GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage diagnostic detects an out of range 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

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage

Conditions for Running the DTC

    • The ignition is ON or the engine is running.
    • DTC P0123 runs continuously once the above condition has been met.

Conditions for Setting the DTC

The TP sensor input to the PCM is more than 4.9 volts for at least 5 seconds.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM stores the conditions that were present when the DTC set as Freeze Frame data.
    • The TP sensor angle will default to 0 percent.

Conditions for Clearing the MIL/DTC

    • The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run, and the fault condition is no longer present.
    • A DTC clears after 40 consecutive warm-up cycles have occurred without a fault.
    • A DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

On a good TP sensor the scan tool will typically display a TP angle of 8-10 percent at idle, and 76-77 percent at wide open throttle (WOT).

An intermittent malfunction may be caused by fault in the TP sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

Test Description

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

  1. The Diagnostic System Check - Vehicle 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. This step determines if DTC P0123 is the result of a hard failure or an intermittent condition.

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

With the throttle closed, select the TP sensor parameter on the scan tool.

Is the throttle position (TP) sensor percentage within the specified value?

7-11%

Go to Step 3

Go to Step 4

3

  1. Perform the scan tool Clear DTC Information function.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Freeze Frame conditions as specified.

Does DTC P0123 set?

--

Go to Step 4

Go to Diagnostic Aids

4

Is a DTC P0118 or P0453 also set?

--

Go to Step 7

Go to Step 5

5

  1. Disconnect the TP sensor electrical connector.
  2. Connect a test lamp to B+ and the ground circuit of the TP sensor.

Did the test lamp illuminate?

--

Go to Step 6

Go to Step 8

6

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

Did you find and repair a condition?

--

Go to Step 13

Go to Step 12

7

  1. Test for an open in the TP sensor ground circuit between SP108 and the powertrain control module (PCM).
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 13

Go to Step 11

8

  1. Test for an open in the TP sensor ground circuit between SP108 and the TP sensor.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 13

Go to Step 9

9

  1. Test for an intermittent or a poor electrical connection at the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair the circuit as necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 13

Go to Step 10

10

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

Did you complete the replacement?

--

Go to Step 13

--

11

  1. Test for an intermittent or a poor electrical connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair the circuit as necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 13

Go to Step 12

12

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 13

--

13

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 14

Go to Step 2

14

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 - Vehicle in Vehicle DTC Information

System OK