P0122 Code: Throttle Position Sensor/Switch A Circuit Low Input
Last reviewed May 2026 · Reviewed by the Find This Code Editorial Team
Quick Answer
The throttle position sensor is sending a voltage signal that's too low for what the ECU expects.
At a Glance
What this code means
The throttle position sensor (TPS) tells the ECU how far the accelerator pedal is being pressed, which controls fuel injection and ignition timing. P0122 means the voltage signal from the TPS circuit is below the minimum expected range. This can cause the ECU to misread throttle position, causing hesitation, stalling, or erratic behavior.
Common causes
- Faulty throttle position sensor
- Damaged, corroded, or shorted TPS wiring or connector
- Open circuit in the TPS signal wire
- Failed throttle body (less common — the TPS is often integrated)
- Poor ground connection at the TPS
Symptoms you might notice
- Hesitation during acceleration
- Rough idle or stalling
- Vehicle may not accelerate beyond a certain speed
- Limp mode on some vehicles
- Surging at steady throttle
Can you still drive?
With caution only. The vehicle may enter limp mode or behave unpredictably. Avoid driving until the issue is diagnosed.
How serious is this code?
Moderate to high. TPS issues can make the vehicle unsafe to drive if it's causing throttle control problems or limp mode.
Before you replace parts
Parts replacement is often not the first step. Before buying anything, it's worth checking these basics:
- Check for related codes — a companion code may point to the true root cause
- Inspect wiring, connectors, and grounds around the affected sensor or component
- Look for obvious physical damage: cracks, disconnected hoses, or corrosion
- Clear the code, drive the vehicle, and see if it returns — intermittent codes can come from loose connections
- Verify the part is actually faulty by testing it before replacing it
How to troubleshoot it
- Inspect the TPS wiring harness and connector for damage, corrosion, or loose pins
- Use a multimeter to check TPS reference voltage (typically 5V), ground, and signal voltage as the throttle is moved
- On drive-by-wire systems, check the throttle body and pedal position sensor wiring
- Clear the code and test-drive to see if symptoms match — intermittent wiring issues can be tricky to catch
- Replace the TPS if voltage readings are out of spec
Common mistakes to avoid
These are the most frequent diagnostic errors when dealing with P0122. Avoiding them can save time and money.
- Replacing the TPS without first checking the reference voltage and ground at the sensor connector
- Not performing a throttle position sweep test to confirm the sensor is producing a low signal
- Ignoring wiring harness damage along the TPS signal circuit that can cause intermittent codes
- Skipping the idle relearn procedure after sensor replacement
Tools that may help
These are the types of tools commonly used when diagnosing this code. Having the right tool can save time and help confirm a diagnosis before spending money on parts.
- Multimeter
- OBD-II scanner with live throttle position data
Estimated repair cost range
TPS replacement: $50–$200 for the sensor. On electronic throttle body systems, the entire throttle body assembly may need replacement: $150–$400.
Costs vary significantly by vehicle, location, and whether you use OEM or aftermarket parts. These are general ranges for reference only.
When to call a mechanic
If you've completed the basic troubleshooting steps and the code keeps returning, or if you don't have access to the proper diagnostic tools, it's worth consulting a professional. A qualified technician can perform a full diagnosis and confirm the root cause before any parts are purchased. When in doubt, get a professional opinion — it can save you from an expensive misdiagnosis.
Real-world note
On modern throttle-by-wire vehicles, the accelerator pedal and throttle body both have position sensors. P0122 may refer to either. Always check for related codes like P0221 (Throttle Position Sensor B) or P2135 (TPS correlation fault) alongside P0122.
Learn more
How we write these guides
Find This Code guides are written based on OBD-II specification documentation, established automotive diagnostic practices, and real-world patterns observed across vehicle makes and models. Content is reviewed for accuracy and plain-English clarity before publication. Pages are marked with a “Last reviewed” date and updated when diagnostic guidance or code interpretation changes. All content is educational — it is not a substitute for hands-on diagnosis by a qualified mechanic.
Last reviewed May 2026 · Find This Code Editorial Team · Editorial standards →
Sources & references
Our guides are written based on OBD-II specifications, automotive engineering principles, and established diagnostic best practices. Key reference sources include:
- U.S. EPA — On-Board Diagnostics (OBD)Official EPA documentation on OBD-II standards and emissions monitoring requirements for passenger vehicles.
- ASE — Automotive Service ExcellenceIndustry certification body for automotive technicians; sets best-practice diagnostic and repair standards.
Informational purposes only. This guide is for educational reference and is not a substitute for diagnosis by a qualified technician. Repair costs, causes, and symptoms may vary by vehicle make, model, year, and condition. Always consult a licensed mechanic before performing major repairs.