Investigating P0121 on Your 2022 Acura MDX
A P0121 on your 2022 Acura MDX indicates the ECM has detected an irregular throttle position sensor signal. The voltage readings stay within expected limits, but the signal pattern doesn't correlate correctly with your accelerator pedal position. Our detective has found the first clue—the throttle body needs investigation.
The 2022 MDX launched on Honda's new light-truck platform with either a 3.5L V6 (J35Y6) with port fuel injection or the Type S's 3.0L twin-turbo V6 (J30A) with direct injection. The standard V6's port injection keeps the throttle body naturally cleaner, while the Type S's DI engine is more carbon-prone. Both use Honda's drive-by-wire throttle system.
Symptoms
- Check engine light on
- Hesitation during acceleration
- Idle roughness or fluctuation
- Throttle response feels delayed
- Possible reduction in power delivery smoothness
Most Likely Causes
- Carbon buildup on throttle body – PCV vapors coat the throttle plate. The Type S's DI engine is more susceptible, but the standard V6 can also accumulate deposits. Likelihood: 40%
- Throttle body assembly issue – Internal TPS or actuator motor wear in the electronic throttle body. Likelihood: 25%
- ECM software calibration – Honda/Acura releases updates for the new MDX platform's throttle management. Likelihood: 15%
- Wiring or connector fault – Corrosion or loose connection at the throttle body harness. Likelihood: 10%
- Intake air leak – Cracked intake boot or loose clamp (turbo piping on Type S). Likelihood: 10%
Estimated Repair Costs
- Throttle body cleaning: $100–$180 (shop) / $10–$25 (DIY)
- Throttle body replacement: $350–$600 parts and labor
- Wiring repair: $100–$250
- ECM update: $100–$200 (dealer)
Warranty & DIY Options
Your 2022 MDX should still be within Acura's 4-year/50,000-mile basic warranty depending on mileage. If covered, take it to the Acura dealer for free repair. If out of warranty, throttle body cleaning is a moderate DIY task. After cleaning, perform Honda's idle relearn: turn the key ON for 10 seconds without starting, then start the engine and idle for 10 minutes without touching the gas. Some owners also disconnect the battery for 20 minutes before starting the relearn.
How AutoDetective AI Can Help
AutoDetective's AI identifies whether your MDX's 3.5L V6 or 3.0L turbo V6 changes the diagnostic priority. Upload your scan data for a free, engine-specific diagnosis.