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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0123

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 3 circuits:

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

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor 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 greater than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively high signal voltage, this diagnostic trouble code (DTC) will set.

Conditions for Running the DTC

Ignition is ON.

Conditions for Setting the DTC
    • The TP sensor signal voltage is more than 4.9 volts.
    • The above conditions are present for more than 1 second.

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.

Test Description

The number below refers to the step number on the diagnostic table:

  1. An internally shorted exhaust gas recirculation (EGR) valve could cause a high voltage condition on the 5-volt reference circuit.

DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage

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. Turn ON the ignition, with the engine OFF.
  2. Use a scan tool in order to observe the throttle position (TP) sensor voltage parameter with the throttle closed.

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

4.9 V

Go to Step 4

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records that you observed.

Does the DTC fail this ignition?

--

Go to Step 4

Go to DTC P1121

4
  1. Turn OFF the ignition.
  2. Disconnect the TP sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Use a scan tool in order to observe the TP sensor voltage parameter.

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

0 V

Go to Step 5

Go to Step 8

5

Use a DMM in order to test the TP sensor 5-volt reference circuit for voltage.

Does the DMM indicate that the TP voltage parameter is at the specified value?

5 V

Go to Step 6

Go to Step 9

6
  1. Connect a test lamp to battery positive voltage.
  2. Probe the low reference circuit of the TP sensor with the test lamp.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 7

7

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

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

8

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

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

9

Test all 5-volt reference circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

10

Inspect for poor connections at the harness connector of the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 12

11

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and 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.

Does the DTC run and pass?

--

Go to Step 15

Go to Step 2

15

Use a scan tool, in order to 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