GM Service Manual Online
For 1990-2009 cars only

Circuit 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 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 more than 2 volts with the accelerator pedal fully depressed.

If the ECM detects that the APP sensor 2 signal voltage is too high, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2138 Accelerator Pedal Position (APP) Sensor 1-2 Correlation

Conditions for Running the DTC

    • The battery voltage is more than 10 volts.
    • The ignition is ON.
    • The accelerator pedal is not in the rest position.
    • DTC P2138 run continuously once the above conditions are met for more than 1 second.

Conditions for Setting the DTC

    • The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 0.25 volt.
    • The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 0.29 volt with a partially pressed pedal.
    • The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 1.09 volts with a fully pressed pedal.
    • The ECM detects that the APP sensor 1 voltage is more then 1.23 when leaving the idle range and the voltage difference between APP sensor 1 and 2 is more than 0.04.
    • Any of the above conditions exist for less than 4 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Observe the DTC information with a scan tool.

Is DTC P0101, P0121, P0122, P0123, P0221, P0222, P0223, P2122, P2123, P2127, P2128 also set?

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Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor electrical connector.
  3. Disconnect the engine control module (ECM).
  4. Measure the resistance of the following circuits with a DMM for each of the APP sensors:
  5. • The low reference circuit
    • The signal circuit
    • The 5-volt reference circuit

Is the resistance more than the specified value for any circuit?

5 ohms

Go to Step 7

Go to Step 4

4

Test the signal circuit of APP sensor 1 for a short to the signal circuit of APP sensor 2. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 7

Go to Step 5

5

Test for an intermittent and for a poor connection at the APP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

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Go to Step 9

Go to Step 6

6

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

7

Repair the high resistance in the circuit that measured above the specified value. Refer to Wiring Repairs .

Did you complete the repair?

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Go to Step 9

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8

Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement .

Did you compete the replacement?

--

Go to Step 9

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9

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 10

10

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

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Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK