What Does P0121 Mean on a 2024 Subaru Impreza?
A P0121 code on your 2024 Subaru Impreza indicates the ECM has detected an abnormal voltage pattern from the throttle position sensor (TPS). The signal is present but doesn't behave as the computer expects given your driving conditions. On a new vehicle like this, P0121 is an unusual finding that should be investigated promptly at your Subaru dealer.
The 2024 Impreza is the first year of the sixth generation, built on an updated Subaru Global Platform. It features the FB20 2.0L boxer engine with port fuel injection and standard Symmetrical AWD. The electronic throttle body integrates the TPS internally. At near-zero mileage, carbon buildup is not a realistic cause—the investigation centers on factory and software issues.
Top Causes of P0121 on the 2024 Impreza
- ECM software calibration – New model year software may need a throttle control update. Likelihood: 35%
- Factory throttle body defect – Manufacturing issue with the integrated TPS. Likelihood: 30%
- Connector assembly issue – A plug not fully seated during factory assembly. Likelihood: 20%
- Electrical interference – Signal noise on the TPS circuit. Likelihood: 10%
- Carbon buildup – Extremely rare at low mileage. Likelihood: 5%
Symptoms You May Notice
- Check Engine Light illuminated
- Inconsistent idle speed
- Slight hesitation on acceleration
- EyeSight warnings or temporary deactivation
- Cruise control may not engage
How Serious Is This Code?
P0121 is medium severity. Your 2024 Impreza remains drivable, but any check engine code on a new vehicle deserves prompt attention. Address it soon—schedule a dealer visit within the week. EyeSight may be intermittently affected.
Diagnostic Steps
- Take the vehicle directly to your Subaru dealer—this is a warranty repair
- The dealer will use Subaru Select Monitor (SSM) to pull detailed diagnostics
- They'll check for applicable TSBs and software updates for the 2024 Impreza
- Throttle body connector and wiring will be inspected for factory assembly quality
- Live TPS data will be monitored for anomalies
- Throttle body replacement if a hardware defect is confirmed
Estimated Repair Costs
- Under warranty: $0 (fully covered)
- ECM reflash: $0 under warranty
- Throttle body replacement (if out of warranty): $350–$600
Should You DIY This?
DIY feasibility is low—your 2024 Impreza is fully covered under Subaru's 3-year/36,000-mile basic warranty and 5-year/60,000-mile powertrain warranty. Do not attempt repairs yourself, as this could jeopardize coverage. Let the dealer diagnose and fix it at no charge. Software updates require Subaru's proprietary SSM tool.