GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0122

Circuit Description

The throttle position (TP) sensor is used by the PCM in order to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit. The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the wide open throttle (WOT) provides the PCM with a signal voltage less than 1 volt to more than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively low voltage, the DTC will set.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC
    • The TP sensor signal voltage is less than 0.2 volt.
    • The above conditions are present for 10 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 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

The PCM 5-volt reference circuits are internally connected within the PCM. If all the TP sensor circuits are OK, inspect the MAP sensor, and inspect the exhaust gas recirculation (EGR) valve for malfunctions.

If the DTC occurs intermittently, performing the DTC P1122 diagnostic test may isolate the cause of the fault. Refer to DTC P1122 .

For an intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. If DTC P1639 sets at the same time, the 5-volt reference circuit is either shorted to ground or shorted to a voltage. The 5-volt reference circuit is internally connected within the PCM.

    2.

  2. This step verifies that a malfunction is present.

    3.

  3. Using Freeze Frame/Failure Records data may help to locate an intermittent condition. If you cannot duplicate the DTC, the information in the Freeze Frame/Failure Records data can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also help to determine how many ignition cycles have occurred since the diagnostic reported a pass and/or a fail. In order to isolate when the DTC failed, operate vehicle within the same Freeze Frame conditions that you observed. These conditions include the RPM, the vehicle load, the vehicle speed, and the temperature.

    4.

  4. This determines if the short is caused from the Accelerator and Servo Control Module (ASM).

    5.

  5. If the scan tool indicates 5 volts, the TP sensor circuits and the PCM are OK.

    6.

  6. Disconnecting the PCM will allow using the DMM in order to test the circuit continuity. This will help to locate an open or shorted circuit.

    7.

  7. Disconnecting the PCM will allow using the DMM in order to test the circuit continuity. This will help to locate an open or shorted circuit.

Step

Action

Values

Yes

No

Schematic Reference : Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Install the scan tool.
  2. Idle the engine.
  3. Monitor the Diagnostic Trouble Code (DTC) Information using the scan tool.

Did DTC P1635 or P1639 set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. With the throttle closed, monitor the TP sensor display on the scan tool.

Does the scan tool indicate TP voltage below the specified value?

0.2 V

Go to Step 5

Go to Step 4

4

  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame/Failure Records data for this DTC and record the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Start the engine.
  5. Operate the vehicle within the conditions required for this diagnostic to run. Attempt to duplicate the conditions recorded in the Freeze Frame/Failure Records. Special operating conditions that you must meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
  6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number which was set using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 5

Go to Diagnostic Aids

5

Important: 

   • If this vehicle does not have traction control, go to Step 6.
   • After you complete this step, reconnect the Accelerator and Servo Control Module (ASM). Also, clear any ASM DTCs that may have set when the ASM was disconnected.

  1. Turn OFF the ignition.
  2. Disconnect the ASM. Refer to Accelerator and Servo Control Module Replacement in Antilock Brake Systems.
  3. Turn ON the ignition.

Does the scan tool indicate that the TP sensor voltage is still below the specified value?

0.2 V

Go to Step 6

Go to Diagnostic System Check - ABS in Antilock Brake System

6

  1. Disconnect the TP sensor electrical connector.
  2. Jumper the 5-volt reference circuit and the TP signal circuit together at the TP sensor harness connector.
  3. Observe the TP sensor voltage display on the scan tool.

Does the scan tool indicate that the TP sensor voltage is still below the specified value?

4.7 V

Go to Step 7

Go to Step 12

7
  1. Connect the test lamp J 35616-200 between B+ and the TP sensor signal circuit at the TP sensor harness connector.
  2. Observe the TP sensor voltage display on the scan tool.

Does the scan tool indicate that the TP sensor voltage is above the specified value?

4.7 V

Go to Step 8

Go to Step 10

8

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C1. Refer to Powertrain Control Module Replacement .
  3. Test the 5-volt reference circuit for an open or short to ground.
  4. If the 5-volt reference circuit is open or shorted to ground, repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 9

9
  1. Test the 5-volt reference circuit for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a poor connection, repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

10

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2.
  3. Test the signal circuit for an open, a short to ground, or a short to the sensor ground circuit.
  4. If you find the sensor signal circuit is open or shorted to ground, repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

11
  1. Test the sensor signal circuit for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a poor connection, repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

12

Replace the TP sensor. Refer to Throttle Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

13

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 14

--

14
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 15

Go to Step 2

15

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK