What Does P0121 Mean on a 2022 Subaru Impreza?
When your 2022 Subaru Impreza triggers a P0121 code, the ECM has caught the throttle position sensor (TPS) sending a signal that doesn't match expected patterns. The voltage stays within operational limits, but the behavior—how it tracks with your accelerator pedal—is inconsistent. Your Impreza's engine computer has detected a clue that the throttle system needs attention.
The 2022 Impreza runs Subaru's FB20 2.0L boxer engine with port fuel injection and standard Symmetrical AWD. The electronic throttle body houses the TPS internally, meaning the sensor isn't replaceable on its own. Port injection keeps the intake side cleaner than direct-injection engines, but 2-4 years of driving still generates enough carbon to cause issues.
Top Causes of P0121 on the 2022 Impreza
- Carbon buildup on throttle plate – The most common cause, even on port-injected boxers. Likelihood: 45%
- Throttle body assembly fault – Internal TPS electronics developing issues. Likelihood: 25%
- Connector or wiring problem – Corroded pins, loose fit, or damaged wiring. Likelihood: 15%
- ECM software calibration – A software update may resolve throttle mapping issues. Likelihood: 10%
- Intake air leak – Loose clamp or deteriorated boot near throttle body. Likelihood: 5%
Symptoms You May Notice
- Check Engine Light on
- Rough or fluctuating idle
- Hesitation when accelerating
- EyeSight warnings or deactivation
- Cruise control inoperative
- Mild fuel economy decrease
How Serious Is This Code?
P0121 is medium severity. Your 2022 Impreza will continue running, but expect degraded throttle response and possible EyeSight disruptions. Fix it soon—within 1-2 weeks.
Diagnostic Steps
- Scan for codes and review freeze frame data
- Visually inspect the throttle body for carbon deposits
- Monitor TPS voltage: ~0.5V idle, smooth sweep to ~4.5V WOT
- Check the throttle body connector for proper seating and clean pins
- Inspect wiring harness for damage or chafing
- Check for vacuum leaks in the intake system
Estimated Repair Costs
- Throttle body cleaning: $100–$200 (DIY: $10–$20)
- Throttle body replacement: $350–$600
- Wiring repair: $150–$300
- ECM software update: $100–$150 at dealer
Can You DIY This Fix?
DIY feasibility is moderate. The throttle body is accessible on the boxer engine. Clean with dedicated throttle body cleaner, then perform the idle relearn: key ON 10 seconds (no start), start engine, idle 10-15 minutes. Clear codes and test drive.
Check warranty coverage first—the 2022 Impreza may still be under the 3-year/36,000-mile basic warranty depending on purchase date and mileage. The 5-year/60,000-mile powertrain warranty is almost certainly active. If covered, let Subaru handle the repair at no cost.