P0300 on a 2017 GMC Sierra 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 2017 GMC Sierra 1500

Ranked from 425 NHTSA owner complaints filed for this vehicle.

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1
Active Fuel Management (AFM) Lifter Failure
High severity
Look for a ticking/tapping noise from the top of the engine, misfires, and bent pushrods. Confirmed by inspecting the lifters and camshaft for damage or collapse, particularly on AFM cylinders.
Reported in 13 NHTSA complaints
2
Fuel Injector Failure
Medium severity
Look for rough running, shuddering, and check engine light illumination. Confirmed by fuel trim codes (like 219a) or misfire codes, and testing injector flow/resistance.
Reported in 3 NHTSA complaints
3
Worn Crankshaft Bearings / Connecting Rod Failure
High severity
Look for engine knocking, loss of oil pressure, or complete engine failure. Confirmed by inspecting the bottom end for metal shavings and measuring bearing clearances.
Reported in 2 NHTSA complaints
4
Faulty Ignition Coil
Low severity
Look for engine misfires, rough idle, and flashing check engine light. Confirmed by swapping the coil to another cylinder and seeing if the misfire follows.
Reported in 1 NHTSA complaint
5
Worn Spark Plugs
Low severity
Look for general misfires, poor fuel economy, and rough idle. Confirmed by visual inspection of the spark plug electrodes for excessive wear or fouling.
Common cause
6
Vacuum Leak
Medium severity
Look for a high or fluctuating idle and lean codes accompanying the misfire. Confirmed by performing a smoke test on the intake manifold and vacuum lines.
Common cause

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