GM Service Manual Online
For 1990-2009 cars only

Object Number: 426047  Size: LF
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
Emission Controls
OBD II Symbol Description Notice

Circuit Description

The throttle position (TP) sensor is a potentiometer. The control module supplies the TP sensor a reference voltage, a signal, and ground 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 intermittent low signal voltage on the TP sensor signal circuit.

Conditions for Running the DTC

The engine is running.

The Conditions for Setting the DTC

The VCM detects an intermittent low TP sensor voltage while the engine is running.

Action Taken When the DTC Sets

    • The control module stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL).
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

    • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
    • A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
    • Use the scan tool Clear Information function.

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).

Also, some scan tools will read the throttle angle. 0 percent = closed throttle. 100 percent = WOT.

An intermittent open or short to ground in the 5 volt reference circuit or the TP sensor signal circuit could result in a DTC P1122. If the low voltage reading is present, additional sensor circuit voltage codes could be set. Refer to any non-intermittent DTCs that are set.

Observe the TP sensor while depressing the accelerator pedal with the ignition turned ON leaving the engine OFF. The display should vary from about 0.5 volts (500 mV) when throttle was closed, to over 4.5 volts (4500 mV) when throttle is held at the Wide Open Throttle (WOT) position.

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

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

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

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

Test Description

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

  1. If the TP sensor voltage is less than 0.25 volts, then the condition is present. Even though DTC P0122 did not set, this DTC is more comprehensive and may aid in diagnosis.

Step

Action

Value(s)

Yes

No

1

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

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Verify the throttle is closed.
  2. Install the scan tool.
  3. Turn ON the ignition leaving the engine OFF.
  4. Display the TP sensor voltage.

Is the TP sensor voltage less than the specified value?

0.25 V

Go to DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the TP sensor harness connector.
  3. Inspect the TP sensor connector and terminals.

Did you find a problem?

--

Go to Step 6

Go to Step 4

4

  1. Disconnect the VCM C2 and C3 connectors.
  2. Inspect the terminals and connectors.

Did you find a problem?

--

Go to Step 6

Go to Step 5

5

  1. Reconnect the VCM and TP sensor harness connectors.
  2. Turn ON the ignition leaving the engine OFF.
  3. Check for an intermittent open circuit or short to ground in the TP sensor signal circuit or 5 volt reference circuit while moving the harness in various locations.
  4. Display the TP sensor voltage while moving the harness.

Did the voltage decrease?

--

Go to Step 6

Go to Diagnostic Aids

6

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

Is the action complete?

--

Go to Step 7

--

7

  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 which was set.
  6. Operate the vehicle, with 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 8

Go to Step 2

8

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the applicable DTC table

System OK