Decoding P0121 on Your 2022 Lexus NX
When your 2022 Lexus NX triggers a P0121, the ECM has detected that the throttle position sensor signal is behaving unpredictably within its normal voltage range. The detective in your engine computer has noticed that the TPS data doesn't match the expected pattern—something is disrupting the smooth communication between your pedal input and the throttle plate position.
The 2022 NX launched on Toyota's all-new TNGA-K platform. The NX 250 and NX 350 use a 2.5L naturally aspirated four-cylinder with D-4S dual injection, while the NX 350h is a hybrid. The NX 450h+ is a plug-in hybrid. The 2.5L engine's dual injection system helps keep the throttle body cleaner than DI-only setups.
Symptoms
- Check engine light on
- Hesitation during acceleration
- Idle roughness beyond normal NX smoothness
- Throttle response may feel delayed
- Possible subtle power delivery inconsistency
Most Likely Causes
- Carbon buildup on throttle body – Despite D-4S, PCV vapors still coat the throttle plate over time. City driving accelerates this process. Likelihood: 40%
- Throttle body assembly issue – Internal TPS or actuator motor degradation. Likelihood: 25%
- ECM software update needed – As a first-year model on the new platform, software refinements are expected. Likelihood: 20%
- Wiring or connector problem – Corrosion or loose pin in the throttle body connector. Likelihood: 10%
- Intake air leak – Loose clamp or cracked intake boot. Likelihood: 5%
Repair Costs
- Throttle body cleaning: $100–$180 (shop) / $10–$25 (DIY)
- Throttle body replacement: $350–$600 parts and labor
- Wiring repair: $100–$250
- ECM software update: $100–$200 (dealer)
Warranty Coverage
Your 2022 NX should still be within Lexus's 4-year/50,000-mile basic warranty depending on mileage. If covered, take it to the Lexus dealer for free diagnosis and repair. If out of warranty, throttle body cleaning is a moderate DIY task—the NX's compact engine bay is tighter than some models, but the throttle body is accessible from the top. After cleaning, disconnect the battery for 30 minutes, then idle for 10–15 minutes to complete the relearn.
How AutoDetective AI Can Help
AutoDetective's AI analyzes your 2022 NX's specific powertrain variant and mileage to identify the most probable cause. Upload your scan data for a free diagnosis tailored to your vehicle.