P0122 — Throttle Position Sensor/Switch A Circuit Low Input

P0122 — Throttle Position Sensor/Switch A Circuit Low Input. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: failed electronic throttle motor, dirty throttle body or stuck throttle plate, contaminated or failed MAF/MAP sensor.

powertrain (engine/transmission)

Is it safe to drive?

Drive cautiously if the engine runs normally P0122 can affect throttle response and engine stability. Avoid extended or aggressive driving until the fault is repaired, and stop driving if the engine stalls, loses substantial power, or runs erratically.

Typical symptoms

P0122 may cause hesitation, surging, or difficulty maintaining a steady engine speed.
A low throttle-position signal can produce unstable idle speed or an unusually high idle.
The engine may enter reduced-power or fail-safe operation when P0122 is active.
Stalling, especially when releasing the accelerator, can occur with a severe low-input condition.
The check-engine light may illuminate with P0122 stored in the powertrain controller.

Common causes

A short to ground in the throttle position sensor A signal wire can cause the controller to record P0122.
Corrosion, a loose terminal, or water intrusion in the throttle position sensor connector can create an abnormally low signal.
A defective throttle position sensor may report an implausibly low voltage even when the throttle plate is not closed.
An open circuit or high resistance in the sensor reference or ground connection can make the P0122 signal appear low.
Damaged wiring near the throttle body can intermittently pull the sensor output below the expected range.
A powertrain control module or internal circuit failure is possible after wiring and sensor faults have been ruled out.

How to diagnose with an OBD scanner

Confirm the code and freeze data Connect an OBD scanner, ELM327 adapter, or AIScanAuto and read stored and pending codes. Confirm P0122 and inspect freeze-frame data for throttle position, engine speed, and operating temperature.
Inspect the sensor and connector Locate the throttle position sensor on the throttle body. Examine its connector and harness for backed-out pins, corrosion, melting, oil contamination, or a wire damaged by moving components.
Test reference, ground, and signal With the ignition on, back-probe the sensor connector and measure its reference voltage, ground voltage, and throttle-position output. Compare the readings with the manufacturer specifications while moving the throttle plate.
Isolate a wiring short If the signal remains abnormally low, disconnect the sensor and check whether the line becomes high-impedance. A persistent low reading points to a harness short; a correct reading with the sensor disconnected points toward the sensor.
Repair and verify operation Repair the damaged connector or wiring, replace the failed sensor, or address the confirmed control-module fault. Clear the code, then verify that P0122 does not return and that throttle response and idle are normal.

Approximate repair cost

A typical independent-shop estimate for diagnosing and repairing P0122 is about USD $120-$500, depending on whether the sensor, connector, wiring, or control module requires service. These figures are estimates and vary by region.

Common questions

What does P0122 specifically mean?

P0122 means the controller detected a throttle position sensor A circuit voltage lower than the expected range. It describes an electrical signal problem, not necessarily a physically closed throttle.

Is P0122 always caused by a bad throttle position sensor?

No. A shorted signal wire, damaged connector, poor sensor ground, or defective sensor can all produce P0122, so the wiring should be tested before replacing parts.

Can I drive my vehicle with P0122 stored?

You may drive cautiously if the engine runs smoothly and power is normal, but P0122 can cause surging, fail-safe operation, or stalling. Repair it promptly and avoid driving if those symptoms occur.

Why does the throttle reading look incorrect during a P0122 scan?

The low input can make the controller report a throttle angle that does not match the actual pedal or throttle-plate position. Confirm the sensor circuit with voltage measurements rather than relying only on scan data.

The engine control module (ECM) logs code P0122 when it notices something wrong with how the throttle position sensor communicates. Specifically, P0122 stands for Throttle Position Sensor/Switch A Circuit Low Input — the sensor circuit is putting out a voltage that's too low, hovering near ground potential instead of the expected range. The throttle position sensor tells the computer exactly how far the accelerator pedal is pressed, and that information controls everything from fuel delivery to shifting points. When the signal collapses, the ECM can no longer trust what it's hearing from the sensor.

