P0122
UniversalThrottle/Pedal Position Sensor/Switch A Circuit Low Input
The engine computer monitors a signal from the throttle or accelerator-pedal position circuit labeled A. This code means the signal is lower than expected. The circuit helps the computer determine driver demand and manage engine response; the code identifies a detected electrical condition, not proof that a particular sensor needs replacement.
⚠️ Before You Begin (Safety First)
The vehicle may have reduced or unpredictable throttle response, or may stall. Stop driving if it cannot accelerate predictably, stalls in traffic, or responds unexpectedly; arrange a tow if needed.
Common Symptoms
- The check-engine light may be on because the engine computer has detected a low signal in the A circuit.
- Acceleration may be weak or delayed if the computer limits throttle response after detecting the fault.
- The engine may run roughly or stall if the fault disrupts engine control.
- The vehicle may enter a reduced-power mode, depending on its design and the fault.
- There may be no noticeable symptoms if the condition is intermittent or does not significantly affect engine control.
Common Causes
- A fault inside the throttle or accelerator-pedal position sensing component may produce a low signal.
- Damaged wiring, a poor connection, or corrosion may interrupt or alter the circuit signal.
- A short to ground, loss of a required supply or reference, or a ground-circuit problem may pull the signal low.
- A fault elsewhere in the monitored circuit or, less commonly, in the engine computer may cause the detected condition.
Diagnostic Steps
- Note when the warning light or symptoms occur, and check whether the vehicle has reduced or unpredictable throttle response. Do not continue driving if it is unsafe to control.
- With the vehicle safely parked and the ignition off, visually inspect accessible wiring and connectors for damage, looseness, or corrosion. Do not force connectors or probe terminals without the correct service information.
- Check for other stored diagnostic codes with a scan tool, and record them before clearing anything; related codes can help identify a shared circuit issue.
- If a suitable scan tool is available, review throttle and pedal position data for an implausible or intermittent reading. Interpret it using information for the exact vehicle.
- If the cause is not clear, have a qualified technician test the circuit and its supply, ground, and signal before replacing parts.
When to Call a Professional
Use a scan tool to review relevant throttle and pedal position data and check for related codes. A technician can test the circuit, connector, power or reference supply, ground, and signal using the vehicle-specific wiring information and procedures. Compare related signals only where the vehicle provides them.
Compare component listings
Confirm diagnosis and vehicle fitment before buying. A listing does not prove that a part needs replacement. We may earn a commission from qualifying purchases.
Commonly Asked Questions
Does P0122 prove that the throttle or pedal position sensor is bad?
No. It reports a low input in the A circuit. A sensor fault is one possibility, but wiring, connectors, supply, or ground problems can also cause the condition.
Can I keep driving with P0122?
Only if the vehicle responds predictably and can be driven safely. Reduced or erratic throttle response or stalling makes continued driving unsafe; stop and arrange assistance.
What does “low input” mean?
The engine computer is detecting a circuit signal below the expected range for its monitoring. The exact signal behavior and diagnostic procedure depend on the vehicle.
Should I replace the sensor first?
Not without diagnosis. Inspecting the circuit and checking scan data can help distinguish a sensor problem from a wiring, connector, supply, or ground fault.
Related Diagnostic Video
Browse Available Code Guides
Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.