P0123 — Throttle Position Sensor/Switch A Circuit High Input

P0123 — Throttle Position Sensor/Switch A Circuit High Input. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: wiring or connector faults in the throttle circuit, dirty throttle body or stuck throttle plate, failed electronic throttle motor.

powertrain (engine/transmission)

Is it safe to drive?

Limited throttle operation may be present P0123 can affect idle control and throttle response, so the vehicle may be drivable but should be driven cautiously. Avoid heavy acceleration or traffic if the engine stumbles, idles extremely high, enters reduced-power mode, or repeatedly sets P0123.

Typical symptoms

The check-engine light illuminates and the scanner stores P0123
Engine idle speed is unusually high, unstable, or drops unexpectedly
The engine hesitates or responds sluggishly when accelerator pedal input is requested
The vehicle may enter a reduced-power or throttle-limiter mode
The engine can stall or stumble at low throttle openings
P0123 may remain stored or return after the fault is cleared

Common causes

A throttle position sensor A signal circuit with an open connection or high-resistance corrosion
The throttle position sensor signal wire shorted to battery voltage, driving the input above the ECU's calibrated high limit
A loose, damaged, or moisture-contaminated throttle position sensor connector
A defective throttle position sensor whose internal potentiometer no longer provides a valid voltage range
An incorrect or weak 5-volt reference voltage caused by a wiring or engine-control-module problem
A poor sensor ground or damaged ECU-side wiring allowing the P0123 high-input condition to register

How to diagnose with an OBD scanner

Inspect the sensor and connector Locate throttle position sensor A using the vehicle wiring diagram. Inspect its connector and harness for pushed-back terminals, bent pins, green corrosion, heat damage, oil contamination, or a cable chafing against a moving part.
Check the sensor circuit With the ignition on and the engine off, back-probe the sensor reference, ground, and signal wires. Confirm that the reference is approximately 5 volts, ground is close to 0 volts, and the signal changes smoothly as the throttle is operated. Do not assume a three-wire pinout; verify it for the specific vehicle.
Read P0123 with an OBD scanner Connect an OBD scanner such as an ELM327 adapter or AIScanAuto, open diagnostic trouble codes, and verify that P0123 is active or pending. Review freeze-frame data and live throttle-position readings for an implausible voltage, abrupt signal jumps, or a reading that does not correspond to throttle movement.
Isolate an open or shorted circuit Measure the P0123 signal line from the ECU to the sensor for continuity and excessive resistance with the harness disconnected. Check for short-to-battery voltage if the signal remains abnormally high. Repair damaged wiring or terminals, or service the connector pins, before condemning the sensor.
Test or replace the sensor If the wiring, connector, reference voltage, and ground are normal, test throttle position sensor A with the specified procedure. Replace the sensor or ECU-side driver if it fails, then clear P0123 and confirm that live data remains plausible and the code does not return.

Approximate repair cost

Independent-shop estimates are typically $100-$400 for P0123 diagnosis and repair. A throttle position sensor replacement may add roughly $60-$250 including labor, while harness or connector repairs can add $75-$300 depending on access and damage. These USD figures are estimates and vary by region, vehicle design, and parts availability.

Common questions

What does P0123 specifically mean?

P0123 means the ECU detected a voltage above the expected high-input limit on the throttle position sensor A signal circuit. It points to the sensor, connector, or wiring rather than a general throttle-system condition.

Can I drive with P0123 stored?

The vehicle may still operate because the controller can use a fail-safe throttle setting, but stalling, high idle, or reduced power can create a safety concern. Diagnostic repair is advisable, especially if the fault repeatedly returns.

Should I replace the throttle position sensor first?

Not always. P0123 can also result from corroded terminals, an open circuit, a short to battery voltage, or a bad reference or ground, so the wiring and connector should be checked before replacing the sensor.

Why does P0123 return after the code is cleared?

P0123 returns when the high signal condition remains or reappears. Inspect the harness and connector, verify reference voltage and ground, and monitor the sensor signal while operating the throttle before clearing the code again.

When your vehicle's engine control unit detects a voltage signal from the throttle position sensor that sits abnormally high—essentially near battery voltage—the system logs trouble code P0123. This code falls within the OBD2 powertrain category and specifically points to a "Circuit High Input" condition on Throttle Position Sensor/Switch A. The ECU expects this sensor to produce a varying voltage that corresponds to how far the throttle plate is open; when that signal climbs outside its normal operating range and stays there, the module registers the fault.

