P0300 on a 2019 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 2019 GMC Sierra 1500
Ranked from 608 NHTSA owner complaints filed for this vehicle.
- 1
Lifter failure / collapse
High severityThe hydraulic valve lifters fail or collapse, often causing a loud ticking or knocking noise, rough idle, and misfires. This can lead to camshaft damage and severe engine failure.
Reported in 8 NHTSA complaints - 2
Camshaft damage / failure
High severityFailed lifters can cause abnormal contact with the camshaft lobe, resulting in significant scoring, wear, or failure of the camshaft, leading to misfires and engine damage.
Reported in 4 NHTSA complaints - 3
Connecting rod bearing failure
High severityDefective connecting rod bearings can fail, causing lower-end engine knocking, loss of compression, and catastrophic engine seizure.
Reported in 3 NHTSA complaints - 4
Bent pushrod
High severityA collapsed or failed lifter can cause the pushrod to bend, leading to a loss of proper valve operation and resulting in a cylinder misfire.
Reported in 1 NHTSA complaint - 5
Cracked cylinder head / Coolant intrusion
High severityA cracked cylinder head can allow coolant to mix with oil, causing contamination, internal engine damage, and persistent misfires.
Reported in 1 NHTSA complaint - 6
Failed piston ring / Scored engine block
High severityA failed piston ring can score the engine block, leading to a loss of compression, misfires, and the need for a complete engine replacement.
Reported in 1 NHTSA complaint - 7
Faulty spark plugs
Low severityWorn or fouled spark plugs fail to ignite the air/fuel mixture properly, causing a misfire. This is a standard check for P0300.
Common cause - 8
Faulty ignition coils
Low severityA failing ignition coil will not provide sufficient voltage to the spark plug, resulting in a weak or absent spark and causing a misfire.
Common cause - 9
Clogged or faulty fuel injectors
Medium severityIf a fuel injector is clogged or failing, it will not deliver the correct amount of fuel to the cylinder, leading to a lean misfire.
Common cause - 10
Vacuum leaks
Medium severityUnmetered air entering the intake manifold can cause a lean condition, leading to random or multiple cylinder misfires.
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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