GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2006 🢒 Grand Am 🢒 DTC 🢒 DTC P0122

Circuit Description

The throttle position (TP) sensor is used by the powertrain control module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits:

    • A 5-volt reference circuit
    • A low reference circuit
    • A TP sensor signal circuit

The PCM provides the TP sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the wide open throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to more than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively low signal voltage, DTC P0122 sets.

DTC Descriptors

This diagnostic procedure supports the following DTC:

DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The PCM detects that the TP sensor voltage is less than 0.10 volt for more than 25 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.

Test Description

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

  1. The measurement noted in this step will be used in subsequent steps if the measurement is not less than the specified value.

    2.

  2. This step calculates the resistance in the 5-volt reference circuit.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the TP sensor parameter with a scan tool.

Is the voltage less than the specified value?

0.10 V

Go to Step 4

Go to Step 3

3
  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?

--

Go to Step 4

Go to Intermittent Conditions

4
  1. Turn OFF the ignition.
  2. Remove the air cleaner outlet resonator. Refer to Air Cleaner Outlet Resonator Replacement.
  3. Test for shorted terminals and for a poor connection at the throttle position (TP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the TP sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the TP sensor to a good ground with a DMM at the TP sensor connector. Note the measurement as "Supply voltage".

Is the voltage greater than the specified value?

4.8 V

Go to Step 8

Go to Step 6

6
  1. Leave the DMM connected.
  2. Disconnect the air conditioning (A/C) refrigerant pressure sensor and the fuel tank pressure (FTP) sensor, one at a time.
  3. Observe the DMM each time a sensor is disconnected.

Is the voltage greater than the specified value after either of the sensors are disconnected?

4.8 V

Go to Step 15

Go to Step 7

7
  1. Disconnect the DMM from the TP sensor connector.
  2. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor to a good ground, with the DMM, at the A/C pressure sensor connector.

Is the voltage greater than the specified value?

4.8 V

Go to Step 10

Go to Step 13

8

  1. Connect a test lamp and a DMM in series between the 5-volt reference circuit and the low reference circuit of the TP sensor at the harness connector.
  2. Measure the amperage with the DMM. Note the measurement as "Amperage".
  3. Remove the DMM from the circuit.
  4. Connect the test lamp between the 5-volt reference circuit and the low reference circuit of the TP sensor at the harness connector.
  5. Measure the voltage from the 5-volt reference circuit at the test lamp to a good ground with the DMM. Note the measurement as "Load voltage drop".

    6. Important: Before any calculations are performed, ensure that all measurements are converted to like units. For example, volts/amps or millivolts/milliamps.

  6. Subtract the Load voltage drop from the Supply voltage. Note the result as "Supply voltage drop".
  7. Divide the Supply voltage drop by the Amperage.

Is the result greater than the specified value?

5 ohms

Go to Step 11

Go to Step 9

9
  1. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the TP sensor and the signal circuit of the TP sensor.
  2. Observe the TP sensor parameter with a scan tool

Is the voltage more than the specified value?

4.9 V

Go to Step 16

Go to Step 12

10

Test the 5-volt reference circuit between the powertrain control module (PCM) and the TP sensor for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

11

Test the 5-volt reference circuit between the PCM and the TP sensor for high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

12

Test the TP sensor signal circuit between the PCM and the TP sensor for an open or short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

13

Test the 5-volt reference circuits of the following sensors for a short to ground:

    • The TP sensor
    • The A/C refrigerant pressure sensor
    • The FTP sensor

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

14

Test for shorted terminals and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

15

Replace the component for which the voltage changed. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation, and Air Conditioning or Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 18

--

16

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

Did you complete the replacement?

--

Go to Step 18

--

17

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 18

--

18
  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 19

19

Observe the Capture Info with a scan tool.

Have any DTCs not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK