P0121 Code: Throttle Position Sensor/Switch Circuit Range/Performance

🟠 Moderate severity · drivable

Drivable, but the throttle reading is off, which can cause hesitation and poor idle.

What P0121 means

The throttle position sensor (TPS) is reporting a reading that doesn't match expected engine conditions. The TPS tells the computer how far the throttle is open so it can deliver the right amount of fuel.

Symptoms

Check engine light is on
Hesitation or surging under acceleration
Rough or unstable idle
Poor fuel economy

Common causes

most common: Faulty throttle position sensor
common: Worn or dirty throttle body
less common: Wiring or connector problem at the TPS

How to fix it

Fix	DIY?	Typical cost
Clean the throttle body	Yes	$10–40
Replace the throttle position sensor	Yes	$50–150
Repair TPS wiring or connector	Mechanic	$50–150

Frequently asked questions

Can I drive with a P0121 code?

Yes, but you may notice hesitation and rough idle. Fix it soon for smooth running.

What is the most common cause of P0121?

A faulty throttle position sensor. Cleaning the throttle body is a good first step before replacing it.

How much does it cost to fix a P0121?

Typically $50–$150 for a new throttle position sensor.

Related codes

P0122

P0122 Code: Throttle Position Sensor/Switch Circuit Low Input

P0123

P0123 Code: Throttle Position Sensor/Switch Circuit High Input

P0120

P0120 Code: Throttle Position Sensor Circuit

P0121 by vehicle brand

Causes and repair costs for P0121 differ between makes. Pick your brand for the specifics.

P0121 on a Mercedes-Benz

Volkswagen

P0121 on a Volkswagen

Updated 2026-08. This page is informational and not a substitute for professional diagnosis.