What Does P0174 Mean on Your 2024 Subaru Impreza?
Your 2024 Subaru Impreza uses the updated 2.0L direct-injection boxer engine, and a P0174 code means the powertrain control module has detected an excessively lean air-fuel mixture on Bank 2. The system has exceeded its ability to add fuel to correct the imbalance, so it sets this diagnostic trouble code.
Symptoms You Might Notice
- Check engine light on or flashing
- Engine idles roughly or unevenly
- Lack of power during acceleration
- Worse fuel economy than expected
- Engine may surge or hunt at idle
- Possible hissing noise from under the hood
Common Causes of P0174 on the 2024 Impreza
Even though the 2024 Impreza is relatively new, several issues can trigger a lean code on Bank 2:
- Vacuum Leak — A loose clamp, cracked hose, or improperly seated intake gasket can let unmetered air into the engine. This is the number one cause on boxer engines.
- MAF Sensor Contamination — Oil mist or debris on the mass airflow sensor leads to incorrect air measurement, causing the ECM to under-fuel.
- Fuel Delivery Issue — A fuel pump that is not meeting specification or a kinked fuel line can starve Bank 2 of adequate fuel.
- Faulty O2 Sensor on Bank 2 — A sluggish or biased oxygen sensor can report false lean readings, causing the ECM to set P0174 even when the mixture is correct.
How to Diagnose the Problem
- Read all stored and pending codes. Note if P0171 (Bank 1 lean) is also present — if so, the issue is likely upstream of both banks.
- Check live fuel trim data. Long-term fuel trim above +15% on Bank 2 confirms a real lean condition.
- Visually inspect all vacuum hoses, the PCV valve, and intake manifold connections.
- Use a smoke test to find hidden vacuum leaks.
- Test fuel pressure — the 2024 Impreza should read around 43-58 PSI at idle.
- Inspect the MAF sensor element and clean if contaminated.
Repair Options and Estimated Costs
- Vacuum leak repair: $80–$280. Often a simple hose or clamp replacement.
- MAF sensor cleaning or replacement: $20–$270. Cleaning is a quick DIY job.
- Fuel pump replacement: $400–$700. Usually requires professional installation.
- O2 sensor replacement: $150–$350. Moderate DIY difficulty on the boxer engine.
Can You Still Drive?
A steady check engine light with P0174 allows short-distance driving, but a flashing light means stop immediately — that indicates misfires. Get the lean condition diagnosed within a few days to avoid catalytic converter damage.
Prevention Tips
- Follow Subaru's recommended maintenance schedule for air filters and spark plugs.
- Use Top Tier gasoline to minimize fuel system deposits.
- Inspect vacuum hoses and intake connections at each service interval.
- Do not use aftermarket air intake systems without proper tuning — they can introduce metering errors.
- Address any check engine light promptly to avoid secondary damage.