P0300 on a 2017 Hyundai Tucson Fuel Cell
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 Tucson Fuel Cell
Ranked from 983 NHTSA owner complaints filed for this vehicle.
- 1
Worn piston rings/cylinder bores causing low compression and oil consumption (known 1.6L GDI engine defect)
High severityThis engine family is subject to multiple NHTSA oil-consumption/engine-failure recalls; this batch is dominated by reports of knocking, shaking, rough running, and confirmed misfires tied to heavy oil consumption and, in one case, a compression test showing two cylinders with no compression.
Reported in 9 NHTSA complaints - 2
Connecting rod/rod bearing failure
High severityCatastrophic internal failure reported in this batch (a connecting rod broke and punched through the oil pan at only 54k miles), which manifests as sudden severe misfire/knock before total engine failure.
Reported in 1 NHTSA complaint - 3
Broken spark plug ceramic insulator from pre-ignition/detonation
High severityA complaint in this batch describes misfiring traced to two spark plugs with cracked ceramic insulators pushed into the cylinder, consistent with detonation events.
Reported in 1 NHTSA complaintParts:spark plugs - 4
Turbocharger wastegate actuator failure
Medium severityA reported wastegate actuator stuck fully open causes erratic boost control that can produce rough running/power loss under load.
Reported in 1 NHTSA complaint - 5
Failing ignition coil(s)
Medium severityStandard random-misfire cause; a weak coil produces an intermittent spark that swaps cylinders.
Common causeParts:ignition coil - 6
Vacuum or intake leak
Medium severityUnmetered air leans out individual cylinders and destabilizes idle combustion.
Common cause - 7
Clogged or leaking fuel injector
Medium severityA restricted or dripping direct injector starves or floods a cylinder, producing a repeatable misfire on that cylinder.
Common causeParts:fuel injector - 8
Carbon-fouled intake valves
Medium severityCommon on direct-injection engines; buildup on valve backs disrupts airflow and atomization, causing intermittent 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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