P0171 on Your 2023 Subaru Legacy
A P0171 code on your 2023 Subaru Legacy indicates a lean fuel condition on Bank 1. The 2023 Legacy offers a 2.5-liter flat-four boxer engine with 182 horsepower or a 2.4-liter turbocharged boxer making 260 horsepower. Bank 1 is the passenger side.
The ECU monitors the Bank 1 oxygen sensor and adjusts fuel trims. When the lean correction exceeds its programmed limits, P0171 is stored.
Symptoms
- Check engine light on
- Rough idle
- Hesitation on acceleration
- Reduced fuel economy
- Stalling at idle
- Hissing from engine bay
Common Causes
- Vacuum Leaks - Wide boxer intake layout has multiple potential leak points.
- MAF Sensor Contamination - Reduces airflow measurement accuracy.
- PCV System Failure - Creates unmetered air path.
- Boost Leak (Turbo Model) - Charge pipe connections can leak on the 2.4T.
Diagnosis
- Full code scan - Check for companion codes.
- Fuel trim analysis - Compare Bank 1 and Bank 2.
- Smoke or boost leak test - Find leaks.
- MAF and fuel pressure tests
- TSB check - Look for applicable bulletins.
Repair Costs
- Vacuum hose repair - $60 to $275
- Boost pipe repair (turbo) - $125 to $375
- MAF sensor replacement - $145 to $325
- Fuel pump replacement - $400 to $775
Diagnostic fee: $100 to $160.
Warranty
Your 2023 Legacy is under Subaru's warranty. Take it to a dealer for covered P0171 repair.
Prevention Tips
- Follow Subaru's maintenance schedule
- Replace air filters on time
- Use quality fuel
- Report performance changes to dealer
- Have software updates installed