P0174: System Too Lean — Bank 2
What to do
As with P0171: driveable but worth attending to, since sustained lean running raises combustion temperatures. If both P0171 and P0174 are stored, say so — that pairing points at a shared cause rather than at anything bank-specific.
What this code means
The same lean condition as P0171, measured on bank 2. These two codes should always be read together, because whether they appear alone or as a pair is the most informative thing about them. P0174 on its own implicates that bank specifically — a leaking gasket on that side, injectors on that side, or that bank's oxygen sensor. P0171 and P0174 together implicate something both banks share, and in practice that most often means the mass air flow sensor under-reporting, a failed PCV system, or low fuel pressure starving both banks equally.
The same idle-versus-load fuel trim comparison described under P0171 applies here and is worth doing before any part is replaced.
Likely causes
Start here
- Vacuum leak in intake manifold or hoses · moderate
- Contaminated or failing mass air flow sensor · easy
- Failed PCV valve or hose · easy
- Low fuel pressure · moderate
- Split or disconnected intake boot · easy
Less common
- Clogged fuel injectors · moderate
- Leaking intake manifold gasket · moderate
- Exhaust leak before the sensor · moderate
- Restricted fuel filter · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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