GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2002 🢒 Unit Repair 🢒 DTC 🢒 DTC P0122

Circuit Description

The throttle position (TP) sensor is a potentiometer. The powertrain control module (PCM) supplies the TP sensor a reference voltage, a signal, and low reference circuits. When the throttle is depressed, the TP sensor signal rises to near the reference voltage. When the throttle is released, the TP sensor signal decreases from the reference voltage. The control module monitors the TP sensor signal circuit voltage in order to determine the throttle blade angle, or opening.

This DTC is designed to detect a TP sensor signal voltage lower than the possible operating range of a normally functioning TP sensor.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The TP sensor signal voltage is less than 0.25 volts for 1 second or more.

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 scan tool reads throttle position in volts. The TP should read about 0.45-0.85 volts with the throttle closed and the ignition ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward wide open throttle (WOT).

The scan tool will also read the throttle angle percentage. 0 percent at closed throttle. 100 percent at wide open throttle (WOT).

An open or short to ground in the 5 volt reference circuit or the TP sensor signal circuit results in a DTC P0122. Refer to Symptoms - Engine Controls .

Scan the TP sensor signal while depressing the accelerator pedal with the engine stopped and the ignition ON. The display should vary from below 1.25 volts (1250 mV) with the throttle closed, to more than 4.5 volts (4500 mV) when the throttle is held at the wide open throttle (WOT) position.

An intermittent may be caused by any of the following conditions:

    • A poor connections
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittent and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs in Wiring Systems.

Test Description

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

  1. If the TP signal measures less than 0.25 volt, then the low voltage condition exists.

    2.

  2. If the PCM recognizes the high signal voltage, the PCM and the wiring are okay.

    3.

  3. The 5 volt reference of the PCM supply is shared by the MAP, TP, and EGR position sensors. A short to ground at ANY of the sensors 5 volt reference circuits OR an internally shorted sensor may cause this DTC to set. In order to determine the location of a shorted 5 volt reference supply, disconnect the sensors one at a time beginning with the MAP sensor.

    4.

  4. The sensor connectors must remain disconnected while the PCM connector remains connected for this step. The PCM terminals 12 and 27 are spliced together inside the PCM. When checking the 5 volt reference circuit for a short to ground, both the 5 volt reference circuits must be checked.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Important: Before clearing the DTCs, use the scan tool Capture Info function to save the Freeze Frame/Failure Records for reference. The control modules data is deleted once the Clear Info function is used.

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. Turn ON the ignition, with the engine OFF.
  3. Close the throttle.
  4. Monitor the TP sensor voltage display.

Does the scan tool display a TP sensor voltage less than the specified value?

0.25 V

Go to Step 4

Go to Step 3

3

Depress the accelerator pedal to wide open throttle (WOT) while monitoring the TP angle on the scan tool.

Does the TP angle increase smoothly through the specified range?

0-100%

Go to Step 4

Go to Step 5

4

Is DTC P1635 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 5

5

  1. Disconnect the TP sensor harness connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Jumper the TP sensor 5 volt reference circuit and the TP sensor signal circuit together at the TP sensor harness connector.

Does the scan tool display a TP sensor voltage more than the specified value?

4.0 V

Go to Step 13

Go to Step 6

6
  1. Remove the jumper.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the TP sensor 5 volt reference circuit at the TP sensor harness connector with a DMM connected to a ground.

Is the voltage more than the specified value?

4.7 V

Go to Step 14

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector.
  3. Check the 5-volt reference circuit for an open.

Did you find a problem?

--

Go to Step 19

Go to Step 8

8

  1. Connect the PCM connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the TP sensor 5 volt reference circuit at the TP sensor harness connector with a DMM connected to a ground.
  4. Disconnect the following sensors individually:
    5. • EGR
    • MAP
  5. Monitor the DMM while disconnecting the sensors.

Did the voltage read more than the specified value after disconnecting one of the sensors?

4.7 V

Go to Step 9

Go to Step 12

9

Was the suspect sensor the EGR sensor?

--

Go to Step 10

Go to Step 11

10

Check for a short between the 5 volt reference circuit and the EGR feed control circuit.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 11

11
  1. Replace the sensor that caused the voltage reading to go more than the specified value.
  2. Refer to one of the following: Manifold Absolute Pressure Sensor Replacement , Exhaust Gas Recirculation Valve Replacement , or Fuel Tank Replacement .

Did you complete the replacement?

4.7 V

Go to Step 21

--

12

  1. Ensure that all sensor connectors are still disconnected.
  2. Turn OFF the ignition.
  3. Probe the 5 volt reference circuit at the TP sensor harness connector with a test lamp connected to B+.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 17

13

Check for a poor connection at the TP sensor.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

14

Check the TP sensor signal circuit for a short to ground.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 15

15

Check the TP sensor signal circuit for an open.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 20

16

Repair the short to ground in the 5-volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 21

--

17
  1. Disconnect the PCM C3 connector.
  2. Check for a poor connection.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 20

18

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

Did you complete the replacement?

--

Go to Step 21

--

19

Repair the circuit as necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems

Did you complete the repair?

--

Go to Step 21

--

20
  1. Replace the PCM. Refer to Powertrain Control Module Replacement .
  2. Perform the Passlock Reprogramming Procedure. Refer to PASSLOCK Reprogramming Seed and Key in Theft Deterrent.
  3. Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

Did you complete the replacement?

--

Go to Step 21

--

21
  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches normal operating temperature.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number that was set.
  6. Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 22

Go to Step 2

22

Does the scan tool display any additional undiagnosed DTCs?

--

Go to Diagnostic Trouble Code (DTC) List

System OK