P0175 Code on the 2024 Subaru Impreza
Your 2024 Subaru Impreza has set a P0175 diagnostic trouble code, meaning the ECM has detected a rich air-fuel mixture on bank 2. The 2024 Impreza received a full redesign and now rides on the Subaru Global Platform, powered by the 2.5-liter FA25 boxer four-cylinder making 182 horsepower. This is an upgrade from the previous 2.0-liter engine. Bank 2 remains the passenger side of the horizontally opposed engine, where the upstream oxygen sensor monitors exhaust gases and reports to the ECM.
Symptoms to Watch For
- Check engine light on
- Fuel economy dropping below the expected 28 city and 36 highway mpg
- Black or dark exhaust emissions
- Rough or unsteady idle
- Fuel smell from the exhaust area
- Slight reduction in throttle response
New Platform, Same Boxer Considerations
While the 2024 Impreza is redesigned with a new platform and updated engine, it retains Subaru's signature horizontally opposed boxer layout. The FA25 engine positions O2 sensors and exhaust components in similarly exposed locations as previous generations. The new platform does offer improved underbody protection, but the bank 2 O2 sensor on the passenger side is still vulnerable to road spray, salt corrosion, and debris impact, particularly in harsh climates.
Common Causes
1. Defective Bank 2 O2 Sensor
Even on a brand-new vehicle, manufacturing defects or premature contamination can cause the bank 2 upstream O2 sensor to fail. Sensors contaminated by PCV system oil vapors or exposed to excessive moisture may read inaccurately, causing the ECM to add unnecessary fuel. Since the 2024 Impreza is under full warranty, this should be addressed at a Subaru dealer at no cost.
2. Fuel Injector Issue on Bank 2
The FA25 engine uses port fuel injection with precise injectors that must close completely between pulses. A manufacturing defect in an injector on bank 2 can allow fuel to drip into the intake port when it should not, creating a rich condition. This is uncommon on new vehicles but does occur.
3. Fuel Pressure Regulator Fault
If the fuel pressure regulator allows excessive rail pressure, all injectors deliver more fuel per cycle than intended. The bank 2 sensor may detect this enrichment before bank 1 triggers its own code. A fuel pressure gauge test at the rail test port identifies this issue definitively.
4. MAF Sensor Reading Error
The mass airflow sensor can be contaminated even on a new vehicle if the air filter is defective or improperly installed from the factory. A contaminated MAF underreads airflow, leading the ECM to calculate fuel delivery for less air than actually enters the engine. Cleaning with MAF-specific spray is the simplest first step.
Diagnostic Approach
- Have a Subaru dealer scan for all codes and review freeze frame data
- Check bank 2 fuel trims (STFT and LTFT) for excessive negative values
- Inspect the air intake system for proper assembly and any loose connections
- Clean the MAF sensor if contamination is suspected
- Monitor bank 2 upstream O2 sensor output for proper voltage switching
- Test fuel rail pressure against factory specifications
- Perform an injector leak-down test if other causes are eliminated
Warranty Coverage
The 2024 Impreza is fully covered under Subaru's 3-year/36,000-mile basic warranty and 5-year/60,000-mile powertrain warranty. Emissions components like O2 sensors also carry the federal 8-year/80,000-mile emissions warranty. All P0175-related repairs should be performed at your Subaru dealer under warranty at no cost. Do not attempt DIY repairs that could void warranty coverage.
Bottom Line
While it is frustrating to see a check engine light on a new vehicle, P0175 is a manageable issue with straightforward solutions. Take your 2024 Impreza to the dealer, let them diagnose and fix it under warranty, and continue enjoying your new car with peace of mind.