P0174 on Chevrolet

The 4.3L Vortec V6 uses a central port fuel injection system (nicknamed "spider" for its appearance) that is prone to leaking fuel internally into the intake manifold. The fuel pressure regulator and poppet nozzles develop leaks, causing hard starting, rough idle, and a fuel smell. This is a fire hazard.

Same intake gasket issue as all GM 4.3L vehicles. The composite gaskets fail, allowing coolant leaks. The Astro version is particularly problematic due to the engine positioned under the dash, making repairs more labor-intensive.

The 4.3L Vortec rarely fails head gaskets but very commonly fails its lower (plenum) intake manifold gaskets. The original-equipment gaskets use plastic/composite carriers that harden and shrink with heat cycling, typically leaking between roughly 100k-150k miles. Left unaddressed the leak can push coolant into the oil and eventually damage the bottom end.

Same as the S-10 truck - the 4.3L Vortec V6 develops intake manifold gasket leaks. The Blazer version is identical mechanically.

The early central port injection (CPI) system uses pressurized fuel lines under the upper intake manifold that develop cracks and leaks over time. Fuel leaks directly onto the hot engine, creating a serious fire hazard. The plastic fuel lines become brittle with age and heat exposure.

The 5.7L Vortec V8 (1996-1999) uses a Central Port Injection (CPI) spider assembly with poppet nozzles that clog and leak fuel. The plastic fuel lines become brittle and crack, causing hard starts, rough idle, and fuel odor.

Both the 2.2L OHV and 2.4L Twin Cam engines in the Cavalier are prone to head gasket failure. The 2.4L is particularly susceptible due to the aluminum head and iron block thermal expansion differences.

GM 3.1L V6 intake gaskets use a plastic carrier that warps and leaks coolant into the oil or externally. One of the most common failures on this engine across all GM platforms.

The 2.4L Ecotec engine uses low-tension piston rings that fail to maintain proper tension to keep oil in the crankcase. Vehicles consume 1 quart of oil per 800-1,000 miles. This defect can cause premature engine wear, engine failure, and potential fire risk if oil levels drop critically low. GM acknowledged this defect through TSBs and class action settlements.

A defective oil filter adapter can cause engine oil leaks that may contact hot exhaust components, creating a fire risk. Combined with the excessive oil consumption issue, low oil conditions can exacerbate the problem.

Vortec V8 intake manifold gaskets deteriorate causing coolant and oil leaks. Common on high-mileage vans, can lead to coolant contamination of oil if ignored.

The 3.4L and 3.8L V6 engines in 2000-2005 Impalas use Dex-Cool compatible intake manifold gaskets that deteriorate over time, causing coolant to leak externally or internally into the oil. External leaks appear as dried orange coolant trails on the engine block. Internal leaks contaminate the engine oil with coolant, turning it into a milky sludge that can destroy the engine bearings. This was one of the most widespread GM engine problems of the era and led to multiple class-action lawsuits.

The 3.1L and 3.4L pushrod V6 engines in the Lumina develop intake manifold gasket leaks, often attributed to Dex-Cool coolant reacting with the composite gaskets. Coolant leaks externally and can also enter the crankcase.

P0174 (lean, Bank 2) only sets on the V6 Malibus (3.5L LX9 in 2004-2007 and 3.6L LY7/LLT in 2008-2012), since the four-cylinder Malibus have only one bank. On these V6s the classic trigger is unmetered air reaching the cylinders on the bank opposite cylinder 1: a stuck-open or leaking EVAP purge solenoid (a widely reported GM 3.6L failure that drives both P0171 and P0174), a torn PCV/intake air hose, or an intake manifold gasket leaking vacuum to one bank. The ECM adds fuel to compensate, long-term fuel trims on Bank 2 climb past the +25% threshold, and the code sets.

The 3.8L Series II V6 develops intake manifold gasket leaks and the plastic coolant elbow on the front of the engine cracks. The supercharged SS models also have supercharger snout wear causing boost leaks.

The "spider" fuel injection system in the 4.3L Vortec V6 uses a central injector assembly with poppet nozzles connected by fuel lines. The poppet nozzles stick and leak, causing rough running, hard starting, and fuel smell. The original design was replaced by an updated MPFI system that uses actual injectors at each port.

The 4.3L Vortec V6 develops intake manifold gasket leaks that allow coolant to leak externally or mix with engine oil. The plastic gaskets deteriorate from heat cycling. This is a very common problem on all GM 4.3L V6 trucks.

