Automotive / Parts Accessories
Toyota P0120 Throttle/Pedal Position Sensor/Switch A Circuit Malfunction Diagnostic Guide
Diagnostic procedure for Toyota DTC P0120, covering circuit inspection, voltage testing for throttle position sensors, and ECM troubleshooting steps.
Table of contents
Quick guide from the manual
This document provides diagnostic procedures for the Toyota DTC P0120, which indicates a malfunction in the Throttle/Pedal Position Sensor/Switch A circuit. The primary goal is to identify whether the issue lies within the sensor, the wiring harness, or the Engine Control Module (ECM).
Circuit Description
The throttle position sensor is mounted on the throttle body and monitors the throttle valve opening angle. The ECM supplies voltage to the sensor and receives a signal (VTA) that varies based on the valve position:
- Fully closed: 0.3 – 1.0 V
- Fully open: 2.7 – 5.2 V
The ECM uses this signal to manage air-fuel ratio correction, power increase, and fuel-cut control. A DTC P0120 is triggered if the VTA signal remains below 0.1 V or above 4.9 V.
Inspection Procedure
Follow these steps to diagnose the fault:
- Scan Tool Check: Connect an OBD II scan tool or Toyota hand-held tester to the DLC3 port. Read the throttle valve opening percentage. Normal values are approximately 10% when closed and 75% when fully open.
- Sensor Connector Voltage: Disconnect the throttle position sensor connector. With the ignition ON, measure the voltage between terminal 2 and body ground. The expected range is 4.5 – 5.5 V.
- Sensor Inspection: If the wiring is correct, inspect the throttle position sensor itself according to the vehicle's specific service manual (SF-29).
- ECM Connector Voltage (VTA): Measure the voltage between terminals VTA and E2 at the ECM connector. Expected values are 0.3 – 1.0 V (closed) and 2.7 – 5.2 V (open).
- ECM Connector Voltage (VCC/VC): Measure the voltage between terminals VCC (or VC) and E2 at the ECM connector. The expected range is 4.5 – 5.5 V.
Troubleshooting Notes
If DTCs P0110, P0115, and P0120 appear simultaneously, the E2 (sensor ground) circuit may be open. Always check the freeze frame data to understand the engine conditions at the time the malfunction occurred.
Manufacturer information
Toyota Motor Corporation
Practical help
Common problems
DTC P0120 triggered
Check for open or short circuits in the throttle position sensor wiring, test the sensor itself, or inspect the ECM.
Simultaneous P0110, P0115, and P0120 codes
This often indicates an open E2 (sensor ground) circuit.
Before use
- Ensure you have an OBD II scan tool or Toyota hand-held tester.
- Verify the ignition switch is in the ON position for voltage measurements.
- Access the ECM connector (requires removing the glove compartment).
- Identify if your vehicle is California Spec or non-California Spec, as wiring terminals differ.
Specs in practice
- VTA Signal Voltage
- 0.3–1.0V (closed) to 2.7–5.2V (open); indicates throttle angle to the ECM.
- Sensor Supply Voltage
- 4.5–5.5V; the reference voltage provided by the ECM to the sensor.
Model compatibility
- This manual is specific to the 2000 Toyota Tacoma with the 5VZ-FE engine.
- Terminal configurations for VCC/VC and VTA vary between California and non-California vehicle specifications.
Manual page author
Michael Turner
Technical manual editor
Reviews PDF manuals for structure, safety notes, and practical product details so readers can find the right information quickly.