P0121 - Throttle/Pedal Position Sensor/Switch A Range/Performance

P0121 is a throttle position, pedal position, or correlation fault. Confirm sensor sweep, circuit integrity, and throttle movement before replacing the throttle body.

Code first. Confirm symptoms and checks before pricing parts.

Code Overview

P0121 is a throttle position, pedal position, or correlation fault. Confirm sensor sweep, circuit integrity, and throttle movement before replacing the throttle body.

Common Causes

• Throttle position sensor or pedal position sensor signal dropout or disagreement
• Dirty, sticking, or carboned throttle plate
• Throttle body connector corrosion, loose terminals, poor 5V reference, ground, or signal circuit
• Damaged wiring near engine movement, prior repair disturbance, or water intrusion
• Throttle body motor or internal sensor failure after circuit and mechanical checks
• PCM or relearn issue only after voltage, ground, and command checks pass

Symptoms

• Reduced power or limp mode
• High or unstable idle
• Poor throttle response
• Stalling
• Check engine light

Diagnostic Steps

1. Check for limp mode, reduced power message, and related APP/TPS correlation codes
2. Inspect throttle body bore, plate movement, connector, terminal tension, and harness routing
3. Graph TPS and APP signals while slowly sweeping the pedal and throttle command
4. Verify 5V reference, ground, and signal circuits before replacing the throttle body
5. Clean throttle deposits only when allowed by service information, then perform relearn if required
6. Confirm repair with stable idle, smooth pedal sweep data, and no reduced-power return

Repair Difficulty

Moderate

General difficulty estimate for the most common repair path.

Likely Repairs & Cost Guides

Confirm the repair path before pricing parts.

Related OBD Codes

Browse nearby codes when systems overlap.

Next Steps

Move from code to checks, then estimate.