P0300 on a 2018 Toyota Camry

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 Toyota Camry

Ranked from 727 NHTSA owner complaints filed for this vehicle.

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1
Coolant intrusion into cylinders from electric water pump failure
High severity
Multiple owners report the electric water pump failing outright (including a stored actuator-stuck code), and in one case coolant reaching the engine and clogging a fuel injector — both cause rough-running/misfire and stalling.
Reported in 5 NHTSA complaints
Parts:water pump
2
Individual cylinder misfire from a fouled/failing ignition component
Medium severity
One owner's scan confirmed a cylinder-4 misfire (P0304) with shaking and multiple warning lights — a textbook single-cylinder ignition/injector fault feeding the broader random-misfire code.
Reported in 1 NHTSA complaint
Parts:ignition coil spark plugs
3
Worn spark plugs
Low severity
Standard wear item; a widened gap misfires under load, especially on a direct-injection engine with higher cylinder pressures.
Common cause
Parts:spark plugs
4
Clogged or failing fuel injector
Medium severity
A partially clogged or dribbling injector leans out or floods an individual cylinder.
Common cause
Parts:fuel injector
5
Vacuum or intake leak
Low severity
Unmetered air after the MAF leans a cylinder enough to misfire, most noticeable at idle.
Common cause
6
Carbon-fouled intake valves (direct-injection buildup)
Low severity
Direct-injection engines don't wash the back of the intake valves with fuel, allowing carbon buildup that disrupts airflow and can cause intermittent misfire.
Common cause
7
Low cylinder compression (worn rings or valves)
High severity
Mechanical wear reduces cylinder sealing enough that combustion is incomplete.
Common cause
8
EGR valve stuck open or faulty
Low severity
Excess recirculated exhaust gas dilutes the intake charge and can trigger a misfire at idle/light load.
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