P0300 on a 2018 Kia Soul

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 Kia Soul

Ranked from 211 NHTSA owner complaints filed for this vehicle.

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1
Worn piston rings / low cylinder compression (known Kia GDI engine defect)
High severity
Multiple owners had shop-confirmed low or zero compression on specific cylinders traced to worn piston rings, a documented failure mode on these 1.6L/2.0L GDI engines that directly produces a random/multi-cylinder misfire.
Reported in 6 NHTSA complaints
2
Spark plug fouling from chronic oil consumption
Medium severity
Owners report the engine burning a quart of oil every few hundred miles; oil pulled past worn rings/valve seals fouls the plugs and produces a rough-running, misfiring engine.
Reported in 5 NHTSA complaints
3
Rod bearing failure / engine knock
High severity
Several complaints describe a developing rod knock or a crankshaft-related code shortly before misfire and engine failure, consistent with the rod-bearing wear defect covered by Kia's engine class-action settlement.
Reported in 3 NHTSA complaints
4
Clogged or leaking fuel injector
Medium severity
One owner had all four injectors replaced for a related failure; a dirty or leaking injector starves or floods a cylinder and causes a misfire.
Reported in 1 NHTSA complaint
Parts:fuel injector
5
Worn or fouled spark plugs
Low severity
Aged, gapped-out, or oil-fouled plugs are the most common general cause of a random misfire; pull and inspect plugs first.
Common cause
Parts:spark plug
6
Failing ignition coil(s)
Medium severity
A cracked or weak coil produces an intermittent spark, usually isolating to one cylinder but sometimes reading as random misfire; swap coils cylinder-to-cylinder to confirm.
Common cause
Parts:ignition coil
7
Vacuum or intake leak
Low severity
Unmetered air entering after the MAF sensor leans out one or more cylinders enough to misfire, especially at idle.
Common cause
8
EGR valve fault
Low severity
A stuck-open EGR valve dilutes the intake charge with excess exhaust gas at idle, which can cause rough running and a misfire code.
Common cause
Parts: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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Matching symptoms

Car Runs Rough Flashing Check Engine Light