P0121 on Your 2022 Lexus GX: What's Happening?
A P0121 code on your 2022 Lexus GX means the ECM has detected an abnormal throttle position sensor signal. The TPS voltage is within specs, but the signal pattern doesn't match expected behavior—our detective's evidence points to something interfering with the throttle body's normal operation.
The 2022 GX 460 is powered by the venerable 4.6L V8 (1UR-FE) with port fuel injection and a 6-speed automatic. This naturally aspirated, port-injected V8 is inherently less prone to carbon-related throttle issues than modern turbo DI engines. The GX's body-on-frame, off-road-capable design means the throttle body also deals with dust and environmental exposure.
Symptoms to Watch For
- Check engine light on
- Hesitation during acceleration, especially when loaded
- Idle may feel rough or unstable
- Throttle response slightly delayed
- Possible rough running at low speeds on trails
Causes Ranked by Probability
- Carbon buildup on throttle body – Even with port injection, PCV vapors deposit carbon over time. The GX's frequent use for towing and off-roading can accelerate deposits. Likelihood: 40%
- Throttle body assembly wear – At 3–4 years old with potentially high mileage, the integrated TPS and motor can develop wear. Likelihood: 25%
- Environmental contamination – Dust and debris from off-road use can infiltrate the throttle body area and affect TPS operation. Likelihood: 15%
- Wiring or connector degradation – Off-road vibration and environmental exposure stress wiring and connectors. Likelihood: 10%
- ECM software update – Toyota/Lexus calibration refinement for the 4.6L V8. Likelihood: 10%
Repair Costs
- Throttle body cleaning: $100–$180 (shop) / $10–$25 (DIY)
- Throttle body replacement: $300–$550 parts and labor
- Wiring repair: $100–$250
- ECM update: $100–$200 (dealer)
Warranty & DIY
Your 2022 GX may still be within Lexus's 4-year/50,000-mile basic warranty depending on mileage. Check your coverage before paying out of pocket. If out of warranty, throttle body cleaning is straightforward on the 4.6L V8—the throttle body sits atop the intake manifold with easy access. After cleaning, disconnect the battery for 30 minutes, reconnect, and idle for 10–15 minutes to complete the throttle relearn.
How AutoDetective AI Can Help
Upload your GX's scan data to AutoDetective for an AI analysis that factors in the 4.6L V8's port injection advantage and your driving conditions. Get a free diagnosis tailored to your specific vehicle.