P0123🔧 Engine management / throttle and accelerator pedal sensorsStop and fix promptly

P0123: Throttle/Pedal Position Sensor A Circuit High (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 2 cited source(s)

What P0123 means

The throttle position sensor sits on the throttle body and tells the engine computer how far the throttle is open; on cars with electronic throttle, a pedal position sensor in the accelerator pedal assembly does a similar job. OBD-Codes.com explains that it's usually a three-wire sensor with a 5-volt reference, a ground and a signal wire. With the throttle closed the signal is near 0.45 volts, and at wide open throttle it approaches 5 volts. When the computer sees a voltage above the normal upper limit, P0123 sets. RepairPal says the same thing more briefly: the code triggers when the 'A' circuit has high output. P0123 is the opposite of P0122 (voltage too low), and P0121 covers a reading that's in range but doesn't make sense. The sources differ on symptoms: OBD-Codes.com lists rough idle, high idle and surging, while RepairPal says in many cases no abnormal symptoms are noticed, with hard starting or hesitation in some cases. They also differ on causes: OBD-Codes.com names a TPS that isn't mounted securely, a short to ground or another wire, and a damaged engine computer, while RepairPal adds a dirty or carbon-filled throttle body and torn or jammed floor mats. OBD-Codes.com uses the older name 'Throttle Position Sensor/Switch A Circuit High Input'; RepairPal uses 'Throttle/Pedal Position Sensor/Switch A Circuit High'. It is a generic code that can appear on any OBD-II vehicle.

Severity: can I keep driving?

Stop and fix promptly

Get it diagnosed soon and drive carefully. RepairPal rates P0123 Urgent and says the engine computer may limit the car to about 20 mph or less (limp home mode) because it can't accurately tell how much power you're asking for. OBD-Codes.com lists rough idle, high idle and surging as possible symptoms. If the car surges, idles high or won't accelerate normally, avoid highway and heavy-traffic driving until it's checked.

Common symptoms

Likely causes

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

  1. Faulty throttle or pedal position sensor (both sources)
  2. Throttle position sensor not mounted securely (OBD-Codes.com)
  3. Sensor circuit shorted to ground or another wire (OBD-Codes.com), or chafed or corroded wiring and connections (RepairPal)
  4. Dirty or carbon-filled throttle body (RepairPal)
  5. Torn or jammed floor mat interfering with the pedal (RepairPal)
  6. Damaged engine computer (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. Check for technical service bulletins for your vehicle first. OBD-Codes.com says your problem may be a known issue with a known fix.
  2. If there are no symptoms, OBD-Codes.com suggests clearing the code and seeing if it comes back.
  3. Check that the floor mat isn't bunched up, torn or pushing on the accelerator pedal. RepairPal lists this as a cause and says pedal sensors are sometimes replaced when the mat was the real problem.
  4. Make sure the throttle position sensor is mounted securely, then inspect all its wiring and connectors for breaks, rubbing against other parts, chafing and corrosion. OBD-Codes.com says that if the engine stumbles or hesitates, the problem is more than likely in the wiring.
  5. Check the sensor voltage using your service manual's specs. OBD-Codes.com says a reading that spikes or is too high (over 4.65 volts with key on, engine off) points to a problem.
  6. Look inside the throttle body for heavy carbon buildup and clean it following your manufacturer's procedure. RepairPal warns the throttle position sensor is often replaced when a dirty throttle body was the real problem.

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 car is in limp mode, surges, or won't accelerate normally
  • You don't have your car's voltage specs or a meter to test the circuit
  • The wiring, connector, mounting and floor mat check out
  • The code comes back after you've replaced the sensor

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

Can I drive with P0123?

Carefully, and not for long. RepairPal rates it Urgent and says the car may be limited to about 20 mph in limp home mode, and OBD-Codes.com lists surging and a high idle as possible symptoms.

What's the difference between P0121, P0122 and P0123?

All three are 'A' circuit throttle or pedal position sensor codes. P0123 means the voltage is too high, P0122 means it's too low, and P0121 means the reading doesn't make sense for what the engine is doing even if the voltage is in range.

What voltage should a throttle position sensor read?

OBD-Codes.com says the signal is typically near 0.45 volts with the throttle closed and approaches 5 volts at wide open throttle, and that over 4.65 volts with key on, engine off indicates a problem. Check your service manual for your car's exact specs.

Can a floor mat or dirty throttle body cause P0123?

RepairPal lists both as common causes and says sensors are often replaced when the real problem was a dirty throttle body or a torn or jammed floor mat, so they're worth checking first.

How much does it cost to fix P0123?

Neither source gives a repair cost for P0123. It can range from moving a floor mat or fixing a wire to a new sensor, so get it diagnosed first.

Sources

  1. OBD-Codes.com: P0123 Throttle Position Sensor/Switch A Circuit High Input
  2. RepairPal: P0123 Throttle/Pedal Position Sensor/Switch A Circuit High (rated Urgent)

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.