P0120 Code: Throttle/Pedal Position Sensor/Switch A Circuit Malfunction
Note: We do not currently have verified model-specific diagnostic data for the Lexus Is. The symptoms and fixes listed below are the standard generic OBD2 guidelines for the P0120 code. Always consult a factory service manual before replacing parts.
What does this mean?
Code P0120 indicates a malfunction in the Throttle Position Sensor (TPS) 'A' circuit. The PCM monitors the TPS to determine throttle blade angle.
Diagnostic system: Sensor circuit and live data
On a Lexus Is, the P0120 code should be diagnosed as part of the sensor circuit and live data group. Related codes and live data from this same system can change the repair priority, so avoid replacing parts from the code name alone.
Most Common Causes for Lexus Is
- Faulty throttle position sensor (TPS)
- Damaged, chafed, or broken wiring harness
- Corroded or loose electrical connector
- Dirty or faulty throttle body
Symptoms to Watch For
- Check Engine Light is illuminated
- Poor acceleration or sluggish response
- Engine surging or fluctuating RPM
- Engine stalling or dying unexpectedly
- Erratic or fluctuating idle speed
- Vehicle enters reduced power / limp mode
Before replacing parts, check these first
- Inspect the connector for corrosion, broken locks, oil intrusion, or heat damage.
- Verify 5V reference, ground, and signal with a multimeter where applicable.
- Compare live sensor data to realistic engine temperature, pressure, airflow, or throttle values.
- Check for blown fuses, weak battery voltage, and damaged connectors before buying major parts.
How to Diagnose
Common Mistakes
Replacing the named sensor without testing power, ground, signal, and wiring continuity first. Always confirm the fault with freeze-frame data, live data, visual inspection, and circuit checks before spending money on parts.
Frequently Asked Questions
Can I drive with the P0120 code?
If the check engine light is solid, you can usually drive to a safe location or mechanic. If the light is flashing, pull over immediately to prevent catastrophic engine or catalytic converter damage.
Will the P0120 code clear itself?
Once the underlying problem is fixed, the engine computer will run its self-checks. If it passes over several drive cycles, the light will turn off automatically. You can also clear it immediately using an OBD2 scanner.
Will this code fail an emissions test?
Yes. If the Check Engine Light is on due to the P0120 code, your Lexus will automatically fail an OBD2 plug-in emissions or smog test.
What should I check first for P0120?
Inspect the connector for corrosion, broken locks, oil intrusion, or heat damage. Verify 5V reference, ground, and signal with a multimeter where applicable. Compare live sensor data to realistic engine temperature, pressure, airflow, or throttle values.
Join the Discussion
Repair Estimate
Fuse, connector, wiring, cleaning, or basic inspection
Major component replacement after live data and circuit tests confirm failure
Includes parts and labor. May vary by location.
Sensor replacement can be moderate cost, but wiring and connector repairs are common and cheaper.
DIY Difficulty
Can usually be performed at home with basic hand tools.