What Does P0175 Mean on the 2022 Subaru Impreza?
The P0175 code on your 2022 Subaru Impreza indicates that bank 2 of the engine is running richer than the ECM's target 14.7:1 air-fuel ratio. The 2022 Impreza is equipped with the 2.0-liter FB20 boxer four-cylinder engine making 152 horsepower, paired with a Lineartronic CVT and Subaru's Symmetrical AWD. Bank 2 is the passenger side of the horizontally opposed engine, where the upstream O2 sensor monitors exhaust gas oxygen content and reports to the ECM for fuel trim adjustments.
Typical Symptoms
- Check engine light illuminated
- Fuel economy below the expected 28 city and 36 highway mpg
- Black exhaust smoke, especially under load
- Rough idle with noticeable vibration
- Strong fuel smell from the exhaust
- Hesitation or lag during acceleration
Boxer Engine Considerations
The Impreza's flat-four boxer engine has the same design characteristics found in all Subaru models. The horizontally opposed cylinder layout places the exhaust manifolds and O2 sensors in low, somewhat exposed positions compared to inline engines. For the 2022 Impreza, this means the bank 2 upstream O2 sensor on the passenger side can be affected by road spray, salt, and debris, particularly in winter driving conditions or on unpaved roads.
Primary Causes
1. Bank 2 Upstream O2 Sensor Failure
The upstream O2 sensor on bank 2 is the most common culprit behind P0175 on the Impreza. After a couple of years and 20,000 to 40,000 miles, the sensor can begin to respond slowly or develop a voltage bias. When the sensor signals incorrectly, the ECM over-fuels bank 2 to compensate for what it perceives as a lean condition. OEM Denso sensors provide the best calibration match for the Subaru ECM.
2. Fuel Injector Leak
The FB20 engine uses port fuel injection, and a leaking injector on bank 2 can add unmetered fuel to the combustion process. Carbon deposits on the injector tip or a worn internal seal prevent complete closure. This typically causes a rough idle and may trigger misfire codes alongside P0175.
3. Excessive Fuel Pressure
A fuel pressure regulator that fails to properly limit rail pressure causes all injectors to deliver more fuel per pulse than intended. Although this typically affects both banks, the bank 2 sensor may detect the enrichment first based on sensor sensitivity and ECM calibration. A simple fuel pressure gauge test can identify this problem.
4. MAF Sensor Contamination
The mass airflow sensor can be contaminated by oil vapors or by dust that bypasses a worn air filter. An underreading MAF causes the ECM to deliver more fuel relative to actual airflow. Cleaning with MAF-specific spray is the cheapest and easiest diagnostic step at under $15.
Diagnostic Steps
- Scan for all DTCs and record freeze frame data
- Review bank 2 STFT and LTFT values at idle and at 2,500 RPM
- Inspect the air intake system, including the filter, ductwork, and vacuum connections
- Clean the MAF sensor and clear codes, then drive to check for recurrence
- Monitor bank 2 upstream O2 sensor waveform for proper switching behavior
- Test fuel rail pressure with a mechanical gauge
- Conduct an injector balance or leak-down test if warranted
Repair Cost Estimates
MAF sensor cleaning: under $15. O2 sensor replacement: $150 to $350 including parts and labor. Injector cleaning: $100 to $200. Injector replacement: $250 to $600. Fuel pressure regulator: $180 to $400. The 2022 Impreza should still be within the 3-year/36,000-mile basic warranty, and emissions components like O2 sensors carry the federal 8-year/80,000-mile emissions warranty.
Is It Safe to Drive?
Yes, you can drive the Impreza with a P0175 code for normal daily errands. However, the rich condition wastes fuel, increases emissions, and can damage the catalytic converter over time. Since the 2022 model is likely still under warranty, schedule a dealer appointment soon to get it resolved at no cost to you.