P0171 on the 2024 Subaru Impreza
A P0171 code on your 2024 Subaru Impreza indicates a lean condition on Bank 1. The redesigned 2024 Impreza features a 2.5-liter flat-four boxer engine producing 182 horsepower. Bank 1 on Subaru's boxer is the passenger side.
The ECU stores P0171 when the Bank 1 oxygen sensor detects persistent lean operation that exceeds the fuel trim correction limits.
Symptoms
- Check engine light on
- Rough idle
- Acceleration hesitation
- Reduced fuel economy
- Possible stalling
- Hissing from engine bay
Common Causes
- Vacuum Leaks - Even on new vehicles, a loose factory clamp or defective hose can cause a vacuum leak on the boxer intake.
- MAF Sensor Issue - Contamination or malfunction.
- PCV System Problem - Failed valve or cracked hose.
- Software Calibration - ECU may need a software update for refined fuel management.
Diagnosis
- Full code scan with freeze frame
- Fuel trim analysis - Bank comparison.
- Smoke test - Find vacuum leaks.
- MAF sensor and fuel pressure tests
- TSB and software update check
Repair Costs
- Vacuum hose repair - $60 to $250
- MAF sensor replacement - $140 to $310
- PCV valve replacement - $50 to $165
- ECU software update - $0 to $150 (often free under warranty)
Diagnostic fee: $90 to $150.
Warranty
Your 2024 Impreza is under Subaru's 3-year/36,000-mile basic warranty and 5-year/60,000-mile powertrain warranty. Take it to a dealer for no-cost repair.
Prevention Tips
- Follow Subaru's maintenance schedule
- Replace air filter on time
- Use quality fuel
- Report performance changes to dealer promptly
- Allow dealer to install software updates