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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 DTC 🢒 DTC P2138

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 1.0 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 difference between APP sensor 1 and 2 signal voltage is more than a predetermined value, 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 ignition is ON or the engine is running.
    • DTC P2138 run continuously once the above conditions are met.

Conditions for Setting the DTC

This DTC set when one of the following conditions occur:

    • The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 0.21 volt.
    • The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 0.27 volt with a partially pressed pedal.
    • The ECM detects that the voltage difference between APP sensor 1 and 2 is more than 1.07 volts with a fully pressed pedal.
    • The ECM detects that the APP sensor 1 voltage is more then 1.11 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.

Diagnostic Aids
    • Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
    • The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views .
    • If DTCs P0700, P2122, P2128, and P2138 are set together in various combinations, inspect the APP sensor 1 and 2 signal circuits for being shorted together.
    • For an intermittent condition, refer to Intermittent Conditions .

DTC P2138

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
  1. Turn the ignition switch to ON position, with the engine OFF.
  2. Perform the following tests:
    3. • Rapidly depress the accelerator pedal from the rest position to the wide open throttle position (WOT) and release pedal. Repeat the procedure several times.
    • Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle. Repeat the procedure several times.
  3. Observe the APP sensors 1 and 2 parameter with a scan tool.

Does the scan tool display Agree?

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Go to Step 4

Go to Step 3

3

Observe the DTC information with a scan tool.

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

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records for this DTC.
  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?

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Go to Step 5

Go to Diagnostic Aids

5
  1. Turn OFF the ignition.
  2. Disconnect the APP sensor harness connector.
  3. Turn the ignition switch to ON position, with the engine OFF.

    4. Important: Use the J 35616-200 Test Lamp Kit for this test. If the J 35616-200 is not available, use a test lamp that measures more than 20 ohms.

  4. Connect a test lamp between the 5-volt reference circuit of the APP sensor 1 and a good ground.
  5. Connect a DMM to the probe of the test lamp and a good ground. Refer to Measuring Voltage Drop .

Is the voltage within the specified range?

4.8-5.1 V

Go to Step 6

Go to Step 11

6

    Important: Use the J 35616-200 for this test. If the J 35616-200 is not available, use a test lamp that measures more than 20 ohms.

  1. Connect a test lamp between the 5-volt reference circuit of the APP sensor 2 and a good ground.
  2. Connect a DMM to the probe of the test lamp and a good ground. Refer to Measuring Voltage Drop .

Is the voltage within the specified range?

4.8-5.1 V

Go to Step 7

Go to Step 11

7
  1. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the APP sensor 1.
  2. Observe the APP sensor 1 voltage parameter with a scan tool.

Is the voltage more than the specified value?

4.8 V

Go to Step 8

Go to Step 12

8
  1. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the APP sensor 2.
  2. Observe the APP sensor 2 voltage parameter with a scan tool.

Is the voltage more than the specified value?

4.8 V

Go to Step 9

Go to Step 12

9
  1. Turn OFF the ignition.
  2. Remove the ECM/TCM fuse from the underhood fuse block.

    3. Notice: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.

  3. Measure the resistance from the low reference circuit of the APP sensor 1 to the ECM housing with a DMM.

Is the resistance less than the specified value?

5 Ω

Go to Step 10

Go to Step 13

10

Notice: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.

Measure the resistance from the low reference circuit of the APP sensor 2 to a good ground, with a DMM.

Is the resistance less than the specified value?

5 Ω

Go to Step 14

Go to Step 13

11

Important: The 5-volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5-volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5-volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors.

Test the 5-volt reference circuit of the APP sensor 1 or 2 for a high resistance, a short to ground, a short to voltage, or for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

12

Test the signal circuit of the APP sensor 1 or 2 for a high resistance, a short to ground, or for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

13

Test the low reference circuit of the APP sensor 1 or 2 for a high resistance, or for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

14

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 19

Go to Step 15

15

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?

--

Go to Step 19

Go to Step 17

16

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 19

Go to Step 18

17

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

Did you compete the replacement?

--

Go to Step 19

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18

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 19

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19
  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 20

20

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK