# P0122: Throttle/Pedal Position Sensor/Switch "A" Circuit Low **Verdict:** Drive to a shop this week Air intake - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$900 - **Urgency:** This week - **Most likely:** Failed throttle sensor or wiring fault - **DIY?:** Steps 1-3 ## Quick answer P0122 means the engine computer is seeing a voltage from throttle position sensor "A" that is lower than the sensor should ever produce. That usually points to a failed sensor, a broken or shorted wire, or a bad connector rather than a dirty throttle. Many drive-by-wire cars go into reduced-power mode when it sets. ## What does P0122 mean? The throttle position sensor tells the engine computer how far the throttle plate is open. The computer sends it a steady 5-volt reference and a ground, and the sensor returns a signal voltage that rises as the throttle opens, typically from well under 1 volt at idle to around 4 volts or more at wide open. On most newer cars with electronic throttle, two sensors, "A" and "B", sit inside the throttle body and are checked against each other. P0122 is a circuit low code. It sets when the "A" signal drops below the lowest voltage a working sensor can make, often somewhere under about 0.2 to 0.3 volt depending on the maker, for more than a moment. That reading usually means an open signal or reference wire, a short to ground, or a failed sensor. Because the throttle affects safety, many cars set it on the first trip and limit power right away. ## What are the symptoms of P0122? - Check engine light on, often with a reduced-power or wrench light - Car accelerates weakly or will not rev past a low limit - Idle that is high, low or unsteady - Hesitation or stalling when you press or release the gas - Harsh, late or early shifts on some automatics ## What causes P0122? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed throttle position sensor "A"** (most common). The sensor itself can fail open inside, or its resistive track can wear through so the signal drops toward zero. Higher-mileage cars and older cable-throttle engines with a separate bolt-on sensor are most affected. If the signal reads near zero with the connector clean and the 5-volt reference present, the sensor is the likely fault. 2. **Open or shorted signal or reference wire** (common). A signal wire shorted to ground, or a 5-volt reference wire that is broken, leaves the computer reading almost no voltage. Harnesses near the throttle body can chafe on brackets or crack from engine movement and heat. Wiggling the harness while watching live data often makes the reading jump when you find the bad spot. 3. **Corroded or loose connector** (common). Water, heat and engine vibration attack the throttle body connector, and a pin that has backed out or turned green can stop the signal from reaching the computer. It often shows up after a car wash, heavy rain or recent engine work. Look for bent pins, a broken locking tab or green corrosion. 4. **Shorted 5-volt reference shared with another sensor** (less common). On many engines the throttle sensor shares its 5-volt reference with other sensors, such as the pedal or manifold pressure sensor. If one of those parts or its wiring shorts, it can pull the shared reference down. Several sensor codes setting at once, all reading low, are the clue that the short is elsewhere. 5. **Engine computer fault** (rare). An internal fault in the engine computer can stop it from supplying the reference voltage or reading the signal correctly. This is uncommon and is usually confirmed only after the sensor, wiring and connector all test good. Water damage or a past jump-start mistake raises the odds. Rule out simpler causes before replacing or reprogramming the computer. ## How do you diagnose P0122? 1. Read all stored codes; other throttle, pedal or sensor reference codes help narrow down where the fault is. 2. With the key on and engine off, watch throttle position "A" on a scan tool while slowly opening the throttle; it should rise smoothly from a small value. 3. Unplug the connector and check the pins for corrosion, then measure for about 5 volts on the reference wire and a good ground. 4. Check the signal wire for a short to ground or a break between the sensor and the engine computer. 5. If the circuit is good and the signal still reads low, replace the sensor or throttle body and run the throttle relearn. ## How do you fix P0122, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair wiring or connector | $100-$300 | Fixes a broken wire, a short to ground or a corroded terminal. | | Replace a separate throttle position sensor | $100-$300 | Applies to older cable-throttle engines with a bolt-on sensor. | | Replace the electronic throttle body | $300-$900 | On drive-by-wire cars the sensor is built in, so the whole unit is replaced and relearned. | ## Is it safe to drive with P0122? > **Drive to a shop this week.