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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 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, both APP Sensor voltage Signal voltages are above 0.297 volts and no active APPS No.1 or APPS No.2 circuit high or circuit low DTCs present.

- Set Condition:
There are two fail conditions for this fault. Condition one; When APP Sensor No.1 voltage is below 1.78 volts, the input signal difference between APP Sensor No.1 and APP Sensor No.2 is 8.4% of pedal position. Condition two; When APP Sensor No.1 voltage is above 1.78 volts, the input signal difference between APP Sensor No.1 and APP Sensor No.2 is 13.3% of pedal position. 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: If there are any 5-Volt Reference DTCs present, diagnose and repair those DTCs before continuing with this test procedure.

1. Test drive the vehicle.

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. CHECK FOR EXCESSIVE RESISTANCE IN THE (K23) APP SENSOR NO.1 SIGNAL CIRCUIT
1. Turn the ignition off.
2. Disconnect the APP Sensor harness connector.
3. Disconnect the PCM C1 harness connector.
4. Measure the resistance of the (K23) APP Sensor No.1 Signal circuit between the APP Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

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. CHECK FOR EXCESSIVE RESISTANCE IN THE (K167) APP SENSOR NO.1 RETURN CIRCUIT
1. Measure the resistance of the (K167) APP Sensor No.1 Signal Return circuit between the APP Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 4

No

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

4. EXCESSIVE RESISTANCE IN THE (K29) APP SENSOR NO.2 SIGNAL CIRCUIT
1. Measure the resistance of the (K29) APP Sensor No.2 Signal Signal circuit between the APP Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

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 RETURN CIRCUIT
1. Measure the resistance of the (K400) APP Sensor No.2 Signal Return circuit between the APP Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

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. Measure the resistance of the (K852) 5-Volt Supply circuit between the APP Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

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. Measure the resistance of the (K854) 5-Volt Supply circuit between the APP Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

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. CHECK APPS NO.1 AND NO.2 WITH A LAB SCOPE
1. Reconnect the APP Sensor harness connector.
2. Reconnect the PCM C1 harness connector.
3. Using a lab scope, back probe the APP Sensor No.1 Signal circuit using Channel 1 at the APP Sensor harness connector.
4. Back probe the APP Sensor No.2 Signal circuit using Channel 2 at the APP Sensor harness connector.
5. Set up the lab scope in a way that you can view two graphs simultaneously.
6. Turn the ignition on.

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.

7. 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 perform the Reset Accelerator Pedal Adaptives 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. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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