P0121
Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance
Moderatesensor
Overview
The P0121 diagnostic trouble code means the PCM has identified a throttle/pedal position sensor/switch "a" circuit range/performance problem. This code indicates that a sensor or its circuit is not providing expected readings to the engine management system. Faulty sensor data can cause the PCM to make incorrect adjustments, affecting engine performance.
Symptoms
- Engine running rough
- Check Engine Light (MIL) illuminated
- Poor fuel economy
- Hard starting in certain conditions
Common Causes
- Faulty sensor (out of range or failed)
- Incorrect sensor installed
- Corroded or damaged sensor connector
- Poor ground connection for sensor
Diagnosis Steps
- 1Connect an OBD-II scanner and read all stored trouble codes and freeze frame data
- 2Locate the specific sensor referenced by the code
- 3Inspect the sensor connector for corrosion, damage, or loose pins
- 4Test the sensor output using a multimeter or scan tool live data
- 5Check the wiring between the sensor and the PCM for opens or shorts
Estimated Repair Cost
$75 — $350
Cost varies by vehicle, location, and repair shop. Includes parts and labor.
Commonly Affected Vehicles
Chevrolet CruzeHonda CivicNissan SentraKia Forte
Related Codes
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LowP0073Ambient Air Temperature Sensor Circuit High
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LowFrequently Asked Questions
Most automotive sensors last 80,000-150,000 miles, though this varies by sensor type and driving conditions. Oxygen sensors and temperature sensors tend to degrade gradually over time.