P0122 triggers when the voltage on that specific circuit sits below the minimum threshold for a sustained period. A few things can cause this: the sensor itself may have failed and is pulling the signal to ground, a wire somewhere in the harness may be rubbed through and shorted to metal, a connector may have corrosion blocking the signal, or the sensor may be missing its supply voltage entirely. The ECM won't set this code off a single glitch — it watches the fault persist through specific driving conditions before turning on the Check Engine light. That freeze-frame data stored alongside P0122 shows engine load, RPM, coolant temperature, and vehicle speed at the moment the problem appeared, giving you a target when you need to reproduce the failure.

Common Symptoms of P0122

The vehicle enters limp-home mode, severely limiting engine power
Throttle response feels sluggish or disconnected from pedal input
Engine stalls when decelerating to a stop
Check Engine Light remains illuminated after the fault occurs
Idle speed becomes rough, fluctuating, or runs higher than normal

What Causes P0122

The most frequent culprit is a failed throttle position sensor itself — the internal circuitry gives out and drags the signal to ground. Beyond that, wiring problems rank second: a chafed wire rubbing against metal grounds the signal line, or a connector's pins corrode and create a high-resistance connection that collapses the voltage. Electronic throttle motor failures can also generate this code on some platforms since the throttle body and position sensor are integrated. Missing supply voltage to the sensor (often from a bad reference voltage) will keep the circuit low. Less commonly, a contaminated or failing MAF or MAP sensor creates intake metering faults that confuse the system and produce related codes alongside P0122. Faulty accelerator pedal position sensors can mimic this behavior too, especially on drive-by-wire systems.

How to Diagnose P0122

Hook up an OBD2 scanner and confirm P0122 is stored in permanent memory. Record the freeze-frame data — those exact conditions (load, RPM, temperature, speed) are what you need to replicate during your road test after repairs.
Scan for any other stored codes. P0122 frequently appears alongside fuel metering or intake-related codes, and those companions often point to the real root cause. Also pull up any technical service bulletins for your vehicle — manufacturers publish TSBs for known sensor and wiring issues that might match your symptom profile.
Get your hands on the wiring diagram and visually trace the throttle position sensor circuit. Check the harness along the engine firewall, near the intake, and around the throttle body itself. Look for cracked insulation, wires pinched by brackets, or heat damage from the exhaust. Wiggle the connector while monitoring live data — intermittent drops in the voltage signal indicate a loose or corroded terminal.
With the connector unplugged, measure reference voltage at the sensor side of the harness. If you're missing the expected 5-volt reference, the problem is upstream in the ECM or the wiring to it. Then check resistance from the signal wire to ground at the sensor connector — anything under a few ohms confirms a short-to-ground in the harness.
If the wiring checks out, remove the throttle body and inspect the plate and bore for carbon buildup that could affect movement. Clean with throttle body cleaner if needed, then verify the plate moves freely through its full range.
Reassemble, clear the code, and perform a complete drive cycle that covers the freeze-frame conditions. Watch the throttle position percentage in live data as you accelerate and decelerate — values should track smoothly with pedal movement. If P0122 returns, the sensor itself needs replacement.

Repair Options and Costs

If the throttle position sensor is simply faulty, replacing the sensor or the integrated throttle body assembly resolves the issue. For vehicles where the sensor is part of a complete throttle body unit, you'll be looking at assembly replacement rather than a standalone sensor. Here are typical parts-and-labor costs at independent shops in USD:

Replace MAF or MAP sensor (if identified as the root cause): $150–$400
Clean the throttle body: $80–$200
Replace the throttle body assembly: $250–$700

The overall range to fix P0122 typically falls between $80 and $700 depending on what component failed. Always confirm the diagnosis before replacing expensive assemblies — swapping the throttle body when the real issue is a $5 chafed wire wastes money and customer's time.

Driving Safety Verdict

P0122 carries a caution severity rating. Most vehicles respond to this fault by dropping into limp-home mode, which limits acceleration to roughly 30-40% of normal power. That mode exists to protect the engine and transmission, but it's not designed for highway merging or sustained high-speed driving. You can nurse the car to a repair facility on back roads, but if the throttle becomes unresponsive or the engine stalls completely, the vehicle should be transported from that point rather than driven further. Get the code diagnosed promptly — a small sensor or wiring issue left untreated can leave you stranded.