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P0122: Throttle/Pedal Position Sensor/Switch A Circuit Low Input

Quick Answer

Not safe to drive

P0122 means the ECU is seeing an abnormally low voltage on throttle position sensor circuit A, typically under 0.2V when it expects 0.5V to 4.5V. Most cars drop into limp mode with capped throttle.

Severity
Moderate · Electrical

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What does P0122 mean?

P0122 is a electrical-related diagnostic trouble code classified as moderate severity.

Where it is on the car

  1. Air filter box
  2. Mass airflow sensor (MAF)
  3. Throttle body and throttle position sensor
  4. Intake manifold and MAP sensor
  5. Engine (cylinder head)

What are the symptoms of P0122?

  • Check Engine Light on, often paired with a throttle or EPC warning
  • Reduced engine power (limp mode): the ECU limits throttle opening or engine speed, and how hard it limits varies by manufacturer
  • Rough or hunting idle between 500 and 1500 rpm
  • No response or long delay when pressing the accelerator
  • Stalling at idle or when coming to a stop
  • Slight decrease in fuel economy from open-loop fueling
  • Transmission holding gears longer or shifting harshly because it has no load signal

What causes P0122?

  • Faulty throttle position sensor or worn contacts inside the throttle body

    : high

  • Corroded, loose, or backed-out connector at the throttle body

    : high

  • Broken or chafed signal wire between TPS and ECU

    : medium

  • Open or shorted 5V reference wire from the ECU

    : medium

  • Bad ground on the TPS circuit

    : low

  • Failed ECU (rare, diagnose last)

    : low

Is it safe to drive with P0122?

No - address this immediately. The ECU usually forces the car into limp mode with reduced power and a locked idle. You can limp home, but hard acceleration and highway merging become risky.

How do you diagnose P0122?

  1. Read all stored codes and note companion codes such as P0222 or P2135, or other low-input codes such as P0107 that point to a shared 5V reference
  2. Watch live data for TPS1 voltage with key on, engine off. Below 0.2V confirms the low input
  3. Wiggle the throttle body connector and harness while watching live data to catch intermittent faults
  4. Backprobe the TPS signal, 5V reference, and ground pins with a multimeter. Reference should read 4.9 to 5.1V
  5. If reference and ground are good but signal stays near 0V, replace the TPS or throttle body
  6. If the 5V reference is missing, check the wiring back to the ECU for a short to ground
  7. After repair, clear codes and run the throttle body relearn per the manufacturer procedure (on some makes this needs manufacturer-level software)
  8. Road test and confirm TPS voltage sweeps smoothly from ~0.5V at closed throttle to ~4.5V at WOT

How much does P0122 cost to fix?

Repair Parts Cost Labor Cost Total Estimate DIY Difficulty
Clean and reseat throttle body connector €0–€10 €0–€40 €0–€50 Easy
Replace standalone throttle position sensor €30–€120 €40–€90 €70–€210 Easy
Replace electronic throttle body assembly €180–€550 €80–€180 €260–€730 Moderate
Repair damaged wiring or connector pins €10–€40 €60–€180 €70–€220 Moderate
ECU diagnosis and replacement (worst case) €400–€1200 €100–€250 €500–€1450 Professional

Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.

P0122 on specific vehicles

Volkswagen

Volkswagen Golf

2005-2015 (Mk5/Mk6, 1.4 TSI CAVA/CAXA and 2.0 TDI CBEA/CJAA)

The EPC light comes on with P0122 on these Golfs. On 1.4 TSI engines the throttle body actuator motor brushes wear on higher-mileage cars. A replacement throttle body needs a basic-settings adaptation with manufacturer-level software.

P0122 on Ford

Ford F-150

See Ford-specific causes & cost

Toyota

Toyota Camry

2007-2017 (2.5L 2AR-FE and 3.5L 2GR-FE)

The TPS is integrated into the throttle body (Toyota part 22030-0H030 range) and not sold separately. Toyota's service procedure requires an idle air volume learn after replacement or battery disconnect.

BMW

BMW 3-Series

2006-2013 (N52, N54, N55)

BMW uses dual redundant TPS in both the pedal and throttle actuator. P0122 usually pairs with P2135 and drops the car into a restrictive failsafe. Water leaks into the E-box under the cowl are a well-documented cause on E90s.

P0122 on Honda

Honda Civic

See Honda-specific causes & cost

Common questions about P0122

Can I just drive with P0122 until the weekend?
You can move the car short distances, but limp mode caps power and makes merging or overtaking dangerous. Fix it before any highway driving.
Will disconnecting the battery clear P0122 for good?
It'll clear the light, but if the sensor or wiring is faulty the code returns within minutes of driving. You're masking the problem, not fixing it.
Do I need a throttle relearn after replacing the throttle body?
Yes, on almost every drive-by-wire vehicle. Without the relearn the idle will hunt or stall. On some makes it is a key-on and idle procedure; on others the throttle adaptation must be run with manufacturer-level software that supports it. A generic OBD2 code reader cannot run it.
Why did P0122 appear right after I cleaned my throttle body?
The connector probably wasn't fully seated, or carb cleaner seeped into the TPS. Reseat the plug and let it dry overnight before condemning parts.
Can a weak battery or bad alternator trigger P0122?
Yes. If system voltage drops below about 10V during cranking or under load, the 5V reference can sag and log a low-input code. Load-test the battery before chasing sensors.

Read our detailed guides

Sources

  1. ricksfreeautorepairadvice.com ricksfreeautorepairadvice.com/idle-relearn-procedure-honda/

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