GM Service Manual Online
For 1990-2009 cars only

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 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.

Conditions for Setting The DTC

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

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC

    • 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 non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

The scan tool reads throttle position in volts. The TP should read between 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 the wide open throttle (WOT) position.

Also, some scan tools will read the throttle angle: 0 percent equals closed throttle and 100 percent equals 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 a 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) with the throttle closed, to more than 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 inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.

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

Test Description

The number below refers to the step number on 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

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. Verify the throttle is closed.
  2. Install the scan tool.
  3. Turn ON the ignition, with 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

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 PCM 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 PCM and TP sensor harness connectors.
  2. Turn ON the ignition, with 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 and 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 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 8

Go to Step 2

8

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the applicable DTC table

System OK