P0120🔧 Air intake / throttle position sensorStop and fix promptly

P0120: Throttle Position Sensor A Circuit Malfunction (Meaning, Causes, Fixes)

Reviewed 2026-10-24 · Based on 2 cited source(s)

What P0120 means

The throttle position sensor is a potentiometer on the throttle body that reports how far the throttle blade is open. It usually has three wires: a 5-volt reference from the PCM, a ground, and a signal wire back to the PCM. OBD-Codes.com says the signal is about 0.45 volts with the throttle closed and approaches 5 volts at wide open throttle, and P0120 sets when the PCM sees a voltage outside the normal range. On some models the PCM also compares throttle position with manifold pressure (MAP) and can set P0120 if they don't change together. RepairPal defines the code more broadly as the Throttle/Pedal Position Sensor/Switch 'A' circuit, because on drive-by-wire cars the accelerator pedal also has a position sensor that tells the PCM how far you're pressing, and the throttle sensor confirms the throttle opened as requested. The sources differ slightly on the closed-throttle voltage (about 0.45 volts per OBD-Codes.com, usually 0.5 to 1 volt per RepairPal) and on symptoms: OBD-Codes.com lists misfiring, poor idle and stalling, while RepairPal says many cars show no symptom besides the check engine light. P0120 is a generic OBD-II code; related codes P0121 through P0124 cover range/performance, low, high and intermittent faults in the same circuit.

Severity: can I keep driving?

Stop and fix promptly

Get this diagnosed promptly. RepairPal rates P0120 'Urgent' and says the computer may put the car in limp home mode, limiting speed to 20 mph or less. OBD-Codes.com lists stalling and poor idle as possible symptoms. If the engine stalls, won't idle, or the car won't accelerate normally, don't drive it in traffic; have it towed or diagnosed first.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Faulty throttle position or pedal position sensor (both sources)
  2. Corroded TPS or MAP sensor connector, or chafed, misrouted or damaged wiring (both sources)
  3. Sticking throttle return spring (OBD-Codes.com)
  4. Dirty or carbon-filled throttle bore (RepairPal)
  5. Torn or jammed floor mats interfering with the pedal (RepairPal)
  6. Faulty PCM, which is less common (OBD-Codes.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Make sure the floor mat isn't bunched up or caught under the accelerator pedal (RepairPal).
  2. Inspect the throttle body for heavy carbon buildup and check that the throttle snaps closed freely without a sticking return spring (both sources).
  3. Check the sensor connector and harness for corrosion, loose terminals, or wiring rubbed through where it's routed (both sources).
  4. With a scan tool, key on and engine off, watch the throttle position voltage while slowly pressing the pedal. It should start low (about 0.45 volts per OBD-Codes.com, 0.5 to 1 volt per RepairPal) and rise smoothly to about 4.5 to 5 volts with no drop-outs or glitches.
  5. Do a wiggle test: watch the live voltage while moving the wiring and connector. If the reading jumps, repair the wiring before replacing the sensor (RepairPal).

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The glitch is intermittent and doesn't show on a scan tool; both sources say a lab scope may be needed to catch a drop-out in the sensor signal
  • Some throttle position sensors need fine adjustment with a digital multimeter after replacement; OBD-Codes.com suggests a shop if you're not comfortable doing that
  • Checking the 5-volt reference, ground and signal circuits for opens or shorts, which OBD-Codes.com describes doing with a fused jumper wire
  • Drive-by-wire cars where the throttle sensor must be compared with the pedal sensor with the engine running or on a road test (RepairPal)
  • RepairPal warns sensors are often replaced when the real problem was a dirty throttle body, a poor connection, chafed wiring, or a damaged floor mat

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is it safe to drive with P0120?

RepairPal rates it 'Urgent' and says the car may go into limp home mode at 20 mph or less. OBD-Codes.com lists stalling and poor idle. Get it diagnosed promptly, and don't drive in traffic if the engine stalls or won't accelerate normally.

What's the difference between P0120 and P0122 or P0123?

P0120 is the general 'A' circuit malfunction code. RepairPal lists P0121 for range/performance, P0122 for circuit low, P0123 for circuit high and P0124 for intermittent faults in the same sensor circuit.

Can a floor mat really cause P0120?

RepairPal lists torn or jammed floor mats as a common trigger and says the pedal position sensor is sometimes replaced when the mat was the real problem, so check it first.

How much does it cost to fix P0120?

Neither source gives a repair cost. The fix can range from cleaning the throttle body or repairing a connector to replacing the sensor, so get it diagnosed and ask for a written estimate.

Sources

  1. OBD-Codes.com: P0120 Throttle Position Sensor/Switch (TPS) A Circuit Malfunction
  2. RepairPal: P0120 Throttle/Pedal Position Sensor/Switch "A" Circuit (rated Urgent)

Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.