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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2004 🢒 GTO 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P1121

Circuit Description

The throttle position (TP) sensor is used by the powertrain control module (PCM) in order 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, and a signal 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 more than 4 volts through the TP sensor signal circuit. If the PCM detects an intermittent, excessively-high signal voltage, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC.

DTC P1121 Throttle Position (TP) Sensor Circuit Intermittent High Voltage

Conditions for Running the DTC
    • The ignition is ON.
    • DTCs P0641 and P0651 are not set.
    • DTC P1121 runs continuously once the above conditions are met.

Conditions for Setting the DTC
    • The TP sensor voltage is more than 4.8 volts.
    • The intermittent condition exists for more than 1 second during a 2 second period.

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

Electromagnetic interference (EMI) can cause an intermittent DTC. Inspect the related circuits for being too close to the secondary ignition wires and to the generator.

If the engine has sat overnight, the engine coolant temperature (ECT) and the intake air temperature (IAT) values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance .

For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. This test will determine an intermittent faulty TP sensor utilizing the DMMs MIN MAX, 100 millisecond capture mode.

DTC P1121 Throttle Position (TP) Sensor Intermittent High Voltage

Step

Action

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-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Test all 5-volt reference circuits for an intermittent short to voltage.

  1. Turn OFF the ignition.
  2. Disconnect the TP sensor.
  3. Connect a DMM between the TP sensor 5-volt reference circuit at the TP sensor harness connector and ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Lightly touch and move the related engine wiring harnesses and connectors for all 5-volt reference circuits while observing voltage. Any change in voltage indicates the area where a short to voltage may be found. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 3

3

Test the TP sensor signal circuit for an intermittent short to voltage.

  1. Turn OFF the ignition.
  2. Connect a DMM between the TP sensor signal circuit at the TP sensor harness connector and ground.
  3. Turn ON the ignition, with the engine OFF.
  4. Lightly touch and move the related engine wiring harnesses and connectors while observing voltage. Any change in voltage indicates the area where a short to voltage may be found. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 4

4

Test the TP sensor low reference circuit for an intermittent open or high resistance.

  1. Turn OFF the ignition for 30 seconds.
  2. Connect a DMM between the TP sensor low reference circuit at the TP sensor harness connector and ground.
  3. Lightly touch and move the related engine wiring harnesses and connectors while observing resistance. Any change in resistance indicates the area where an open or high resistance may be found. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 5

5

Inspect for poor connections at the TP sensor harness connector. 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 9

Go to Step 6

6

Inspect for poor connections at the PCM harness connector. 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 9

Go to Step 7

7
  1. Connect two jumper wires at the TP sensor, one at the signal terminal, and one at the 5-volt reference terminal.
  2. With a DMM set to the 40k  ohms scale, connect the DMM to the jumper wires.
  3. Ensure a good, proper connection at the TP sensor and DMM test leads.
  4. Press the MIN MAX button on the DMM.
  5. Slowly depress the accelerator pedal to wide open throttle (WOT) and back to the closed throttle position several times.
  6. Press the MIN MAX button and record the MAX reading.
  7. Press the MIN MAX button again and record the MIN reading.
  8. Remove the jumper wire at the 5-volt reference terminal. Connect the jumper wire to the low reference terminal. Repeat steps 2-7.

Did you record a MAX value of OL or record a MIN value of 0 ohms in either test?

Go to Step 8

Go to Intermittent Conditions

8

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

Did you complete the replacement?

Go to Step 9

--

9
  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 10

Go to Step 2

10

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