** You can usually drive carefully to a shop, but reduced-power mode can strike without warning and make merging or passing unsafe. If the car will not go above a crawl or stalls repeatedly, have it towed. ## Will P0122 fail an emissions test? P0122 keeps the check engine light on, which fails an OBD-II emissions test in most states. Throttle faults can also stop other monitors from running because the engine computer limits how the engine is driven. After the repair, clearing the code resets the readiness monitors, so drive several mixed trips before going for an inspection. ## After the repair: clearing P0122 After the repair, clear the code and run the throttle relearn if your car needs one; some reset by leaving the key on for a short period, others need a scan tool. Throttle position "A" should now sweep smoothly with no dropouts. A normal idle, full power and no returning code after several drives mean the fix worked. ## How to prevent P0122 - Keep the throttle body connector clipped tight and seated after any work near the intake. - Avoid aiming a pressure washer at the engine bay, especially at the throttle body connector. - Secure loose wiring harnesses so they cannot rub on brackets or touch hot engine parts. - Fix any sensor codes that set together early, since a shared reference short can spread. ## Codes often seen with P0122 - [P0121](/codes/p0121): Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance - [P0123](/codes/p0123): Throttle/Pedal Position Sensor/Switch "A" Circuit High - [P0505](/codes/p0505): Idle Air Control System - [P0507](/codes/p0507): Idle Air Control System RPM Higher Than Expected - [P0700](/codes/p0700): Transmission Control System (MIL Request) ## Frequently asked questions ### Can I drive with a P0122 code? You can usually drive a short distance to a shop, but be careful. Many cars limit power with P0122, which makes highway merging and passing risky. If the car barely accelerates, stalls or will not hold idle, have it towed rather than driving in traffic. ### What is the difference between P0121, P0122 and P0123? They describe different faults in the same sensor "A" circuit. P0122 means the signal is too low, often from an open wire or short to ground. P0123 means it is too high. P0121 means the voltage is in range but does not match what the computer expects from other readings. ### How much does it cost to fix P0122? Most P0122 repairs cost $100 to $900 at an independent shop. A wiring or connector repair runs about $100 to $300, as does a separate throttle sensor on older engines. Replacing a complete electronic throttle body costs about $300 to $900, depending on the car and part brand. ### Can a dirty throttle body cause P0122? Usually not, because P0122 is an electrical code about a voltage that is too low. Carbon buildup affects airflow and idle, which more often sets P0121 or idle codes. Cleaning the throttle body is still fine maintenance, but check the sensor, wiring and connector first for P0122. ### Can I fix P0122 myself? You can do the first steps yourself, such as checking the connector, looking for damaged wiring and reading live data with a scan tool. Replacing a bolt-on sensor or a throttle body is a moderate job on many cars. Some cars need a scan tool relearn afterward, so check the procedure first. ### What is reduced-power or limp mode? Reduced-power mode is a safety strategy where the engine computer limits throttle opening when it cannot trust the throttle sensors. The car may only reach low speeds or accelerate very slowly. It protects you from unexpected acceleration, and it clears once the fault is fixed and the code is cleared. ### Do I need to replace the whole throttle body for P0122? On most drive-by-wire cars, yes, because the throttle position sensors are built into the throttle body and are not sold separately. Older engines with a throttle cable often have a separate sensor held by two screws. Confirm the wiring is good first so you do not replace a working throttle body. ### Can a bad battery cause P0122? A weak battery or poor ground can cause odd sensor readings, but it rarely causes P0122 by itself. Low voltage during cranking can set several codes at once. If P0122 appeared with other random codes after a dead battery or jump-start, clear them, charge the battery and see what returns. ### Why does P0122 come and go? An intermittent P0122 usually points to a loose connector, a chafed wire or a worn spot on the sensor track. The fault appears only when the wire moves or the throttle passes that spot. Watching live data while wiggling the harness or slowly moving the throttle often reveals it. ### Does P0122 need a throttle relearn after repair? Many cars do need a relearn after a throttle body or sensor is replaced, so the computer learns the new closed position. Some do it on their own after a key-on wait, while others need a scan tool. Skipping it can cause a high or unstable idle and new idle codes. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other air intake codes - [P0112 Intake Air Temperature Sensor 1 Circuit Low (Bank 1)](https://diagxcar.com/codes/p0112) - [P0113 Intake Air Temperature Sensor 1 Circuit High (Bank 1)](https://diagxcar.com/codes/p0113) - [P0117 Engine Coolant Temperature Sensor 1 Circuit Low](https://diagxcar.com/codes/p0117) - [P0118 Engine Coolant Temperature Sensor 1 Circuit High](https://diagxcar.com/codes/p0118) - [P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0121) - [P0123 Throttle/Pedal Position Sensor/Switch "A" Circuit High](https://diagxcar.com/codes/p0123) - [P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control](https://diagxcar.com/codes/p0125) - [P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)](https://diagxcar.com/codes/p0128) - [P0130 O2 Sensor Circuit (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0130) - [P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0131) - [P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low](https://diagxcar.com/codes/p0107) - [P0405 Exhaust Gas Recirculation Sensor "A" Circuit Low](https://diagxcar.com/codes/p0405) ## Symptoms - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating) - [Why does my car jerk when I accelerate?](https://diagxcar.com/symptoms/car-jerks-when-accelerating) --- Source page: https://diagxcar.com/codes/p0122 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.