P0171 on the 2024 Subaru WRX
A P0171 code on your 2024 Subaru WRX means the turbocharged boxer engine is running lean on Bank 1. The 2024 WRX uses a 2.4-liter turbocharged flat-four producing 271 horsepower. Bank 1 on the Subaru boxer is the passenger side.
As a performance car with a high-output turbo system, lean conditions need prompt attention. The ECU stores P0171 when Bank 1 fuel trim corrections can't compensate for the lean air-fuel ratio.
Symptoms
- Check engine light on
- Rough idle
- Reduced turbo performance and power
- Hesitation on acceleration
- Poor fuel economy
- Boost whistle or hissing noise
Common Causes
- Boost Leaks - Charge pipes, intercooler connections, and boost hose fittings can develop leaks. The most common cause on the WRX.
- MAF Sensor Contamination - Turbo oil mist coats the MAF element.
- Bypass Valve or Wastegate Issue - Allows pressurized air to escape.
- Fuel System Problems - High-pressure fuel pump or injector issues under boost.
Diagnosis
- Full code scan - Check for boost and knock codes.
- Fuel trim analysis - Lean at idle vs. under boost.
- Boost leak test - Pressurize the charge air system.
- MAF and fuel pressure tests
- Check for aftermarket modifications - Mods can cause lean codes.
Repair Costs
- Boost hose or clamp repair - $75 to $325
- MAF sensor replacement - $150 to $340
- Bypass valve replacement - $175 to $425
- High-pressure fuel pump - $575 to $1,050
Diagnostic fee: $120 to $175.
Warranty
Your 2024 WRX is under Subaru's 3-year/36,000-mile basic warranty and 5-year/60,000-mile powertrain warranty, provided the vehicle is unmodified. Aftermarket modifications may void warranty coverage for related components.
Prevention Tips
- Keep the WRX stock or ensure proper tuning for modifications
- Use recommended oil grade
- Replace air filter on schedule
- Use premium 93 octane fuel as required
- Check boost connections periodically