P0300 on GMC: How to Diagnose & Fix

The GMC Yukon 5.3L (L83, LC9, LMG) and 6.2L (L94, L86) V8 engines use Active Fuel Management (AFM) cylinder deactivation. The special collapsible AFM lifters on cylinders 1, 4, 6, and 7 fail prematurely, causing misfires, engine ticking, rough idle, and potential catastrophic damage. This is the single most reported mechanical failure on GMT900 (2007-2014) and K2XX (2015-2020) Yukon models. GM issued diagnostic bulletins PIP4568 (2007-2014 AFM V8s) and PIP5259 (2014-2015 Yukon) covering collapsed or stuck AFM lifters. Yukon models used as daily drivers with lots of highway cruising (where AFM activates most) are most susceptible. On 2007-2014 engines the VLOM (Valve Lifter Oil Manifold), which controls oil flow to the AFM lifters, is replaced along with the lifters per PIP4568.

GM bulletin 10-06-01-008M covers 2007–2014 GMC Yukon models with listed Active Fuel Management engines, including the 5.3L LC9. GM attributes the excessive oil consumption, typically noticed at higher mileage (about 30,000–40,000 miles), to oil pulled through the PCV system or oil spray discharged from the AFM pressure-relief valve in the crankcase, which can build deposits in the piston-ring grooves and foul spark plugs. GM treats more than 1 quart per 2,000–3,000 miles as excessive. External leaks and other causes still need to be ruled out.

The LML Duramax EGR (exhaust gas recirculation) cooler is prone to coolant leaks internally, allowing coolant to enter the intake manifold and combustion chambers. Coolant in the intake causes white smoke, rough running, and potential hydrolocking of cylinders. The EGR valve also sticks open or closed from carbon buildup, causing rough idle, black smoke, and check engine lights. The EGR cooler failure can occur as early as 60,000 miles on trucks used in stop-and-go driving. GM bulletin 08-06-04-003D provides the EN-48974 adapter set for pressure-testing the EGR cooler for coolant leaks into the combustion chambers.

The 4.3L Vortec in the Safari uses a central port injection system ('spider injector') that develops poppet valve sticking and fuel line cracks. This causes hard starting, rough idle, and a strong fuel smell from leaking fuel inside the intake manifold.

On the Yukon XL with the 5.3L or 6.2L V8 and Active Fuel Management (AFM, also called Displacement on Demand or DOD), the AFM valve lifters can fail. These lifters collapse on purpose so the engine can shut off cylinders to save fuel. When one sticks collapsed, or its internal locking pin is damaged, the valve above it stops moving. The result is a ticking noise, a misfire, and a check engine light, and the camshaft lobe under the lifter can be damaged. GM service bulletin 15-06-01-002E (October 2016) covers 2015-2017 Yukon and Yukon XL with the 5.3L (L83) or 6.2L (L86). It lists three causes: an AFM lifter that is mechanically collapsed or stuck all the time, damage to the lifter's internal locking pin from oil aeration, and a lifter that has collapsed and is stuck in its bore. Owners of earlier trucks report the same kind of lifter tick. One 2007 Yukon 5.3L owner reports a tick that gets louder when the engine is warm, and in the same thread another owner says the tick came back years after a dealer replaced the lifters.

The GM Ecotec 2.4L in the 2010-2014 Terrain has the same timing chain stretch and tensioner failure as the Equinox and Malibu. GM Special Coverage 12313 covers balance-chain stretch (worn chrome on the balance chain pins) on 2010-2011 models for 10 years/120,000 miles. The 2010-2011 models are worst affected. Piston ring wear on 2010-2013 models causes excessive oil burning (GM bulletin 13-06-01-003), which leads to low oil and accelerated timing chain wear. 2015+ models received revised internal components.

On the second-generation Terrain (2018+) with the turbocharged 1.5L LYX/LSD or 2.0L LTG engine, the air-to-air charge air cooler (intercooler) accumulates condensate from humid or rainy driving plus PCV-borne moisture. In cold ambient temperatures that water freezes inside the CAC core, restricting charge airflow. GM documents this in service bulletin 18-NA-020, first released in January 2018 and later expanded through the 2024 model year. Owners on the Terrain/Equinox forum describe ice and standing water inside the charge tube. Here the cooler itself is blocked by ice or contamination; the duct has not come off the throttle body.

On the 5.7L Vortec V8, the central sequential fuel injection (CSFI) "spider" assembly's poppet nozzles clog and its fuel lines crack.

GM says a misfire, tick noise and check-engine light with P0300 may be caused by an Active Fuel Management lifter that is mechanically collapsed or stuck, internal locking-pin damage from oil aeration, a lifter collapsed and stuck in its bore, or a bent pushrod. 2014 GMC Sierra 1500, 2015-2018 GMC Sierra and 2019 GMC Sierra Limited with the 5.3L V8 (L83) or 6.2L V8 (L86), per GM bulletin 15-06-01-002O (March 2023). The 4.3L V6 is not listed.

GM says major carbon build-up on the intake and/or exhaust valves, from fuel contamination or incomplete burning of the fuel, can cause rough idle, extended crank, crank-no-start or misfire with codes P0300-P0308, and that valves may stick. 2014-2018 GMC Sierra 1500 gasoline engines (4.3L V6, 5.3L V8, 6.2L V8); GM bulletin 16-NA-383 (June 2024) covers all 2000-2025 GM gasoline passenger cars and light/medium-duty trucks.

The 3.6L V6 with Active Fuel Management experiences failure of the switching roller finger followers (SRFF) on the deactivating cylinders 2 and 5, where a locking pin sticks or binds or the pin shelf breaks or wears, setting the check-engine light with codes P219A/P219B and, in some cases, causing a ticking noise. A damaged follower or lash adjuster can become dislodged if not addressed.