P0300 on a 2011 Toyota Corolla

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 2011 Toyota Corolla

Ranked from 590 NHTSA owner complaints filed for this vehicle.

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1
Low cylinder compression from oil consumption / worn piston rings
High severity
Three owners reported high oil consumption alongside a misfire code and check-engine light, with dealers recommending cylinder/ring work; worn rings or valve seals reduce compression enough to misfire.
Reported in 3 NHTSA complaints
Parts:piston rings
2
Fouled or fuel-wetted spark plugs from engine flooding
Medium severity
Two owners had a misfire (one an explicit P0303 code) traced to spark plugs soaked/fouled by excess fuel, requiring the dealer to clean plugs and cylinders.
Reported in 2 NHTSA complaints
Parts:spark plugs
3
Failing ignition coil
Medium severity
A weak coil drops spark energy on one cylinder, causing an intermittent misfire that a scan tool will identify by cylinder.
Common cause
Parts:ignition coil
4
Clogged or leaking fuel injector
Medium severity
A restricted injector starves a cylinder while a leaking one floods it; either produces a repeatable misfire on that cylinder.
Common cause
Parts:fuel injector
5
Vacuum or intake leak
Medium severity
Unmetered air leaning out one or more cylinders is a common and inexpensive-to-rule-out misfire cause.
Common cause
6
Carbon-fouled intake valves
Low severity
Carbon deposits disrupt airflow and fuel atomization at the valve, contributing to a rough-running/misfiring cylinder as mileage accumulates.
Common cause
7
EGR system fault
Low severity
Excess or erratic exhaust gas recirculation dilutes the intake charge enough to cause a misfire, particularly at idle or light load.
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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Matching symptoms

Car Runs Rough Flashing Check Engine Light