P0171 on Nissan

The KA24DE engine in the 240SX is known for developing oil leaks from multiple locations as gaskets age. The rear main seal is the most problematic, leaking oil onto the clutch (manual trans) or flex plate (automatic). Valve cover gaskets also harden and leak, dripping oil onto the exhaust manifold. The oil pan gasket and front crank seal are additional common leak points. These leaks are exacerbated by age and the high operating temperatures of the KA24DE.

Repeated heat cycles — especially severe on the Twin Turbo, where the manifolds also carry the turbochargers — cause the Z32's exhaust manifold studs to stretch and snap, and the manifolds themselves to warp. Broken studs let the gasket blow out, producing the classic exhaust tick on cold start and acceleration, and on turbo cars the pre-turbine leak costs boost response. Extracting broken studs in the cramped bay (the passenger side is notoriously inaccessible) is labor-intensive, which is why so many cars are sold with studs already missing; RepairPal documents the warp-and-broken-stud pattern for the 300ZX with manifold replacement averaging about $1,190-$1,329.

The Z32 300ZX Twin Turbo fuel system components degrade with age, causing significant reliability issues. The fuel injectors become clogged or develop poor spray patterns, fuel dampers can leak, and the rubber fuel lines become brittle and crack. The extremely tight engine bay makes fuel line inspection difficult, and leaking fuel near hot turbo components creates a serious fire risk. The factory fuel lines use rubber hoses with spring clamps that weaken over time. This is considered the most critical maintenance item on the Z32TT.

The Z32 Twin Turbo has over 100 vacuum hoses that deteriorate with age, causing a cascade of problems including boost leaks, erratic idle, failed boost transitions, and check engine lights. The rubber hoses become hard and brittle after 25+ years, cracking and splitting. The complex vacuum system controls boost, EGR, HVAC, and fuel pressure regulation. A single cracked hose can cause multiple symptoms.

The revised VQ35DE "Rev-Up" engine (2005-2006 350Z, also known as the VQ35DE Rev-Up) is notorious for excessive oil consumption, often burning 1 quart every 1,000-2,000 miles. The issue is caused by defective galley gaskets (oil passage o-rings) that leak oil internally. The standard VQ35DE (2003-2004) and the later VQ35HR (2007-2009) do not suffer from this issue to the same degree. Nissan acknowledged the problem but did not issue a recall. The Rev-Up engine can be identified by its higher redline (7,000 vs 6,600 RPM).

P0174 references Bank 2, which physically exists only on the Altima's 3.5L VQ35DE V6 (the inline-4 has no Bank 2), so this code points specifically at the V6 rear cylinder bank. It nearly always appears together with P0171, and that pairing is the diagnostic tell: a lean condition on BOTH banks is caused by something common to the whole engine rather than one injector. On the VQ35DE the usual causes are shrunken/hardened intake manifold and plenum gaskets that develop vacuum leaks, a cracked PCV or intake hose, or a dirty MAF sensor under-reporting airflow to both banks. Nissan issued ECM-reprogram guidance (TSB NTB19-030) for lean-code complaints on 2016-2018 V6 Altima/Maxima where fuel trims are borderline, so a software update can be part of the fix after mechanical leaks are ruled out.

On the Altima's 2.5L QR25DE four-cylinder (and Bank 1 of the 3.5L V6), P0171 sets when the fuel-trim correction runs beyond about +25% because unmetered air is entering the engine downstream of the mass-air-flow (MAF) sensor. The two dominant Altima-specific culprits are (1) the flexible rubber intake air duct/boot between the MAF and throttle body, which grows brittle and splits at the accordion folds with age and underhood heat, and (2) hardened, shrunken intake manifold gaskets that let in a vacuum leak. A dirty or contaminated MAF sensor element that under-reports airflow is the third common trigger and is the cheapest to rule out. On the inline-4 there is only one bank, so P0171 appears alone; on the V6 it typically shows up paired with P0174 when the leak or MAF fault affects both banks.

