P0174 on a Subaru

What is different about P0174 on a Subaru?

Subaru's side-by-side boxer layout makes an isolated P0174 a more physically distinct clue than it would be on a V6, since it points to an entirely separate side of the engine bay.

Patterns documented on Subaru vehicles

Side-specific intake and breather leaks: Because Subaru's boxer engine places bank 2 on a physically separate side of the vehicle from bank 1, an isolated P0174 points toward an intake gasket or crankcase breather leak specific to that side rather than a shared whole-intake cause.

Turbo plumbing asymmetry on some models: On some turbocharged Subaru layouts, intake and boost plumbing is not perfectly symmetrical between the two banks, meaning a boost-side leak can more plausibly affect one bank's lean reading without affecting the other.

What to check first on a Subaru

The order below narrows the generic P0174 list down to what is worth checking first on this make. It is a starting order, not a diagnosis: patterns are generation specific and a vehicle outside those generations may have none of them.

Check in this order

• Identify which physical side of the vehicle corresponds to bank 2 on the specific Subaru model
• Inspect intake manifold gaskets and breather hoses specific to that side
• On turbocharged models, check boost plumbing routed to that side
• Check whether P0171 is also present, suggesting a whole-intake cause instead

The generic picture behind P0174

This mirrors P0171 but for bank 2 of a V configured engine. Long term fuel trim on that bank has been pushed well beyond normal correction range trying to add fuel, indicating unmetered air or insufficient fuel delivery specific to that bank, or a shared intake issue affecting both banks.

Everything on the main P0174 page still applies here. This page narrows the cause list to the patterns documented on Subaru vehicles, it does not replace the underlying definition.

The generic version of this code

• P0174 on any vehicle