P0300 on a 2015 GMC Yukon
P0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.
Not your vehicle? See general P0300 info.
Most common causes on the 2015 GMC Yukon
Ranked from 546 NHTSA owner complaints filed for this vehicle.
- 1
Collapsed AFM (Active Fuel Management) lifter / camshaft lobe wear
High severityThis is the dominant, extensively documented failure mode in this batch: collapsed hydraulic lifters and worn camshaft lobes on the AFM-equipped 5.3L/6.2L V8 cause a tick/knock, shake, and misfire; one complaint's shop diagnosis was literally a P0300 random misfire tied to a rod-knock/compression failure from this same root cause.
Reported in 12 NHTSA complaints - 2
Clogged or failing fuel injector(s)
Medium severityOne owner had all 8 injectors replaced for rough idling; a dirty or leaking injector unbalances an individual cylinder's fuel delivery enough to misfire.
Reported in 1 NHTSA complaintParts:fuel injector - 3
Low cylinder compression from valvetrain damage
High severityA mechanic diagnosed a compression failure in one cylinder tied to engine damage requiring replacement, consistent with lifter/cam wear progressing to valve or piston damage.
Reported in 1 NHTSA complaint - 4
Worn spark plugs
Low severityFouled or worn plugs are a standard misfire cause; note one owner replaced plugs, wires, and the coil for a confirmed P0303 without resolving the shake, suggesting a deeper mechanical cause on that truck.
Common causeParts:spark plug - 5
Failing ignition coil(s)
Low severityA weak or intermittently failing coil drops spark energy to one cylinder, producing a repeatable single-cylinder misfire.
Common causeParts:ignition coil - 6
Vacuum leak (intake manifold gasket or PCV hose)
Medium severityUnmetered air entering through a cracked hose or manifold gasket leans out a cylinder enough to misfire, especially at idle.
Common causeParts:intake manifold gasket - 7
EGR valve fault
Low severityA stuck-open EGR valve introduces excess inert exhaust gas into a cylinder, disrupting combustion enough to misfire, especially at idle.
Common causeParts:EGR valve
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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0300 on your car still needs shop confirmation before any repair.
Common symptoms
- Flashing or steady check engine light
- Rough idle
- Shaking under acceleration
- Loss of power
- Fuel smell from exhaust
What to check before replacing parts
Scan for cylinder-specific misfire codes
Look for: A companion P0301–P0308 pins the misfire to one cylinder — start there. P0300 with no cylinder code points at something hitting several at once: fuel pressure, a large vacuum leak, or timing.
Inspect the spark plugs and coils
Look for: Pull the plugs: black/sooty = rich, oily = oil intrusion, white/blistered = lean or overheating, cracked porcelain or an out-of-spec gap = replace. Then swap a coil to another cylinder — if a cylinder-specific code follows the coil, the coil is bad.
Check fuel trims for a vacuum leak
Look for: High positive short- and long-term trims (worst at idle, improving as RPM rises) mean unmetered air is getting in. Smoke-test the intake and listen for hissing.
Verify fuel pressure
Look for: Compare running/cranking pressure to the vehicle spec. Low or dropping pressure starves multiple cylinders and reads as a random misfire — suspect the pump, filter, or regulator.
Compression / leak-down test if ignition and fuel check out
Look for: A cylinder 15%+ below the others, or leak-down hissing from the intake (intake valve), exhaust (exhaust valve), or oil filler (rings), means the misfire is mechanical — not a swap-in part.
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