P0121 on the All-New 2024 Lexus GX
A P0121 on your 2024 Lexus GX indicates the ECM has detected an inconsistent throttle position sensor signal pattern. The voltage is within range but the behavior doesn't match expectations—our detective's investigation focuses on the electronic throttle body and its communication with the engine management system.
The 2024 GX is completely redesigned on Toyota's TNGA-F body-on-frame platform. It's powered by a 3.4L twin-turbo V6 (V35A-FTS) producing 349 hp, paired with a 10-speed automatic. This engine uses direct injection, making it more susceptible to carbon-related throttle issues compared to Toyota/Lexus engines with D-4S dual injection. An available hybrid variant adds electric assistance.
Symptoms on Your GX
- Check engine light illuminated
- Hesitation during acceleration, especially from low speed
- Idle may feel rougher than expected for a new Lexus
- Turbo response feels muted
- Possible reduced power message
Top Suspects
- ECM software calibration – First year on the new platform with the twin-turbo V6. Software refinements are expected and common. Likelihood: 40%
- Carbon deposits on throttle body – The 3.4L twin-turbo DI engine can accumulate carbon quickly, especially with short-trip or city driving. Likelihood: 25%
- Throttle body manufacturing defect – New platform components occasionally have quality issues. Likelihood: 20%
- Connector or wiring issue – Factory assembly connection problem. Likelihood: 10%
- Turbo system interaction – Twin-turbo boost pressure anomaly affecting throttle body readings. Likelihood: 5%
Repair Costs
- All repairs: $0 under warranty
- Out-of-warranty reference: Cleaning $100–$200, replacement $400–$700, software update $100–$200
Dealer Visit Required
Your 2024 GX is fully covered under Lexus's 4-year/50,000-mile basic warranty. As a first-year model on a new platform, the dealer may have specific Technical Service Bulletins already. Take it to your Lexus dealer—all diagnosis, software updates, and hardware replacement will be at no cost. Do not attempt DIY repairs on a vehicle this new.
How AutoDetective AI Can Help
The 2024 GX is a brand-new platform, and AutoDetective's AI is already tracking emerging patterns from early ownership reports. Upload your scan data for a preliminary diagnosis specific to the twin-turbo V6.