P0121

Throttle/Pedal Position Sensor "A" Circuit Range/Performance

OBD-II diagnostic trouble code P0121indicates a fault detected by the vehicle's onboard computer. This code applies to all OBD-II compliant vehicles and should be addressed promptly to avoid potential engine or emissions system damage.

Severity Level 3 — Moderate

This code indicates a moderate issue that may affect vehicle performance and fuel economy. Continued driving is possible in most cases, but prompt diagnosis and repair are recommended to prevent further damage.

Common Symptoms

• Check Engine Light on
• Erratic or unresponsive throttle
• Engine may enter limp mode (reduced power, max ~30 mph)
• Sudden RPM changes without pedal input
• Vehicle may not accelerate when pressing the gas pedal

Possible Causes

• Faulty throttle position sensor (TPS) — internal wear on the resistive track causes dead spots
• Carbon buildup in throttle body preventing proper throttle plate movement
• Damaged wiring or loose connector at throttle body
• Faulty accelerator pedal position sensor (drive-by-wire vehicles) — separate from TPS
• Faulty electronic throttle body assembly — internal motor or sensor failure

Common Fixes

• Clean throttle body to remove carbon buildup ($50-200 shop, $10-20 DIY with spray cleaner)
• Replace throttle position sensor (TPS) ($40-200 parts, may require throttle body relearn procedure)
• Replace complete electronic throttle body assembly ($300-800 including labor and relearn)
• Repair damaged wiring or connector ($50-200)
• Perform throttle body idle relearn procedure ($0-100 diagnostic fee)

Estimated Repair Cost

These are estimated costs based on generic repair data. Actual costs may vary depending on your vehicle, location, and labor rates.

Explore Repair Costs

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