OBD codes / P0174 / Subaru Outback
P0174 on a Subaru Outback
System Too Lean (Bank 2)
EJ25 and FB25 2.5L boxer fours and the 3.6L H6
What P0174 usually means on a Outback
P0174 is the bank 2 counterpart of P0171 on the Outback: that bank is running persistently lean and the PCM is compensating with extra fuel. When P0174 appears alongside P0171, the cause is usually something that affects the whole engine, a dirty MAF, a big vacuum or PCV leak, or weak fuel supply, rather than a fault isolated to one bank. On the boxer layout bank 2 is simply the opposite side of the engine. A smoke test plus a MAF check is the efficient way to sort it.
Most likely causes on this model
- Shared vacuum or intake leak
A leak in a common intake area leans both banks and sets P0171 and P0174 together.
- Dirty or failing MAF sensor
A MAF under-reporting airflow leans the whole engine; clean or test it first.
- PCV system leak
A failing PCV path adds unmetered air affecting both banks.
- Weak fuel delivery
Low fuel pressure or dirty injectors starve both banks and show matching lean trims.
What it costs on a Outback
Because a bank 2 lean code usually shares a root cause with bank 1, the diagnosis and cost mirror P0171: a cheap MAF cleaning and a low-cost smoke test, with most fixes in the low hundreds. Only if fuel delivery is implicated does the bill climb toward a pump or injector repair. Treat matched P0171 and P0174 as one engine-wide problem rather than two separate ones.
Year, engine and mileage change the answer. Get a diagnosis for your Outback — it weighs these causes against your exact configuration and real complaint data.
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Subaru Outback problems & recalls by year
Based on widely reported patterns for this model; individual causes vary by year, engine and history. Generic P0174 behavior is covered on the main P0174 page. Confirm with a scan tool before buying parts.