GM Service Manual Online
For 1990-2009 cars only

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 the following 3 circuits:

    • A 5-volt reference
    • A low reference
    • A signal

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 high signal voltage, DTC P0123 sets.

DTC Descriptors

This diagnostic procedure supports the following DTC:

DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage

Conditions for Running the DTC

    • DTC P0107 or P0108 is not set.
    • The engine is running.

Conditions for Setting the DTC

    • The TP sensor signal voltage is more than 4.8 volts.
        OR
    • The TP sensor signal voltage is more than 3.9 volts when the engine speed is less than 1,500 RPM and the MAP is less than 60 kPa.
    • The above conditions are present for longer than 14 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.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls 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. Start the engine.
  2. Allow the engine to idle.
  3. Observe the TP sensor voltage parameter with a scan tool.

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

3.9 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. 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.

Does 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 an intermittent 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 14

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. Observe the TP sensor voltage parameter with a scan tool.

Does the scan tool indicate that the TP voltage is less than the specified value?

0.2 V

Go to Step 6

Go to Step 9

6

Measure the voltage from the 5-volt reference circuit of the TP sensor to a good ground with a DMM.

Is the voltage measurement greater than the specified value?

5.2 V

Go to Step 10

Go to Step 7

7

  1. Connect a jumper wire between each of the terminals in the TP sensor harness connector and the corresponding terminal at the TP sensor. Refer to Using Connector Test Adapters in Wiring Systems.
  2. Measure the voltage from the low reference circuit of the TP sensor at the jumper wire terminal to a good ground with a DMM. Refer to Measuring Voltage Drop in Wiring Systems.

Is the voltage greater than the specified value?

0.2 V

Go to Step 8

Go to Step 12

8

Test the low reference circuit of the TP sensor for a high resistance or an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

9

Test the signal circuit of the TP sensor for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

10

Test all of the 5-volt reference circuits that are shared with the TP sensor for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

11

Test for an intermittent and for a poor connection at the powertrain control module (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 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. 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 15

15

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