P0174
System Too Lean (Bank 2)
Same condition as P0171 but on bank 2 of a multi-bank engine (V6, V8, flat-six, etc.). When P0171 and P0174 appear together, the cause is usually a shared component such as the MAF sensor or a central vacuum leak rather than a bank-specific fault.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
What we see in the workshop
ON FORD ECOBOOST
On V6 EcoBoost engines a lean bank 2 alongside P0171 points at a shared cause — usually a boost or vacuum leak rather than injectors on one bank.
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Common causes
Ordered by how often each turns out to be the cause.
- Central vacuum leak (intake manifold gasket, brake booster)Common
- MAF sensor contaminatedCommon
- Fuel pressure low (affects both banks)Possible
Parts involved
- Intake Manifold
- Mass Air Flow Sensor
- Fuel Pump
- Fuel Pressure Regulator
P0174 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.