OBD-II Car P0174 Error
What it means
P0174 means the engine computer has detected that the air-fuel mixture on Bank 2 is 'too lean' — there is too much air and not enough fuel. Bank 2 is the cylinder group opposite cylinder #1, so this code appears on V-shaped, W-shaped, or flat engines with two banks. The computer figures this out from the long-term fuel trim: when it has to keep adding fuel to compensate but still cannot reach the correct mixture, it sets P0174. Common symptoms are rough or unstable idle, hesitation or reduced power on acceleration, engine knocking or pinging, harder starting, and a check engine light. It often appears together with P0171 (the Bank 1 lean code), which usually points to a shared cause like a vacuum leak or a dirty mass airflow sensor.
The bottom line on the P0174 error
P0174 says Bank 2 is running lean, and the usual culprit is unmetered air sneaking in — a cracked vacuum or PCV hose or a dirty MAF sensor — far more often than a failing fuel pump. Because it commonly sets alongside P0171, look for one shared leak on both banks before replacing bank-specific parts.
Start with the cheapest checks: inspect the intake hoses and clean the MAF sensor cheaply. Do not let a lean condition linger — the extra heat can damage the catalytic converter, so pay for a shop smoke test if you cannot find the leak.
P0174 snapshot
Our own at-a-glance triage of the P0174 error, from the verified data on this page. See error-code rankings → · How we score →
Common causes of the P0174 error
- Vacuum leak — cracked intake hoses, a torn intake boot, or a leaking gasket letting in unmetered air
- Dirty or failing mass airflow (MAF) sensor under-reporting incoming air
- Weak fuel pump or clogged fuel filter reducing fuel pressure and volume
- Clogged or leaking fuel injectors on Bank 2
- Failing fuel pressure regulator
- Faulty or aged oxygen sensor feeding bad data to the engine computer
- Exhaust leak ahead of the upstream O2 sensor pulling in extra air
Which OBD-II cars get the P0174 error
P0174 only appears on engines with two cylinder banks — V6, V8, V10, W, and flat/boxer layouts — so you will not see it on an inline four-cylinder. It is very common on Ford V6/V8 engines (notably the 4.6L/5.4L Triton and EcoBoost V6, where cracked plastic intake parts and PCV hoses leak air), and shows up on GM, Toyota/Lexus, and many European V6/V8 engines as they age. Because it shares causes with the Bank 1 lean code, P0174 frequently sets alongside P0171.
How to fix the OBD-II Car P0174 error
- 1Check fuel trim and look for an obvious vacuum leakUse a scan tool to read long-term fuel trim. If both Bank 1 and Bank 2 read high positive numbers, suspect a shared vacuum leak. Inspect intake hoses, the intake boot after the MAF, the PCV system, and gaskets for cracks. Spraying a small amount of carb cleaner near suspected joints and listening for an idle change can help locate a leak (do this carefully, away from hot or sparking parts).
- 2Clean or test the MAF sensorA dirty MAF sensor commonly causes lean codes. Remove it and clean the sensing element with dedicated MAF cleaner (never touch it). If cleaning does not help and live data shows incorrect airflow, the sensor may need replacement.
- 3Check fuel deliveryTest fuel pressure against the manufacturer spec. Low pressure points to a weak pump, clogged filter, or failing regulator. Consider a fuel injector cleaning or test if pressure is fine but the lean condition persists on Bank 2 only.
- 4Inspect for exhaust leaks and verify O2 sensorsAn exhaust leak before the upstream sensor can fool the computer into adding too much fuel correction. Check the manifold and pipe joints, and confirm the upstream O2 sensor is switching normally in live data before condemning fuel or air parts.
🧰 When to call a professional
Call a professional if you cannot find the vacuum leak, lack a scan tool to read fuel trims and live sensor data, or if the code returns after cleaning the MAF and checking fuel pressure. A persistent lean condition is worth fixing promptly because the extra heat from running lean can damage pistons, valves, and the catalytic converter.
OBD-II P0174 vs OBD-II P0171 vs OBD-II P0300: how they compare
How this code stacks up against related error codes for difficulty, urgency, and cost.
| OBD-II P0174 | OBD-II P0171 | OBD-II P0300 | |
|---|---|---|---|
| DIY difficulty (1–5) | 3 | 3 | 3 |
| Urgency (1–5) | 3 | 3 | 4 |
| Typical cost | $$ | $$ | $$ |
How much does it cost to fix the P0174 error?
| DIY parts only | $20–$300 |
| Professional diagnosis & repair | $100–$500 |
| If major component (fuel pump) | $1,000–$1,700 |
Repair or replace?
P0174 is usually a moderate, affordable fix when the cause is a vacuum leak (a cracked hose, PCV part, or intake gasket, often under $50–$300) or a dirty MAF sensor that can be cleaned for the price of a can of MAF cleaner. Because it commonly appears with P0171, look for one shared cause on both banks before replacing bank-specific parts. DIY is reasonable for hose, PCV, and MAF work; pay a shop ($75–$150 diagnosis, often including a smoke test) when you cannot locate the leak or fuel pressure is out of spec — a failing fuel pump can run $1,000–$1,700 installed. Prices vary widely by model and region, so treat these as general ranges. Do not let a lean condition linger: it runs the engine hotter and can trigger misfires that damage the catalytic converter over time.
Common replacement parts for the P0174 error
| Vacuum / PCV hose | $10–$50 | Most common and cheapest fix; brittle plastic PCV lines are a frequent culprit | |
| MAF sensor | $150–$400 | Clean first (nearly free); replace only if still out of spec | |
| Intake manifold gasket | $100–$400 | Common single-bank leak point on aging V6/V8 engines | |
| Fuel pump | $1,000–$1,700 | If low fuel pressure is confirmed as the cause; prices vary by model |
Prices are typical retail ranges and vary by model and supplier — always confirm the exact part number for your appliance before buying.
OBD-II P0174 error — FAQ
＋ − Is it safe to drive with this code?
You can usually drive short distances to a shop, but do not ignore it. A lean mixture raises combustion temperatures and, if severe or left unaddressed, can damage internal engine parts and the catalytic converter over time. Avoid hard acceleration while the code is active, and get it diagnosed soon.
＋ − How much does it cost to fix?
It depends entirely on the cause. Fixing a vacuum leak or cleaning the MAF can be very cheap (sometimes under $100). A new MAF sensor or oxygen sensor typically runs $150–$400 installed, while fuel pump or injector work can climb to $400–$1,000 or more. Start with the cheapest likely causes first.
＋ − Why do I have P0174 and P0171 at the same time?
P0174 is the lean code for Bank 2 and P0171 is the lean code for Bank 1. When both appear together, the cause is usually something shared by the whole engine — most often a vacuum leak, a dirty MAF sensor, or low fuel pressure — rather than a problem isolated to one bank.
Sources & manufacturer references
This guide is independently written and not affiliated with OBD-II. Always unplug appliances before servicing and follow your model's manual. Error codes and steps can vary by model — when in doubt, consult a qualified technician.