GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Tracker - 4WD 🢒 DTC 🢒 DTC P0123

Circuit Description

The DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage diagnostic monitors the TP sensor signal. The TP sensor is a potentiometer whose resistance value changes along with the throttle valve position. The powertrain control module (PCM) provides a 5-volt reference voltage to the TP sensor. The PCM reads the voltage across the TP sensor and uses the voltage to calculate the percentage of throttle valve opening. The TP sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored by the PCM increases. The TP sensor resistance increases when the throttle valve opening decreases, therefore the voltage being monitored by the PCM will decrease.

Throttle Opening

TP Resistance

TP Percentage

TP Signal Voltage

Large

High

High

High

Small

Low

Low

Low

Conditions for Running the DTC

The ignition is ON or the engine is running.

Conditions for Setting the DTC
    • A high TP sensor voltage is indicated at the PCM.
    • The above condition is present for at least 5 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.
    • The PCM enters the Fail-safe mode and assumes the engine throttle valve angle is 24.5 degrees (M/T) or 0 degrees (4 speed A/T).

Conditions for Clearing the MIL/DTC
    • The MIL turns off after 3 consecutively passing cycles without a fault present.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Perform the scan tool clear DTC Information function in order to clear the DTC.

Test Description

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

  1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. If a DTC P2027 is also set there is a fault in the sensor ground circuit or the PCM.

    3.

  3. A typical TP sensor reading on the scan tool will be near 0.73 volts with a 0 percent throttle angle.

    4.

  4. A typical TP sensor reading on the scan tool will be near 0.73 volts with a 0 percent throttle angle.

    5.

  5. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0123 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0123 appears in the Not Ran Since Code Cleared list, the P0123 diagnostic has not yet run. When DTC P0123 does not appear in the Not Ran Since Code Cleared list, the P0123 diagnostic has run. If the MIL is NOT illuminated and there is no Pending DTC Status in DTC Information, the P0123 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.

Step

Action

Value(s)

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

Is a DTC P2027 set?

--

Go to Step 8

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Ensure that the throttle valve is closed.
  3. Select the TP sensor parameter on the scan tool.

Is the TP sensor percentage at the specified value?

99%

Go to Step 5

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Remove the DOME fuse for 30 seconds.
  3. Install the DOME fuse.
  4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
  5. Start the engine.
  6. Operate the vehicle within the Freeze Frame conditions that set the DTC or until the P0123 diagnostic test has run. Refer to the test description.

Does the DTC run and pass?

--

Go to Intermittent Conditions

Go to Step 5

5
  1. Test the TP sensor ground circuit from S106 to the sensor for the following conditions:
    2. • An open circuit
    • High resistance
    • A poor electrical connection at the sensor--Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
  2. Repair as necessary. Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 12

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Ensure that the throttle valve is closed.
  3. Backprobe the TP sensor input circuit at the PCM with a DMM connected to ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Measure the voltage with the DMM set to the DC scale.

Is the voltage within the specified range?

0.50-1.00 V

Go to Step 10

Go to Step 7

7
  1. Test the TP sensor input circuit for a short to voltage.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 12

Go to Step 11

8
  1. Test for an open or high resistance in the TP sensor ground circuit from S106 to the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
  2. Repair as necessary. Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 12

Go to Step 9

9
  1. Inspect the PCM electrical connectors for faulty terminal contact. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair as necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

10

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

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

Did you complete the replacement?

--

Go to Step 12

--

12

  1. Turn OFF the ignition.
  2. Remove the DOME fuse for 30 seconds.
  3. Install the DOME fuse.
  4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
  5. Start the engine.
  6. Operate the vehicle within the Freeze Frame conditions that set the DTC or until the P0123 diagnostic test has run. Refer to the test description.

Does the DTC run and pass?

--

Go to Step 13

Go to Step 2

13

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK