P0300 on a 2017 Hyundai Elantra Gt

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 Elantra Gt

Ranked from 732 NHTSA owner complaints filed for this vehicle.

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1
Engine bearing wear / rod knock from Theta II manufacturing debris (KSDS recall / Recall 203)
High severity
Many owners describe catastrophic engine failure with rod knock, engine seizure, or being placed in KSDS-related limp mode after the recall ECU flash — a well-documented Theta II bearing-wear defect that produces rough running and misfire-pattern symptoms before full failure.
Reported in 10 NHTSA complaints
2
Excessive oil consumption / engine sludge leading to low compression
High severity
Several owners report chronic oil-burning and dealer-confirmed sludge/metal-shaving buildup, consistent with the low-compression/worn-ring misfire pattern on this engine family.
Reported in 5 NHTSA complaints
3
Ignition coil failure (repeated coil-pack failures)
High severity
Owners report ignition coils failing outright — one confirming a cylinder-2 misfire via OBD reader that recurred after swapping coils, another reporting all four coils blown before 60,000 miles and repeated coil replacements after recurring check-engine lights.
Reported in 3 NHTSA complaints
Parts:ignition coil spark plug
4
Timing chain or camshaft (VVT) phaser wear
Medium severity
Multiple mechanics diagnosed timing chain looseness or camshaft/phaser wear on shuddering, stalling vehicles in this batch, consistent with a valve-timing-related misfire.
Reported in 3 NHTSA complaints
Parts:timing chain camshaft phaser
5
Failing crankshaft position sensor
Medium severity
One owner's shop replaced the crankshaft sensor while chasing a stalling complaint — a faulty crank sensor produces erratic timing signals that manifest as misfire.
Reported in 1 NHTSA complaint
Parts:crankshaft position sensor
6
Worn or fouled spark plugs
Low severity
Standard wear item; worn plugs produce weak spark and intermittent misfire, especially under load or acceleration.
Common cause
Parts:spark plug
7
Vacuum or intake leak
Medium severity
Unmetered air leaning out one or more cylinders can produce a random/multiple misfire pattern.
Common cause
Parts:intake gasket vacuum hose
8
Clogged or leaking fuel injector
Medium severity
A partially clogged or leaking injector disrupts the air/fuel ratio in that cylinder enough to cause a repeatable misfire.
Common cause
Parts:fuel injector

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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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Matching symptoms

Car Runs Rough Flashing Check Engine Light