P0300 on Chevrolet

Gen IV 5.3L AFM engines burn oil at an abnormal rate — many owners report consuming roughly a quart every 1,000-2,000 miles with no external leak. The accepted root cause is a combination of GM's low-tension piston rings plus the AFM system spraying oil onto the cylinder walls during cylinder deactivation; oil gets past the rings and is burned in the combustion chamber. The PCV system and carboned-up rings compound it. The chronic low oil level then accelerates the AFM lifter failures these engines are also known for. This was the subject of a high-profile class-action (Sloan v. GM / Siqueiros) covering Gen IV 5.3L AFM trucks, and it is one of the most-searched Silverado complaints.

The 5.3L (and 6.2L) V8 with Active Fuel Management — GM's cylinder-deactivation system that drops the engine to 4 cylinders to save fuel — is notorious for collapsed AFM lifters. The special deactivating lifters (and the lifter oil-manifold/VLOM that feeds them) fail when oil pressure/timing to the lifter is compromised, causing the lifter roller to seize. A collapsed lifter no longer opens its valve, producing a dead-cylinder misfire, a loud ticking/tapping, rough idle and major power loss. If driven on, a collapsed lifter can wipe the camshaft lobe and destroy the cam, turning a lifter job into a top-end rebuild. This is consistently ranked the #1 Silverado engine problem and generates heavy forum and search traffic across the entire 2007-2019 AFM era. Disabling AFM (range tuner/AFM delete) is the common owner mitigation.

GM's Active Fuel Management (AFM) system deactivates cylinders to improve fuel economy, but can cause premature lifter wear and failure. Symptoms include rough idle, misfires, and valve train noise. GM released updated lifters.

The EcoTec3 5.3L V8 (L83, and later L84 with Dynamic Fuel Management) uses Active Fuel Management to deactivate cylinders 1, 4, 6, and 7 under light load. The AFM lifters that collapse to deactivate those cylinders are prone to sticking or mechanical failure, often during a mistimed cylinder-mode switch event. A failed lifter stops actuating its valve, producing a loud ticking/tapping noise, rough idle, a flashing check-engine light, and a single-cylinder misfire (cylinder 7 is the most commonly reported). If a lifter disintegrates it can wipe the camshaft lobe, turning a lifter job into a cam-and-lifter job. Owners on CarComplaints report this surfacing anywhere from 80,000-120,000 miles, and it is the subject of multiple GM lifter/AFM lemon-law and class-action discussions.

The turbocharged 2.7L inline-4 (RPO L3B, marketed as TurboMax) used in fourth-gen Silverado 1500 work-grade and mid-trim trucks has generated a growing body of owner complaints distinct from the better-known 5.3L/6.2L V8 problems. Reported failures include collapsed/failed valve lifters (some at very low mileage — one documented 2022 Silverado Custom failed at ~22k miles), heavy carbon accumulation on the direct-injection intake valves causing rough idle, hesitation and 'chugging' under load, sticking PCV valves, and elevated oil consumption (owners report roughly a quart every 1,000-1,500 miles). Because the 2.7L is heavier-loaded in the full-size Silverado than in the Colorado/Canyon, it spends more time under boost and heat, which owners and shops link to accelerated valvetrain and turbo wear. GM issued repair campaigns in 2024 touching L3B/L2R engines.

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.

Bosch fuel injectors on early Duramax engines develop internal leaks causing rough running, white smoke, and hard starts. LB7 generation (2001-2004) most affected with class action settlement history.

The fuel injector wiring harness on the Duramax diesel routes across the top of the engine under the valve covers. The harness rubs against the valve cover and rocker arms, causing the insulation to wear through and the wires to short or open. When an injector wire is damaged, the affected cylinder misfires, the engine runs rough, and white smoke pours from the exhaust. The chafing is accelerated by engine vibration and can affect multiple cylinders over time. GM released updated harness routing clips but the fundamental design has the harness in a high-wear location.

The 1.8L is prone to ignition coil (cassette-style coil pack) and spark plug degradation that causes random and single-cylinder misfires, rough idle, and hesitation. A frequent aggravating factor is oil pooling in the spark plug wells/tubes from a leaking valve cover gasket, which fouls the plugs/coils and re-triggers misfires until the gasket is addressed. This valve-cover-gasket-into-spark-plug-tube leak is a well-documented failure pattern on this engine.

The 1.4L engine in the Spark is prone to premature ignition coil failure, often causing misfires and rough running. Individual coil packs fail due to heat soak in the tight engine bay. Spark plugs also wear faster than the recommended interval suggests.

GMT400-era Vortec V8s use a Central Sequential Fuel Injection (CSFI) 'spider' assembly with poppet-valve nozzles inside the intake. The poppet valves clog with carbon or the nozzle seats fail, so they leak/dribble fuel instead of atomizing. This causes hard starting, misfires, rough idle, hesitation, poor fuel economy, and often a raw-gasoline smell; failing poppets can dump fuel into a cylinder. A very high-demand repair for high-mileage 1996-2000 Suburbans.

The Active Fuel Management (AFM) and Dynamic Fuel Management (DFM) systems on the 5.3L and 6.2L V8 engines deactivate cylinders to save fuel by collapsing hydraulic valve lifters. These lifters have a complex locking pin mechanism that fails, causing the lifter to collapse and the affected cylinder to misfire. A collapsed lifter can also damage the camshaft lobe it rides on, turning a $300 lifter into a $3,000 camshaft and lifter replacement. The issue affects 2007+ Suburbans and is one of the most complained-about GM V8 problems. GM switched from 4-cylinder AFM to 17-pattern DFM in 2019, but lifter failures continue.

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 1996-1999 Vortec's distributor sits nearly vertical, and its ventilation design allows moisture and condensation to accumulate inside the cap. This causes corrosion, carbon tracking, and cracking of the cap and rotor, producing intermittent misfires and stalling, especially in damp conditions. It is common enough that owners report replacing the cap and rotor roughly annually, and aftermarket ignition parts tend to fail faster than AC Delco/GM originals.

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).

L87 6.2L V8s built March 1, 2021 through May 31, 2024 can suffer sudden rod-bearing failure and engine seizure with loss of propulsion. GM attributes it to supplier manufacturing/quality issues — sediment/debris left on connecting rods and in crankshaft oil galleries plus out-of-spec dimensions — that starve and pound the rod bearings. NHTSA safety recall 25V-274 (April 2025) covers 44,802 Tahoes among ~600k GM full-size trucks/SUVs; GM logged over 14,000 field complaints and a dozen alleged crashes/injuries. NHTSA has since opened follow-up query RQ26001 into failures on engines outside the recall and on some units that failed after the dealer remedy.

Timing chain tensioner fails allowing chain to slap and jump timing. 2.5L V6 particularly susceptible. Can cause valve damage if chain jumps more than one tooth.

The 2.5L Suzuki V6 engine has a hydraulic timing chain tensioner that leaks down overnight, causing a loud rattling noise on cold startup. If the tensioner fails completely, the timing chain can jump and cause valve-to-piston contact, bending valves and potentially destroying the engine.

Second-generation Traverse owners report the 3.6L LFY V6 consuming oil at roughly 1 quart every 1,000-2,000 miles, with some AWD examples burning a half-quart per 1,000 miles starting around 55k miles. Root causes are worn/coked piston rings and a PCV system that pulls oil vapor into the intake. Because there is often no visible leak, owners discover it only when the low-oil light comes in or the engine runs low between changes, risking accelerated wear if not topped up.