Understanding P0121 on the All-New 2024 Lexus RX
A P0121 code on your 2024 Lexus RX indicates the ECM has detected an abnormal pattern in the throttle position sensor data. The signal voltage is within bounds but doesn't correlate with your pedal input—a discrepancy that our detective recognizes as a sign that the throttle body communication needs investigation.
The 2024 RX rides on Toyota's all-new TNGA-K platform. The RX 350 uses a 2.4L turbocharged four-cylinder (T24A-FTS) with direct injection, while the RX 350h and RX 450h+ use hybrid powertrains with naturally aspirated engines and dual injection. The turbo RX 350's DI-only fuel system is more susceptible to carbon-related issues than the hybrid variants.
Symptoms to Watch For
- Check engine light on
- Hesitation during acceleration, especially the turbo model
- Idle smoothness degraded
- Throttle response feels delayed
- Possible reduced power delivery
Most Probable Causes
- ECM software calibration – The new platform may need a throttle mapping update. Lexus/Toyota regularly releases recalibrations for new generation vehicles. Likelihood: 35%
- Carbon buildup on throttle body – The 2.4L turbo DI engine is especially prone to carbon deposits. Even at low mileage, short-trip driving can cause rapid accumulation. Likelihood: 30%
- Throttle body manufacturing defect – New platform components may have occasional quality issues. Likelihood: 20%
- Connector or wiring issue – Factory assembly connector seating problem. Likelihood: 10%
- Intake system air leak – Loose turbo piping or intercooler connection (turbo models). Likelihood: 5%
Repair Costs
- All repairs: $0 under warranty
- Out-of-warranty reference: Cleaning $100–$180, replacement $400–$650, software update $100–$200
Dealer Service Is the Clear Choice
Your 2024 RX is covered under Lexus's 4-year/50,000-mile basic warranty and federal emissions warranty (8 years/80,000 miles). Take it to your Lexus dealer—all repairs will be performed at no cost. The dealer will use Techstream to diagnose the throttle system, apply any available software updates, and replace the throttle body if needed. Lexus dealers also provide loaner vehicles during service.
How AutoDetective AI Can Help
Upload your OBD-II scan data to AutoDetective for a preliminary diagnosis before your dealer appointment. Our AI identifies whether the 2.4L turbo or hybrid powertrain changes the likely cause ranking for your specific RX.