sensor Assembly. After installation is complete, use a scan tool and select the ETC RELEARN function to relearn the APPS values.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test