P0174 means bank 2 is running lean — too much air for the fuel being delivered — and it is diagnosed exactly the same way as its sibling, P0171. A vacuum leak on that side of the engine and a dirty or failing mass airflow sensor cause the large majority of cases. If you have both P0171 and P0174 together, the cause is almost certainly shared — the MAF sensor or fuel pressure — rather than a leak specific to one bank.
What Does P0174 Mean?
P0174 is System Too Lean (Bank 2) — identical in meaning to P0171, just reported by the oxygen sensor on the other bank. Only engines with two exhaust banks — V6, V8, and some flat/boxer layouts — can set this code; an inline engine only ever reports bank 1.
The mechanism is the same fuel-trim story as P0171: the ECU adds fuel to compensate for a lean mixture, and once that correction is pushed as far as it will go and the mixture is still lean, the code sets.
A leak specific to one side of the engine — a cracked hose feeding only that bank — produces one code alone. Both P0171 and P0174 appearing together point at something the whole engine shares: the mass airflow sensor, fuel pressure, or a large leak near the throttle body before the air splits between banks.
Common Symptoms
- Rough or hunting idle, often worst when the engine is cold.
- Hesitation on acceleration, especially pulling away.
- Misfires, since a very lean mixture is harder to ignite reliably.
- Poor fuel economy, despite the lean reading — the ECU is adding fuel to compensate, which costs more than the lean condition saves.
- A whistling or hissing sound from the engine bay if the leak is large.
Common Causes
The same list as P0171, applied to bank 2’s side of the engine — or shared components if both codes appear together:
- A vacuum leak on bank 2. A cracked hose, a loose clamp, or a failed intake gasket specific to that side.
- A dirty or failing mass airflow sensor. Affects both banks equally, which is why it is the prime suspect when both codes appear together.
- A weak fuel pump or clogged filter, starving both banks under load.
- A leaking PCV system or stuck-open purge valve, again affecting the whole engine.
- An exhaust leak before the bank 2 oxygen sensor, drawing in fresh air that the sensor misreads as a lean mixture.
- Dirty fuel injectors on bank 2 restricting fuel delivery to that side specifically.
How to Diagnose It
Follow the same process laid out in full in our P0171 guide:
- Read fuel trim at idle and at higher rpm. High at idle, better at speed points at a vacuum leak. High everywhere points at the MAF sensor or fuel delivery.
- Inspect intake hoses on bank 2’s side of the engine specifically if only P0174 is present.
- Clean or test the MAF sensor first if both P0171 and P0174 are stored together.
- Smoke test if the leak resists a visual and spray-test inspection.
Never work under a vehicle supported only by a jack. Use axle stands on firm, level ground, chock the wheels that stay down, and leave the car in gear or Park with the handbrake on. A jack lifts; stands hold.
Possible Fixes
| Cause | Fix | Typical cost |
|---|---|---|
| Vacuum leak, bank 2 | Replace the hose or gasket | $20 – $500 |
| Dirty MAF sensor | Clean with MAF-specific cleaner | $10 – $20 |
| Failed MAF sensor | Replace | $120 – $400 |
| Weak fuel pump | Replace | $400 – $900 |
| Dirty injectors, bank 2 | Professional clean | $100 – $250 |
Can I Drive With P0174?
For short trips, yes — the same guidance as P0171 applies. A lean mixture burns hotter ” than normal, which over time stresses exhaust valves and the catalytic converter. If misfires accompany it, ” “deal with it sooner rather than later, and watch for P0420 or its bank-2 twin appearing ” “afterwards as a sign the converter has already taken heat damage.
When to See a Mechanic
Book it in if the codes persist after checking the obvious hoses, and sooner if misfires or a check engine light accompany it. Mention whether P0171 is present alongside it — that single fact usually redirects the diagnosis toward a shared cause rather than a bank-specific leak. More in our trouble codes section.
Frequently Asked Questions
What is the difference between P0171 and P0174?
Only which bank reported it. P0171 is bank 1, P0174 is bank 2. Only V-shaped or flat engines with two exhaust banks can set P0174 — an inline engine only ever reports bank 1.
What causes P0174?
The same causes as P0171 on the other side of the engine: most often a vacuum leak or a dirty mass airflow sensor, followed by weak fuel delivery or a leaking PCV system.
Why do I have both P0171 and P0174 at the same time?
That combination points at something the whole engine shares rather than a leak on one side specifically — most often the mass airflow sensor or fuel pressure.
Can I drive with a P0174 code?
For short trips, yes. A lean mixture runs hotter than normal, which over time can stress the exhaust valves and catalytic converter, so it is worth fixing rather than ignoring long-term.
How much does it cost to fix P0174?
Often inexpensive — a vacuum hose is $20–$150, and cleaning the MAF sensor costs about $10. Costs rise if a fuel pump or injectors turn out to be the cause.
