P1121 TOYOTA – Accelerator Pedal Position Sensor Range/Performance Problem

Toyota Code P1121: Possible Causes

• Faulty Accelerator Pedal Position Sensor: An internal malfunction of the sensor can distort the data sent to the computer.

• Electrical Harness Problem: An open circuit, short circuit, or damaged wires in the harness connected to the sensor.

• Defective Electrical Connections: Oxidation, corroded, bent, or improperly engaged pins in the circuit connectors.

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Common Symptoms

• 🔥 Check Engine Light On (or pre-ignition in “limp home” mode).

• Unstable idle or delayed throttle response.

• Loss of power or reduced performance mode (engine speed limitation).

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Meaning of Code P1121
The Accelerator Pedal Position Sensor (APPS) is located on the throttle body and integrates two potentiometers to accurately measure the pedal opening angle. These sensors send variable signals (0-5 V) to the VPA and VPA2 terminals of the engine control module (ECM), allowing it to control the throttle opening based on accelerator pedal input.

In case of an anomaly (such as P1121), the ECM can:

1. Activate the check engine light and record the fault code.

2. Switch to a safe mode (throttle closed by return spring, reduced power).

3. If code P1120 is also present, cut power to the throttle motor and deactivate the magnetic clutch.

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Diagnostic and Repair Procedure

1. Visual Inspection

   • Check the sensor’s electrical harness: Look for cut, burned, or damaged insulation wires.

   • Inspect the connectors: Clean oxidized pins, ensure they are properly aligned and secured.

2. APPS Sensor Test

   • Using a multimeter, measure the voltage between the VPA/VPA2 terminals and ground. The voltage should gradually vary from 0.5 V to 4.5 V when the pedal is depressed.

   • Compare the values with those specified in the Toyota technical manual.

3. Reference and Ground Check

   • Ensure the sensor receives a stable 5 V power supply and that the circuit ground is intact.

4. Replacement or Repair

   • If the sensor is faulty, replace it with an OEM part.

   • Repair or replace the damaged harness using waterproof connectors to prevent future corrosion.

5. Code Clearing and Test

   • Use a diagnostic tool to clear the P1121 code.

   • Perform a road test to confirm the symptoms have disappeared.

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Important Tip
If the problem persists after these checks, consult a professional equipped with an advanced diagnostic tool. ECM malfunctions or throttle calibration errors may require specific expertise.

Note: Regular maintenance of electronic systems prevents the majority of faults related to sensors or connections.