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P2127






P2127-ACCELERATOR PEDAL POSITION SENSOR 2 CIRCUIT LOW

For a complete wiring diagram, refer to the Wiring Information.





Theory of Operation

The Electronic Throttle Control (ETC) system uses two Accelerator Pedal Position (APP) Sensors to monitor the accelerator pedal position. The APP Sensors 1 and 2 are integrated into one assembly located at the pedal assembly. Each sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The Powertrain Control Module (PCM) reads the two signals individually and then compares the two signals as a redundant check of the throttle position. One of the sensors will fluctuate between 0 volts and 5.0 volts and the other sensor will fluctuate between 0 volts and 2.5 volts. The fluctuation of the two sensors should move proportionately. E.G. When operating properly, the voltage reading of the sensor operating on the 5.0 volt scale will always approximately two time the voltage reading of the sensor on the 2.5 volts scale.

- When Monitored:
With the ignition on.

- Set Condition:
When the APP Sensor No.2 voltage is below 0.3 volts for 0.5 seconds. Acceleration rate and Engine output are limited. One trip fault and the code will set within five seconds. ETC light is flashing.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

Diagnostic Test

1. ACTIVE DTC

NOTE: When this DTC is Active the engine speed, torque and vehicle speed are limited to a Limp in mode.

NOTE: If there are any 5-Volt Reference DTCs present, diagnose and repair those DTCs before continuing with this test procedure.

1. Turn the ignition on.

WARNING:
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in possible serious or fatal injury.

NOTE: If you are viewing data recorder information or Freeze Frame data the APP Sensor No. 2 is pulled low by the PCM as part of its system testing. This test happens every 320 milliseconds and may not show up on the scan tool but may show up on a data recorder or lab scope. It is acceptable to see the voltage close to zero with a normal sensor when using a data recorder/lab scope.

2. With the scan tool, select View DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Go To 9

2. CHECK THE (K854) 5-VOLT SUPPLY CIRCUIT VOLTAGE
1. Turn the ignition off.
2. Disconnect the APP Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage on the (K854) 5-Volt Supply circuit in the APP Sensor harness connector.

Is the voltage between 4.8 and 5.2 volts?

Yes

- Go To 3

No

- Repair the (K854) 5-Volt Supply circuit for an open circuit or short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

3. CHECK THE (K29) APP SENSOR NO.2 SIGNAL CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the PCM C1 harness connectors.
3. Measure the resistance of the (K29) APP Sensor No.2 Signal circuit between the APP Sensor harness connector and the PCM C1 harness connectors.

Is the resistance below 5.0 Ohms?

Yes

- Go To 4

No

- Repair the open in the APP Sensor No.2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

4. CHECK THE (K29) APP SENSOR NO.2 SIGNAL CIRCUIT FOR A SHORT TO GROUND
1. Measure the resistance between ground and the (K29) APP Sensor No.2 Signal circuit in the APP Sensor harness connector.

Is the resistance above 10k Ohms?

Yes

- Go To 5

No

- Repair the short to ground in the (K29) APP Sensor No.2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

5. CHECK FOR THE (K29) APP SENSOR NO.2 SIGNAL CIRCUIT SHORTED TO THE (K400) APP SENSOR NO.2 RETURN CIRCUIT
1. Measure the resistance between the (K29) APP Sensor No.2 Signal circuit and the (K400) APP Sensor No.2 Return circuit in the APP Sensor harness connector.

Is the resistance above 10k Ohms?

Yes

- Go To 6

No

- Repair the short between the (K29) APP Sensor No.2 Return circuit and the (K400) APP Sensor No.2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

6. CHECK FOR THE (K29) APP SENSOR NO.2 SIGNAL CIRCUIT SHORTED TO THE (K167) APP SENSOR NO.1 RETURN CIRCUIT
1. Measure the resistance between the (K29) APP Sensor No.2 Signal circuit and the Sensor No.1 Return circuit in the (K167) APP Sensor harness connector.

Is the resistance above 10k Ohms?

Yes

- Repair the short between the (K29) APP Sensor No.1 Return circuit and the (K167) APP Sensor No.2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 7

7. ACCELERATOR PEDAL POSITION SENSOR
1. Reconnect the PCM harness connectors.
2. Turn the ignition on.
3. With the scan tool, monitor the APP Sensor No.2 voltage.
4. Connect a jumper between the (K854) 5-Volt Supply circuit and the (K29) APP Sensor No.2 Signal circuit in the Sensor harness connector.

NOTE: The sensor voltage should be approximately 5.0 volts (plus or minus.1 volts) with the jumper in place.

Does the scan tool display the voltage as described above?

Yes

- Verify that there is good pin to terminal contact in the APP Sensor and Powertrain Control Module connectors. If OK, replace the APP Sensor Assembly. Removal. After installation is complete, use a scan tool and perform the Reset Accelerator Pedal Adaptives to relearn the APPS values.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 8

NOTE: Remove the jumper before continuing.

8. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Accelerator Pedal Position Sensor and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the APP Sensor and Powertrain Control Module harness connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

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

No

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

9. APP SENSOR SWEEP
1. Turn the ignition on.
2. With the scan tool, monitor the APP Sensor No.2 voltage.
3. Slowly press the Accelerator pedal down.

Does voltage start at approximately 0.22 volts and go to approximately 2.31 volts with a smooth transition?

Yes

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

No

- Verify that there is good pin to terminal contact in the APP Sensor and Powertrain Control Module connectors. If OK, replace the APP Sensor Assembly. Removal. After installation is complete, use a scan tool and perform the Reset Accelerator Pedal Adaptives to relearn the APPS values.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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