A P0122 code means the throttle or pedal position sensor “A” circuit reports a signal lower than the engine computer expects. The code is generic, so it applies to many makes, and the right fix depends on the cause.
The check engine light usually comes on, and the car may limit power. Most cases come from the sensor, its wiring or the pedal area, so start with a basic inspection.
What the P0122 Code Means
P0122 is the Throttle Position Sensor/Switch A Circuit Low Input code. It sets when the sensor output voltage falls below the range the engine computer expects.
According to KBB’s P0122 page, the code relates to the engine computer and the TPS circuit A output voltage. The sensor tells the computer how far the throttle or pedal is open, so a P0122 code means the computer is getting an unreliable picture of driver demand.
The official wording says “Sensor/Switch” because some vehicles use a pedal position switch instead of, or alongside, a sensor. Nearby codes describe other problems. The P0121 range and performance code is worded as a range or performance problem, and P0123 covers the high-input side of the same circuit, so read the exact code on your scan report before you choose a repair.
P0122 Symptoms You May Notice
The check engine light is often the first sign of a P0122 code. On some vehicles the engine computer enters failsafe mode, also called limp mode, which limits throttle opening to about 6 degrees or less, according to KBB.
Symptoms of a P0122 code vary by make and model. Some cars run for a long time with only the warning light, while others show power loss right away. Common complaints include:
- Check engine light on
- Reduced power and weak acceleration
- Hesitation, stalling or surging
- Rough, low or high idle, and a higher idle when stopped
- Hard starting
- Speed limits, depending on the make and model
KBB says most cars can usually be driven, but extended driving is discouraged, and severity varies by vehicle. Some cars show no symptoms for a long time, so a stored P0122 code is worth reading even when the car feels normal. Any stalling or acceleration problem needs prompt inspection, and a car that stalls repeatedly should not be driven in traffic.
Common Causes of a P0122 Code
P0122 usually comes from a faulty or incorrectly mounted throttle position sensor, damaged or shorted wiring, a faulty pedal sensor or switch, or debris blocking the pedal sensor. KBB and MechanicBase list the same core causes for a P0122 code.
Sensor and Wiring Faults
Frayed, damaged or shorted wiring is a listed cause, including a short to ground. A sensor that is broken, loose or incorrectly mounted can also set the code. MechanicBase adds a sensor that was not calibrated, and it lists an engine computer (PCM) problem as a possibility after the sensor and wiring are cleared.
Pedal and Floor Mat Problems
KBB lists debris from a floor mat blocking the pedal sensor. Check that the mat is secured and that nothing sits under the pedal before you test the wiring, because a simple obstruction is a cheap fix.
Throttle Sensor Voltage Reference
A normal throttle position signal uses a 5-volt reference and rises roughly linearly to about 4.6 volts at full pedal travel, according to KBB. Neither source gives other voltage thresholds, so use the factory specification for your vehicle when you compare readings.
| Reading point | Value in sources | Note |
|---|---|---|
| Reference voltage | 5 V on most vehicles | Per KBB |
| Full pedal travel | About 4.6 V | Output rises roughly linearly |
| P0122 condition | Signal below expected range | Per KBB and MechanicBase |
| Closed or idle position | Not given in sources | Use the factory specification |
Watch the live throttle position reading while you press the pedal slowly. A reading that never rises as the pedal moves points toward the circuit behind the P0122 code, but it is a clue to test, not proof of a failed part.
How to Diagnose P0122
Diagnose a P0122 code by scanning all modules, checking freeze frame data, and inspecting the sensor and wiring before replacing any part. KBB advises leaving the diagnosis to a qualified technician if you are not comfortable with the tests.
- Scan the engine computer and the TPS for codes, and write down P0122 and any other codes.
- Review the freeze frame data to see the conditions when the code was set.
- Compare the throttle position data with the factory specification in the service manual.
- Inspect the sensor for mounting problems, damage and poor connections, then check the wiring for shorts, especially to ground.
- Look for debris, such as a floor mat, that could block the pedal sensor.
- Clear the codes (see how to reset the check engine light) and retest to see whether P0122 returns.
- Calibrate the sensor with a suitable scan tool if the procedure requires it, and replace the sensor only if the wiring and mounting are sound.
- If the fault persists, MechanicBase suggests a PCM check, reprogramming or replacement as the last step.
Work with the engine off when you unplug connectors or probe wires, and keep the pedal and throttle linkage clear. Freeze frame data records the engine conditions at the moment the code set, so compare it with the service manual specifications before you decide on a part. Replace the sensor only if the tests point to it. Pinpoint tests follow the manufacturer’s procedure, so stop and call a technician if a wiring result is unclear.
What a P0122 Repair Can Cost
As of 2026-11-06, MechanicBase’s P0122 page estimates $100 to $350 to replace a throttle position sensor and $50 to $500 for a wiring short or damage. The page lists these ranges without a vehicle or labor breakdown, and it shows one update date for the whole page rather than a date for each estimate, so treat them as a rough guide, not a quote. Mounting the sensor correctly is the cheapest fix on the list at $25 to $75, which is why the inspection steps come before any replacement. For a fuller breakdown, see the guide to throttle position sensor replacement costs.
| Repair | Estimated range |
|---|---|
| Mount throttle position sensor | $25 to $75 |
| Repair electrical short or damaged wiring | $50 to $500 |
| Replace throttle position sensor or switch | $100 to $350 |
| Reprogram or replace PCM | $250 to $2,500 |
A PCM job for a P0122 code is the costliest case, and it usually comes last, after the sensor and wiring have been checked. Ask the shop to confirm the test results before you approve a part.
Throttle Sensor vs Pedal Sensor
The throttle position sensor measures throttle valve angle, while the pedal sensor measures how far the driver presses the accelerator in a drive-by-wire system.
According to Wikipedia’s throttle position sensor article, the sensor is usually fitted to the butterfly valve spindle, so it reads throttle position directly. That valve sits in the throttle body, so see throttle body repair costs if the whole assembly is suspect. The engine computer uses the sensor reading in a feedback loop to control the throttle.
Accelerator pedal sensors are related to the TPS and are used in drive-by-wire systems. A P0122 code can point to either part, which is why the freeze frame data and the wiring check matter before any replacement.
Frequently Asked Questions
Can I keep driving with a P0122 code?
Many cars with a P0122 code can be driven for a short time, but KBB says extended driving is discouraged. If the engine stalls, the throttle feels unresponsive or the car enters a limited power mode, arrange an inspection promptly instead of driving far.
Does P0122 always mean the throttle sensor failed?
No. KBB and MechanicBase both list wiring shorts, incorrect mounting, debris on the pedal and engine computer problems as causes of a P0122 code. Test the wiring and mounting before you buy a new sensor.
Can a floor mat cause P0122?
KBB lists debris from a floor mat blocking the pedal sensor as a possible cause. Make sure the mat is secured and nothing blocks the pedal, then clear the code and retest to see whether it returns.
Do I need a scan tool to read P0122?
A scan tool or OBD-II reader is the practical way to read a P0122 code and its freeze frame data, which shows the conditions when it was set. Both sources list reading and clearing codes as early diagnosis steps.
How is P0122 different from P0121?
P0122 is worded as a low input on the throttle or pedal sensor circuit, while P0121 is worded as a range or performance problem. Check the exact wording on your scan report, because it points the diagnosis in a different direction.
A P0122 code affects how the engine responds to your foot, so treat it as a safety issue rather than a cosmetic one. Have the wiring and sensor checked promptly, and ask the shop for the freeze frame data in its report.
