Fuel & air metering · Powertrain · generic (SAE-defined)
P0120: Throttle/Pedal Position Sensor/Switch "A" Circuit
P0120 means the engine computer detected an electrical problem in the "A" throttle or pedal position sensor circuit, which reports how far the throttle or accelerator is opened.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0120 sets
The throttle position sensor (TPS) or pedal position sensor sends a voltage signal that changes as the throttle or pedal moves. The powertrain control module (PCM) monitors that signal for presence and plausibility. If the "A" signal is missing, erratic or outside its normal range in a way not covered by a more specific high or low code, P0120 sets. On electronic throttle systems, the PCM usually limits power as a precaution.
Common causes of P0120
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Failed throttle position or pedal position sensor
- Loose, corroded or damaged connector
- Open or shorted sensor wiring
- Problem with the sensor reference voltage or ground
- Faulty electronic throttle body assembly
- PCM fault (rare)
P0120 symptoms
- Check engine light on
- Reduced power or limp mode
- Hesitation, surging or erratic idle
- Stalling
- Electronic throttle control warning light on some vehicles
How P0120 is diagnosed
- Scan for codes, including reference voltage and other throttle codes
- Inspect the throttle body and pedal sensor connectors and wiring
- Check reference voltage and ground at the sensor
- Watch the TPS or pedal signal in live data while slowly opening the throttle; look for dropouts
- Scope the signal for glitches if live data looks normal
- Repair wiring or replace the sensor or throttle body, then perform any required relearn
Typical fixes for P0120
- Replace the throttle position sensor
- Replace the electronic throttle body assembly
- Replace the accelerator pedal position sensor
- Repair wiring or connector damage
- Perform a throttle relearn procedure
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Definitions of sensor "A" can vary by manufacturer; check factory service information.
Related codes & warning lights
P0120 FAQ
What does code P0120 mean?
P0120 means the engine computer detected an electrical problem in the "A" throttle or pedal position sensor circuit, which reports how far the throttle or accelerator is opened. The standard definition is "Throttle/Pedal Position Sensor/Switch "A" Circuit."
Can I drive with a P0120 code?
Drive only as far as needed to get it repaired. Many vehicles enter a reduced-power mode with this code, and erratic throttle response can make acceleration unpredictable in traffic.
Does P0120 refer to the throttle or the gas pedal?
The SAE wording covers both. On many electronic throttle systems "A" is a throttle body sensor, but some manufacturers use it for the pedal; check factory service information.
Do I need a relearn after replacing the throttle body?
Many vehicles require an idle or throttle relearn after replacement or cleaning so the PCM can learn the new closed position.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.