System Too Lean (Bank 2)
The P0174 code means the vehicle's onboard diagnostic system has detected: System Too Lean (Bank 2). This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $0-$25 for vacuum line repair; $50-$150 for MAF sensor
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Common Symptoms
- Check Engine Light on
- Rough idle
- Hesitation or stumble under load
- Decreased fuel economy
Probable Causes (Ranked by Likelihood)
- Vacuum leak at Bank 2 intake or shared intake manifold Very High
- Dirty or failed MAF sensor (affects both banks) High
- Weak or clogged fuel injectors on Bank 2 Moderate
- Low fuel pressure Moderate
- Faulty Bank 2 upstream O2 sensor Moderate
Step-by-Step Diagnostic Procedure
-
Check LTFT on both Bank 1 and Bank 2. If both are high positive, the MAF sensor or a large shared vacuum leak is the cause.
-
If only Bank 2 LTFT is elevated, focus on Bank 2 specific vacuum lines and the intake manifold gasket on that side.
-
Clean the MAF sensor and retest. On V6 and V8 engines the MAF affects both banks equally.
-
Perform a smoke test or carburetor cleaner test targeting the Bank 2 intake runners.
-
Check fuel pressure and injector function on Bank 2 cylinders.
Common Fixes by Vehicle
What techs usually find when diagnosing P0174 on specific vehicles — tap your vehicle for the fix and the exact part:
2004-2014 Ford F-150 5.4L 3V moderate DIY
P0174 (Bank 2 lean) combined with P0171 (Bank 1 lean) almost always means a vacuum leak on the 5.4L. Check the intake manifold gaskets and the PCV hose on the passenger side valve cover. If only P0174, check the Bank 2 upstream O2 sensor (Motorcraft DY-1401). Cracked exhaust manifold on passenger side is also common.
Labor: 2-3 hours2006-2016 BMW 328i/X3 N52/N20 moderate DIY
Bank 2 lean on BMW inline-6 is typically the eccentric shaft sensor seal or the valve cover gasket leaking vacuum. The VANOS solenoid seals also harden and leak. Check for oil around the VANOS solenoids on top of the head. The CCV (crankcase vent) valve integrated into the valve cover is another common failure point.
Labor: 1.5-2 hours2009-2019 Dodge Ram 5.7L Hemi easy (MAF), hard (manifold) DIY
Check for a cracked exhaust manifold on the passenger side (Bank 2). The Hemi is famous for cracked manifolds causing false lean readings. Broken manifold bolts are equally common. If manifold is intact, clean the MAF sensor (Mopar 4606869AB) and check for vacuum leaks at the intake plenum gasket.
Labor: 10 min (MAF), 3-4 hours (manifold)2010-2020 Chevrolet Equinox/Traverse 3.6L easy (PCV), hard (gasket) DIY
Intake manifold gasket leak on the 3.6L V6. GM revised the gasket design. Also check the PCV valve in the rear valve cover. On higher mileage engines, the timing chain stretch can cause VVT issues that trigger lean codes. Scan for cam/crank correlation and check timing chain stretch with a scope.
Labor: 30 min (PCV), 3 hours (intake gasket)Frequently Asked Questions
Why do P0171 and P0174 appear together?
When both lean codes appear together, the cause is almost always a shared component: the MAF sensor or a large vacuum leak at the throttle body or intake manifold plenum that feeds both banks.
Which bank is Bank 2 on my vehicle?
Bank 2 is the side of the engine that does NOT contain cylinder 1. On most V8 and V6 engines, Bank 1 is the driver's side and Bank 2 is the passenger side: but this varies. Consult your vehicle's service manual to confirm.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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