P0174 — System Too Lean (Bank 2)

What it means

Same lean condition as P0171 but on bank 2, the cylinder bank that does not contain cylinder 1, so the code only appears on V-type and boxer engines. Long-term fuel trim on that bank has run to its positive limit because there is more air in the mixture than the module expects. If P0171 is stored at the same time, the cause is common to both banks and usually lies before the intake manifold split or in the fuel supply.

Likely causes (most common first)

1. Unmetered air leak on the bank 2 side: cracked intake hose, leaking manifold gasket, brittle vacuum line
2. Faulty PCV system or a leaking brake booster hose feeding air into the intake
3. Contaminated mass air flow sensor underreporting the incoming air, which affects both banks
4. Low fuel pressure: weak fuel pump, clogged filter, faulty pressure regulator
5. Clogged injectors on bank 2 cylinders
6. Exhaust leak or a slow upstream oxygen sensor on bank 2 giving a false lean signal

Can you drive with it?

Short trips are possible, but a lean mixture raises combustion temperature and damages pistons and valves, so do not postpone the repair.