2024 Subaru P0171: What It Means & Is It Safe to Drive?
P0171 on the 2024 Subaru: System Too Lean (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
What this code means
The engine is getting too much air relative to fuel. The O2 sensor sees excess oxygen in the exhaust and the PCM is adding more fuel than normal to compensate.
Common causes on the 2024 Subaru
- Dirty or faulty mass airflow (MAF) sensor
- Vacuum leaks (PCV hose, intake gasket, brake booster)
- Weak fuel pump or clogged fuel filter
- Leaking or stuck open fuel injectors (less common)
Symptoms
- Check Engine Light
- Rough idle, hesitation, lack of power
- Possible spark knock under load
- Poor fuel economy
Typical fixes
- Clean or replace MAF sensor
- Locate and seal vacuum leaks
- Replace fuel filter / test fuel pressure
- Smoke test intake system
Repair cost range
For a 2024 Subaru, repairs for P0171 typically fall between $50 and $500, depending on the root cause and labor rates in your area.
Known issues on Subaru
Subaru P0171 on naturally-aspirated EJ25 2.5L engines often traces to a failing MAF sensor—the Subaru MAF degrades gradually and the car can run for years with a slightly degraded reading. Clean the MAF first, then compare short-term and long-term fuel trims. On turbocharged Forester XT and WRX (EJ255/EJ257), a cracked turbo inlet hose between the MAF and turbo compressor inlet is the most common cause—the rubber boot cracks at the clamped ends. On EZ36 3.6L, the MAF housing itself can develop hairline cracks.
Most commonly affected models