The throttle position sensor plays a direct role in how your engine manages air intake. It feeds real-time data about throttle angle to the ECU, which uses that information alongside other sensor inputs to calculate fuel delivery, transmission shifting points, and in some cases, traction control responses. Because the module continuously monitors this circuit, any persistent deviation from expected voltage levels—typically beyond roughly 4.5 volts when the sensor should be producing a lower range—triggers P0123 after the condition meets the manufacturer's defined drive cycle threshold. The stored freeze frame data captures exactly what the engine was doing at the moment the fault first appeared, giving you a diagnostic snapshot to work from.

Setting P0123 tells you the throttle circuit is reporting an impossible reading. Either the sensor itself has failed in a way that forces the signal line high, a short exists somewhere in the wiring that feeds unwanted voltage into that circuit, or a ground connection the sensor relies on has broken. The root cause matters because it determines whether you're dealing with a simple wiring issue or a component that needs replacement.

Common symptoms of P0123

The Check Engine Light illuminates and remains on
Engine falls into limp-home mode with noticeably reduced power output
Idle speed feels rough, higher than normal, or erratic
Engine stalls when decelerating or coming to a stop
Throttle response feels sluggish or delayed when pressing the accelerator
In some vehicles, electronic stability or traction control warning lights may also activate

What causes P0123?

Failed throttle position sensor pulling the signal circuit high
Signal wire shorted directly to battery positive voltage
Open or corroded ground return circuit for the throttle position sensor
Dirty or carboned-up throttle body causing the plate to stick or move incorrectly
Wiring harness or connector damage in the throttle position sensor circuit
Faulty MAF or MAP sensor affecting intake air metering calculations
Failed electronic throttle motor in drive-by-wire systems
Intake air leaks downstream of the mass airflow sensor

How to diagnose P0123

Connect an OBD2 scanner and confirm P0123 is stored in the ECU memory. Save the associated freeze frame data—this record shows RPM, engine load, coolant temperature, and vehicle speed when the fault occurred and serves as your reference point throughout the diagnostic process.
Pull all stored and pending codes beyond P0123. Related trouble codes in the same circuit or connected systems often reveal the true underlying cause. Cross-reference any relevant technical service bulletins for your specific make and model through the manufacturer portal or nhtsa.gov; some P0xxx codes have documented software updates or known fixes.
Perform a thorough visual inspection of the throttle position sensor wiring harness and connectors. Look for damaged insulation, broken wires, corrosion buildup, loose terminals, or evidence of prior repairs that may have been completed improperly.
With the sensor connector unplugged, back-probe the signal circuit at the harness side and measure voltage using a multimeter. A reading near battery voltage with the sensor disconnected confirms a short to power in the wiring. If the reading drops to normal reference voltage with the sensor unplugged, the sensor itself has failed.
Inspect the throttle body for carbon deposits and verify the throttle plate moves freely through its full range of motion. Clean the throttle body if deposits are present, then clear the code and test drive the vehicle under the freeze frame conditions to confirm whether P0123 returns.
Monitor throttle position percentage and MAF/MAP sensor readings in live data while slowly pressing and releasing the accelerator pedal. Values should transition smoothly across the range; any sudden jumps, flatlines, or erratic behavior points to sensor or wiring faults.

Repair options with cost estimates

Replace MAF or MAP sensor: $150–$400 (parts and labor at independent shop rates)
Clean throttle body: $80–$200
Replace throttle body assembly: $250–$700

These repair scenarios cover the most common root causes of P0123. Sensor replacement addresses failed components pulling the circuit high, while throttle body service resolves performance issues stemming from carbon buildup or mechanical binding.

How much does it cost to fix P0123?

Total repair costs for P0123 typically fall between $80 and $700 depending on which component is responsible. Cleaning the throttle body represents the least expensive and most frequently successful first step, while full throttle body replacement represents the costliest scenario. MAF or MAP sensor replacement falls in the middle range. Spending time on careful diagnosis before purchasing parts prevents unnecessary spending—replacing a wiring harness or sensor when the real issue is simply a dirty throttle body wastes money and creates frustration.

Can you drive with P0123?

Drive with caution. P0123 often triggers limp-home mode, which significantly reduces engine power and limits acceleration. This reduced-power state allows you to reach a repair facility but is not suitable for highway driving or situations requiring full throttle response. If the throttle pedal becomes unresponsive or the engine stalls repeatedly, stop driving immediately and arrange for towing. Continuing to operate a vehicle in this condition poses safety risks to you and other road users.