P0300 on a 2018 Hyundai Santa Fe Sport
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 2018 Hyundai Santa Fe Sport
Ranked from 414 NHTSA owner complaints filed for this vehicle.
- 1
Worn connecting rod bearings / low compression from Theta II oil-starvation defect
High severityMultiple owners report engine banging/seizing-like knock diagnosed as connecting-rod bearing failure tied to the well-documented Theta II oil-consumption defect; worn rod bearings and rings drop compression enough to cause a random misfire.
Reported in 3 NHTSA complaints - 2
Burned or worn exhaust/intake valves
High severityOwners report recurring valve and cylinder failures ("engine valves and cylinders keep failing") and a burned valve found on teardown, both of which drop cylinder compression and cause misfire.
Reported in 3 NHTSA complaints - 3
Oil-fouled spark plugs from excessive oil consumption
Medium severityOne owner's complaint explicitly cites the engine design causing "ruined spark plugs" from the chronic oil-burning defect; fouled plugs misfire under load.
Reported in 1 NHTSA complaintParts:spark plugs - 4
Electrical/wiring fault in the ignition circuit
Medium severityAn independent mechanic told one owner an electrical fault (separate from prior repairs) was directly causing the engine to misfire.
Reported in 1 NHTSA complaint - 5
Worn spark plugs (normal wear)
Low severityStandard high-mileage wear item; a worn or improperly gapped plug will not fire consistently under load.
Common causeParts:spark plugs - 6
Failing ignition coil(s)
Medium severityA cracked or weak coil drops spark energy to one cylinder, producing a repeatable single- or multi-cylinder misfire.
Common causeParts:ignition coil - 7
Vacuum or intake leak
Medium severityUnmetered air leaning out one or more cylinders causes an intermittent misfire, often worse at idle.
Common cause - 8
Clogged or leaking fuel injector
Medium severityA restricted or dribbling injector starves or floods a cylinder, producing a repeatable misfire on that cylinder.
Common causeParts:fuel injector - 9
EGR valve stuck open
Low severityExcess exhaust gas recirculated at idle/light load dilutes the intake charge enough to cause a rough-running misfire.
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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