P0300 on a 2017 Hyundai Santa Fe
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 Hyundai Santa Fe
Ranked from 943 NHTSA owner complaints filed for this vehicle.
- 1
Theta II connecting-rod bearing wear causing low compression/knock misfire
High severityA very large share of complaints in this batch describe chronic excessive oil consumption, engine knocking, and eventual seizure/failure — the well-documented Theta II bearing-wear defect that causes low compression and misfire before catastrophic failure.
Reported in 10 NHTSA complaints - 2
Rough-running/misfire-like symptoms after Hyundai Campaign 9C2 ECU recalibration
Medium severitySeveral owners report new hesitation, surging, or high cold-start RPM immediately after the 9C2 'Theta II emissions' software update, suggesting the revised fueling/timing maps are provoking misfire-like drivability symptoms.
Reported in 6 NHTSA complaints - 3
Worn spark plugs
Low severityEroded or fouled plugs increase the voltage needed to fire the mixture and are a leading cause of random misfire; inspect gap and condition.
Common causeParts:spark plug - 4
Failing ignition coil(s)
Medium severityA weak or intermittently failing coil-on-plug drops spark energy to one cylinder; swapping coils between cylinders and watching the misfire follow confirms it.
Common causeParts:ignition coil - 5
Clogged or leaking fuel injector
Medium severityAn injector delivering too little or too much fuel to a cylinder produces a repeatable, cylinder-specific misfire.
Common causeParts:fuel injector - 6
Vacuum/intake leak
Medium severityUnmetered air entering the intake leans one or more cylinders enough to misfire, especially at idle.
Common causeParts:intake gasket - 7
Carbon-fouled intake valves (direct-injection buildup)
Low severityGDI engines like the Theta II accumulate carbon on the backs of the intake valves over time, disrupting airflow/atomization enough to cause a rough idle or misfire.
Common cause
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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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