P0121 on a Lexus: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A Lexus with P0121 usually still drives, but the idle may be rough and throttle response sluggish until the issue is fixed.

What P0121 means on a Lexus

On a Lexus, P0121 means the throttle position sensor built into the electronic throttle body is reporting a reading the engine computer doesn't trust. Lexus uses drive-by-wire throttles, so the sensor is part of the throttle body assembly rather than a separate part.

Is P0121 common on Lexuss?

P0121 shows up on Lexus models like the ES, RX, GS, and NX, usually at higher mileage. A dirty throttle body is the most common cause, and cleaning it and letting the computer relearn the idle resolves many cases.

Commonly reported on: ES, RX, GS, NX.

Symptoms

Check engine light on
Rough idle or hesitation
Sluggish throttle response
Reduced power

Common causes

most common: Carbon buildup in the throttle body
common: Worn throttle position sensor
common: Faulty accelerator pedal position sensor
less common: Damaged throttle body wiring or connector

How to fix it

Fix	DIY?	Typical cost
Clean the throttle body and reset idle learning	Yes	$60–200
Inspect and repair the throttle wiring connector	Yes	$50–150
Replace the electronic throttle body assembly	Mechanic	$500–1000