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P2138






P2138-ACCELERATOR PEDAL POSITION SENSOR 1/2 CORRELATION





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 located within the pedal assembly. Each sensor has a 5-Volt reference circuit, a low reference circuit and a signal circuit. Processors are also used to monitor the ETC system data. The processors are located within the Powertrain Control Module (PCM). Each signal circuit provides processors with a signal voltage proportional to pedal movement. The processors share and monitor data to verify that the indicated APP calculation is correct.

- When Monitored:
With the ignition on and no APPS No.1 and APPS No.2 DTC present.

- Set Condition:
APPS values No.1 and No.2 are not coherent. Idle is additionally forced when the brake pedal is pressed or failed. 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.

1. ACTIVE DIAGNOSTIC TROUBLE CODE (DTC)
1. Start the engine and allow it to reach normal operating temperature.

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: Diagnose and repair any system voltage or sensor supply voltage DTCs before continuing with this test.

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. Using the scan tool, read the active DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

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

2. EXCESSIVE RESISTANCE IN THE (K23) APPS NO.1 SIGNAL CIRCUIT




1. Turn the ignition off.
2. Using a Voltmeter perform a voltage drop test. Backprobe the (K23) APPS No.1 Signal circuit at the APPS harness connector and the PCM C1 harness connector. Make sure the Voltmeter leads are connected so a positive polarity is displayed on the Voltmeter.

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 may result in possible serious or fatal injury.

3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the Voltmeter.

Is the voltage below 0.5 Volt?

Yes

- Go To 3

No

- Repair the excessive resistance in the (K23) APP Sensor No.1 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

3. EXCESSIVE RESISTANCE IN THE (K167) APP SENSOR NO.1 GROUND CIRCUIT




1. Turn the ignition off.
2. Move the Voltmeter leads to backprobe the (K167) APP Sensor No.1 Ground circuit at the APPS harness connector and the PCM C1 harness connector. Make sure the Voltmeter leads are connected so a positive polarity is displayed on the Voltmeter.
3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the Voltmeter.

Is the voltage below 0.5 Volt?

Yes

- Go To 4

No

- Repair the excessive resistance in the (K167) APP Sensor No.1 Ground circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

4. EXCESSIVE RESISTANCE IN THE (K29) APP SENSOR NO.2 SIGNAL CIRCUIT




1. Turn the ignition off.
2. Move the Voltmeter leads to backprobe the (K29) APP Sensor No.2 Signal circuit at the APPS harness connector and the PCM C1 harness connector. Make sure the Voltmeter leads are connected so a positive polarity is displayed on the Voltmeter.
3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the Voltmeter.

Is the voltage below 0.5 Volt?

Yes

- Go To 5

No

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

5. EXCESSIVE RESISTANCE IN THE (K400) APP SENSOR NO.2 GROUND CIRCUIT




1. Turn the ignition off.
2. Move the Voltmeter leads to backprobe the (K400) APP Sensor No.2 Ground circuit at the APPS harness connector and the PCM C1 harness connector. Make sure the Voltmeter leads are connected so a positive polarity is displayed on the Voltmeter.
3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the Voltmeter.

Is the voltage below 0.5 Volt?

Yes

- Go To 6

No

- Repair the excessive resistance in the (K400) APP Sensor No.2 Ground circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

6. EXCESSIVE RESISTANCE IN THE (K852) 5-VOLT SUPPLY CIRCUIT




1. Turn the Ignition off.
2. Using a Voltmeter perform a voltage drop test. Backprobe the (K852) 5-Volt Supply circuit at the APPS harness connector and the PCM C1 harness connector. Make sure the Voltmeter leads are connected so a positive polarity is displayed on the Voltmeter.
3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the Voltmeter.

Is the voltage below 0.5 Volt?

Yes

- Go To 7

No

- Repair the excessive resistance in the (K852) 5-Volt Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

7. EXCESSIVE RESISTANCE IN THE (K854) 5-VOLT SUPPLY CIRCUIT




1. Turn the Ignition off.
2. Using a Voltmeter perform a voltage drop test. Backprobe the (K854) 5-Volt Supply circuit at the APPS harness connector and the PCM C1 harness connector. Make sure the Voltmeter leads are connected so a positive polarity is displayed on the Voltmeter.
3. Start the engine and allow it to reach normal operating temperature.
4. Monitor the Voltmeter.

Is the voltage below 0.5 of a Volt?

Yes

- Go To 8

No

- Repair the excessive resistance in the (K854) 5-Volt Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

8. CHECKING APPS NO.1 AND NO.2 WITH A LAB SCOPE
1. Ignition on, engine not running.
2. Set up a lab scope in a way that you can view two graphs simultaneously.
3. Backprobe (K23) APP Sensor No.1 Signal circuit using Channel 1 at the APP Sensor harness connector.
4. Backprobe (K29) APP Sensor No.2 Signal circuit using Channel 2 at the APP Sensor harness connector.

NOTE: 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.

5. Slowly press and release the Accelerator Pedal while monitoring the lab scope screen.

Does the scope pattern show any missing or erratic signals?

Yes

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

No

- Go To 9

9. 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 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. Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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