What Does P0174 Mean on Your 2022 Subaru Impreza?
When your 2022 Subaru Impreza throws a P0174 code, it means the engine control module has detected that Bank 2 of your 2.0L horizontally-opposed (boxer) four-cylinder engine is running too lean. The air-to-fuel ratio has shifted too far toward the air side, and the ECM can no longer compensate with its fuel trim adjustments.
Symptoms You Might Notice
- Check engine light illuminated on the dashboard
- Rough idle that may smooth out as the engine warms up
- Sluggish acceleration or hesitation under load
- Decreased gas mileage compared to normal
- Intermittent stalling, particularly at low speeds
- A whistling or hissing noise from the engine compartment
Common Causes of P0174 on the 2022 Impreza
The 2022 Impreza shares the FB20 2.0L boxer engine with direct injection. Here are the most likely causes of a lean condition on Bank 2:
- Vacuum Leak — The flat-four layout uses longer intake runners that are prone to developing cracks or loose connections. Check around the intake manifold, throttle body, and PCV system.
- Dirty or Failing MAF Sensor — The mass airflow sensor sits in the intake tract and can become contaminated with oil or debris, leading to inaccurate readings.
- Low Fuel Pressure — A weakening fuel pump or a partially clogged fuel filter can cause insufficient fuel delivery to Bank 2.
- Exhaust Leak Before O2 Sensor — A cracked exhaust manifold or loose header connection on Bank 2 can introduce extra oxygen, fooling the O2 sensor into reading lean.
How to Diagnose the Problem
Here is a step-by-step approach to finding the root cause:
- Pull codes and check freeze frame data to see engine conditions when the code was stored.
- Monitor short-term and long-term fuel trims on Bank 2 with a scan tool. LTFT above +10% at idle indicates a lean problem.
- Perform a visual inspection of all vacuum hoses, connections, and the intake manifold gaskets.
- Use a smoke machine to detect hidden vacuum leaks.
- Clean the MAF sensor with dedicated MAF cleaner spray and recheck readings.
- Check fuel pressure at the fuel rail — it should be approximately 40-58 PSI.
Repair Options and Estimated Costs
- Vacuum hose or gasket repair: $80–$300. Most vacuum leaks are easy to fix once found.
- MAF sensor replacement: $120–$260. A straightforward DIY repair.
- Fuel pump replacement: $350–$650 with labor. Moderate DIY difficulty.
- Exhaust manifold gasket repair: $200–$450. Best left to a professional on the boxer engine.
Can You Still Drive?
A P0174 code is not immediately dangerous, but you should address it soon. Driving lean for extended periods increases exhaust temperatures, which can damage your catalytic converter — a repair that can cost $1,200 or more on the Impreza.
Prevention Tips
- Stay on top of scheduled maintenance, especially air filter and spark plug changes.
- Use Top Tier gasoline to keep injectors clean.
- Inspect intake boots and vacuum hoses during routine service.
- Address check engine lights promptly — small leaks turn into expensive repairs if ignored.
- Consider a fuel system cleaning service every 30,000 miles.