P0300 on a 2019 GMC Sierra Limited 1500

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 2019 GMC Sierra Limited 1500

Ranked from 405 NHTSA owner complaints filed for this vehicle.

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1
Collapsed valve lifter or worn camshaft lobe (5.3L/6.2L Gen V small-block)
High severity
This vehicle's complaints show a strong, repeated pattern of lifter and camshaft failure — collapsed/frozen lifters and cracked or worn camshaft lobes causing loud knocking, violent shaking, and multi-cylinder misfire, a widely-documented AFM/DFM lifter issue on this engine family.
Reported in 8 NHTSA complaints
Parts:valve lifter camshaft
2
Fouled or worn spark plugs / ignition components
Medium severity
One owner documented a cylinder-8 misfire (P0308) with backfiring and ticking that was addressed by replacing spark plugs and ignition components; another replaced spark plugs and injectors while chasing a misfire/rough-run complaint.
Reported in 2 NHTSA complaints
Parts:spark plugs ignition coil
3
Clogged or failing fuel injector(s)
Medium severity
Two owners had all fuel injectors replaced while troubleshooting misfiring and rough-running symptoms on this truck.
Reported in 2 NHTSA complaints
Parts:fuel injector
4
Vacuum leak from a failed intake manifold gasket
Medium severity
One owner replaced the intake manifold gasket as part of resolving a misfiring, rough-running, backfiring complaint, indicating an unmetered-air path contributing to the misfire.
Reported in 1 NHTSA complaint
Parts:intake manifold gasket
5
Failing ignition coil
Medium severity
A weak or failing coil produces a cylinder-specific misfire that can look like a random misfire as it rotates between cylinders; swap coils to confirm.
Common cause
Parts:ignition coil
6
Vacuum or intake air leak (unrelated to gasket)
Medium severity
Cracked intake boots or PCV hoses let in unmetered air, leaning the mixture and causing rough idle/misfire; smoke-test the intake tract.
Common cause
7
EGR valve fault
Low severity
A stuck or leaking EGR valve dilutes the intake charge and can cause rough idle and misfire at light load; test valve movement and passages.
Common cause
Parts: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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Matching symptoms

Car Runs Rough Flashing Check Engine Light