Generation IV 5.3L Vortec engines burn an abnormal amount of oil — many owners report a quart or more every 1,000-2,000 miles. The defect is a combination of low-tension piston rings that fail to control oil, oil spray from the Active Fuel Management (AFM) system during cylinder deactivation, and a PCV path that draws oil mist into the intake. The oil fouls and prematurely wears spark plugs, causing rough idle, misfires, and a check-engine light. This was the subject of the Siqueiros v. GM class action (N.D. Cal., No. 3:16-cv-07244), which reached a final settlement in October 2025.

The Gen III LS truck engines use a plastic intake manifold with molded-bead gaskets. After many heat cycles the sealing beads flatten and crack, letting unmetered air in. Because the LS intake is 'dry,' the result is a vacuum leak that causes a lean condition, rough/unstable idle (worst on cold start), stumble, and lean/misfire codes rather than a coolant leak. Very common driveability complaint on high-mileage 4.8/5.3/6.0 trucks.

The Central Sequential/Port Fuel Injection ('spider') assembly used on Vortec 4.3L/5.0L/5.7L engines feeds nylon lines to poppet or MPFI nozzles inside the intake. Over time the poppet valves gum up and stick, O-rings and the pressure regulator leak, and the nylon lines crack. The result is misfires, hard starting, rough idle, a noticeable drop in fuel economy, and often a raw-fuel/rich condition. A leaking regulator can even flood a cylinder (hydrolock risk). Very high-demand failure on these older trucks.

The Gen III/IV LS-based Vortec V8s use a plastic (nylon) intake manifold with molded silicone/rubber gaskets. With heat cycling and age the gaskets harden and crack, creating an unmetered vacuum leak that leans out the mixture and can weep oil at the manifold-to-head sealing surface. Owners report rough/lean idle, hesitation, and lean-bank misfire codes. Not to be confused with the earlier 5.7 CSFI issue - this is the plastic-manifold sealing failure common across the GMT800 run.

The exhaust manifold-to-head bolts on GM small-block V8s fatigue and snap after years of heat cycling, most often the front and rear bolts on each manifold. The result is a distinctive tick/puff that is loudest on a cold start and quiets as the engine warms and the manifold expands to seal. It is extremely common on higher-mileage trucks and worse in road-salt regions where the bolt heads corrode. Left alone it causes an exhaust leak, can burn the manifold gasket, and may set O2/fuel-trim codes.

The 1996-2000 5.7L Vortec (L31) uses a Central Sequential Fuel Injection (CSFI) 'spider' assembly: one central housing feeds six nylon poppet spray nozzles via tubes. The poppet valves gum up with carbon and either stick open (raw fuel dumps, rich condition, hard hot/cold starting, fuel smell) or the plastic tubes crack/leak causing a lean misfire. This is one of the defining driveability failures of the GMT400 Tahoe. GM issued bulletin 87-65-07 and later covered many trucks under an extended emissions warranty for the poppet nozzles.

The 5.7L, 5.0L and 4.3L Vortec engines used a Central Sequential Fuel Injection (CSFI) "spider" assembly with nylon fuel tubes ending in spring-loaded poppet nozzles inside the intake. The poppets clog with carbon or leak/stick open, causing raw fuel intrusion, hard starting/flooding, and misfires. GM acknowledged the problem with special coverage 99066F on 1996-2003 CSFI systems (emissions-related, extending injector warranty to 10 years/200,000 miles for cleaning or replacement).

The 1996-1999 5.7L Vortec (L31) and 5.0L Vortec (L30) used a plastic-carrier composite lower intake manifold gasket that degrades and fails, typically between 60,000-120,000 miles. Failures commonly occur at the coolant ports and near the valley/distributor area, letting coolant seep externally, into the oil, or into the intake, and creating vacuum leaks. GM's light inch-pound torque spec contributed to uneven clamping and premature failure. This is one of the most widely reported problems on this generation truck.

Gen IV 5.3L V8s burn oil at an abnormal rate, frequently far worse than GM's own 1 qt / 2,000 mi 'acceptable' threshold. Three compounding root causes: (1) low-tension piston rings that fail to scrape oil from the cylinder walls; (2) the Active Fuel Management (AFM) oil-pressure relief valve in the valley that sprays a jet of oil directly at the deactivated cylinders' piston skirts, overloading the already-leaking rings; and (3) an early PCV routing in the valve cover that pulls liquid oil into the intake to be burned. Owners see the low-oil light between changes, fouled spark plugs on AFM cylinders (commonly cyl 1 and 7), and eventual carbon-clogged rings. Distinct from AFM lifter collapse — this is oil burning, not a lifter failure.

The small-displacement turbo engines in the Trailblazer can consume oil between changes, particularly the 1.2L 3-cylinder. Some owners report needing to add oil between the 7,500-mile change intervals.

The 3.5L and 3.9L V6 develop intake manifold gasket leaks, continuing the GM V6 gasket legacy. Coolant leaks externally or into engine oil.