A common first-gen Frontier issue is broken exhaust manifold studs, especially on the VG33E/VG33ER V6. Heat cycling warps the manifold and stresses the studs until one or more snap, creating a ticking exhaust leak that is loudest on cold start. Owners often mistake it for valvetrain noise, but the sound usually fades somewhat as the manifold heats up and expands.

The MR16DDT 1.6 DIG-T is a direct-injected engine, so fuel never washes the back of the intake valves. Combined with PCV oil vapor routed into the intake tract, hard carbon deposits accumulate on the valve stems and seats, typically becoming symptomatic between roughly 60,000 and 100,000 miles. Deposits disrupt airflow and prevent valves from sealing, producing cold-start rough idle, a shaking/shuddering idle that smooths out under load, hesitation and eventually stored misfire codes. Owners on Juke Forums repeatedly report chasing coils and injectors before finding the valves coked. The problem is aggravated by short-trip driving and extended oil-change intervals.

The VQ35DE 3.5L V6 in the 2016-2023 Maxima can develop excessive oil consumption, burning 1 quart every 1,500-3,000 miles. The issue is more prevalent in higher-mileage examples and is caused by piston ring wear and PCV system issues. Low oil levels can damage the catalytic converters.

The 2009-2014 Murano VQ35DE 3.5L V6 engine can consume excessive amounts of oil, sometimes 1 quart every 1,000-2,000 miles. The issue is caused by worn piston rings and valve stem seals. Nissan TSB NTB13-076 addresses the oil consumption test procedure. If the engine fails the consumption test, Nissan may authorize repairs under warranty.

The VG30E and VG33E exhaust manifolds warp slightly over years of heat cycling, which snaps the manifold-to-head studs (the rear stud on the passenger/right bank is the most common casualty). This creates an exhaust leak with a characteristic ticking/tapping that is loudest on a cold start and quiets as the engine warms and the manifold expands to close the gap. Nissan acknowledged the problem in a Technical Service Bulletin and released higher-strength replacement studs.

On 2022+ Rogues equipped with the 1.5L KR15DDT variable-compression turbo engine, owners have reported rough idle, oil odor, hesitation, and check-engine lights tied to crankcase ventilation or related air-fuel control issues. These complaints are distinct from outright transmission concerns and appear in owner forums and complaint databases as the newer engine accumulated mileage. In some cases, the issue presents as drivability problems without obvious external leaks.

On the B17-generation Sentra with the 1.8L MRA8DE four-cylinder, P0171 is overwhelmingly a vacuum/unmetered-air leak rather than a bad sensor. The intake manifold gasket becomes brittle with age and heat and lets in air the MAF never measured, driving long-term fuel trims positive until the ECM flags Bank 1 lean. The rubber air-intake boot between the MAF and throttle body also cracks and produces the same code. Less often a leaking brake-booster hose or PCV path contributes. Because the Sentra has only one physical cylinder bank, this is the true 'main' lean code on the car. Nissan TSB NTB19-022 provides a revised P0171 diagnosis for 2017-2019 Sentra that specifically warns against replacing the A/F sensor before ruling out unmetered-air leaks.

The KA24E engine in the Stanza develops oil leaks from the valve cover gasket, oil pan gasket, rear main seal, and front crank seal as the gasket materials age and harden. The most common and visible leak is from the valve cover gasket, which drips oil onto the exhaust manifold causing a burning oil smell. The rear main seal leak is more serious and labor-intensive to repair. These leaks are typical of aging KA24E engines across all Nissan applications.

First-generation (2000-2004) Xterras with the 3.3L VG33E/VG33ER V6 commonly crack the passenger-side (right) exhaust manifold over time due to heat cycling. A Nissan TSB acknowledged the issue. A cracked manifold produces a ticking/exhaust leak noise that is loudest on cold start, can trigger the check-engine light, and can affect downstream oxygen-sensor readings and performance.