P0121 on Your 2024 Lexus NX: The Case File
A P0121 on your 2024 Lexus NX tells you the ECM has flagged an irregular throttle position sensor signal. The data falls within voltage limits but doesn't match the expected relationship with your accelerator pedal—our detective's instincts say the throttle body deserves closer inspection.
The 2024 NX continues on the TNGA-K platform with the NX 250/350 (2.5L four-cylinder with D-4S), NX 350h hybrid, and NX 450h+ plug-in hybrid. The NX 350 adds a 2.4L turbo-four with direct injection only. That turbo model is more susceptible to carbon-related throttle issues than the D-4S variants.
What You'll Experience
- Check engine light on
- Hesitation on acceleration (more noticeable on the turbo NX 350)
- Idle quality degraded
- Throttle may feel less responsive
- Possible reduced power delivery
Probable Causes
- ECM software update – Lexus regularly refines throttle and powertrain software across model years. Likelihood: 35%
- Carbon deposits on throttle body – The NX 350's 2.4L turbo DI engine is particularly prone. D-4S models accumulate deposits slower. Likelihood: 30%
- Throttle body component defect – Manufacturing quality issue with the TPS or actuator. Likelihood: 20%
- Connector or wiring issue – Loose factory connection or routing problem. Likelihood: 10%
- Turbo system interaction – Boost pressure anomaly affecting the throttle body (NX 350 turbo only). Likelihood: 5%
Cost to Fix
- All repairs: $0 under warranty
- Out-of-warranty reference: Cleaning $100–$180, replacement $350–$650, software $100–$200
Let Lexus Handle It
Your 2024 NX is fully covered under Lexus's 4-year/50,000-mile basic warranty. Take it to the dealer for a no-cost repair. Do not attempt DIY on a vehicle this new—warranty coverage makes the dealer the obvious choice. Lexus will use Techstream to diagnose, update software, and replace hardware as needed.
How AutoDetective AI Can Help
Upload your scan data to AutoDetective before your dealer appointment. Our AI will identify whether the turbo or hybrid powertrain in your NX changes the likely cause and give you a preview of the dealer's diagnosis.