P0174 — System Too Lean (Bank 2)
Moderate severityWhat it means
The mixture on bank 2 is too lean, so the engine control unit is adding maximum fuel correction. When P0171 and P0174 appear together on a V-type engine, the cause is almost always shared — a vacuum leak or a faulty MAF sensor rather than a bank-specific part.
Common symptoms
- Rough idle or hesitation
- Hard starting
- Lack of power under load
- Check engine light, often together with P0171
Likely causes
- Vacuum or intake leaks affecting both banks
- Dirty or faulty MAF sensor
- Weak fuel delivery (pump, filter, injectors)
- PCV or intake gasket leaks
- Exhaust leak before the oxygen sensor
What to check first
- If P0171 is also present, look for a shared cause first: intake leaks and the MAF sensor
- Compare fuel trims for both banks in live data
- Inspect vacuum hoses and the intake manifold gasket
- Test fuel pressure if needed
Can you keep driving?
Drivable in the short term, but lean running stresses the engine. Have it diagnosed soon.
Frequently asked questions
What is the most common cause of P0174?
The most likely cause is: Vacuum or intake leaks affecting both banks. Several other faults can set P0174 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P0174 and keep driving?
Clearing P0174 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P0174?
P0174 is a moderate-severity code. The car is often still drivable, but have it diagnosed soon — the underlying problem can get worse and it may fail an emissions test.
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