System Too Lean (Bank 2)
In short
P0174 means the engine is running lean on Bank 2 — too much air relative to fuel — and the computer has run out of room adding fuel to compensate. It's the Bank 2 twin of P0171 and only appears on V6/V8 engines. When P0171 and P0174 appear together, the cause is almost always something that affects both banks at once: a dirty MAF sensor, low fuel pressure, or a large vacuum/PCV leak. A leak on just one bank trips P0174 alone.
Is it safe to drive with P0174?
Generally safe in the short term — the car runs, though you may feel a rough idle or hesitation. A lean mixture burns hotter and can lead to misfires, detonation, and accelerated wear over time, so diagnose it soon, especially if misfire codes appear alongside it.
Symptoms
- Check engine light on
- Rough or surging idle, sometimes stalling
- Hesitation or stumble on light acceleration
- Slightly reduced power
- Often no obvious symptom besides the light
Common causes (most → least likely)
How to diagnose it (before buying parts)
- 1 Read live fuel-trim data. High positive Short- and Long-Term Fuel Trims on Bank 2 (e.g. +15% to +25%) confirm the lean condition. Compare to Bank 1: if both are lean, suspect a shared cause (MAF, fuel pressure); if only Bank 2 is lean, hunt a leak on that bank.
- 2 Note when the lean trim is worst — at idle points to a vacuum leak; at higher RPM/load points to the MAF or fuel delivery.
- 3 Clean the MAF sensor with MAF-specific cleaner and recheck; a contaminated MAF is the classic cause of dual-bank lean codes.
- 4 Smoke-test or spray carb cleaner around the intake, PCV, and Bank 2 runners to find unmetered air.
- 5 If idle vacuum and MAF check out, test fuel pressure under load to rule out weak fuel delivery.
Repair options & cost
By manufacturer
P0171 + P0174 together is extremely common on 4.6/5.4 V8s and EcoBoost engines, usually a dirty MAF or a torn PCV/intake hose. Check the rubber intake elbow and PCV first.
Cracked intake manifold gaskets and PCV faults are common dual-bank lean sources on older V6/V8s.
Dirty MAF or brittle vacuum lines on V6s; clean the MAF and inspect the PCV hose before replacing parts.
VQ V6 intake gaskets and MAF sensors are known culprits; verify with fuel trims and check both banks.
Frequently asked questions
What's the difference between P0171 and P0174?
Same lean condition on different cylinder banks — P0171 is Bank 1, P0174 is Bank 2. You only see P0174 on V-configuration engines. When both codes are present, look for a shared cause like a dirty MAF or low fuel pressure rather than two separate leaks.
Can I drive with P0174?
Short-term, usually yes, but a lean mixture runs hot and can cause misfires and long-term wear. Diagnose it soon — sooner if you also have misfire codes.
Will cleaning the MAF fix P0174?
Often, when both banks read lean. A MAF coated in dirt or oil reads low and leans out the whole engine. Clean it with MAF-specific spray and recheck fuel trims; if Bank 2 is still lean, look for a vacuum leak on that side.
Why only Bank 2 and not Bank 1?
A lean code on just one bank usually means unmetered air is entering that bank specifically — a cracked vacuum line, intake gasket, or runner leak on the Bank 2 side — rather than a shared problem like the MAF or fuel pump.
Related codes
Sources and model caveats
Code behavior and repair procedures can vary by engine, model year and calibration. Confirm the diagnosis against the vehicle's service information before replacing parts.
- Manufacturer service information
- Field diagnostic experience — replace with cited, verifiable references before publishing