P0300 on a 2019 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 2019 Toyota Camry
Ranked from 385 NHTSA owner complaints filed for this vehicle.
- 1
Engine Coolant Bypass Valve failure
High severityWhile typically setting its own code (P26CB/P26AE), severe coolant system issues can lead to overheating and subsequent engine running issues or misfires. Confirmed by checking for bypass valve codes and overheating.
Reported in 5 NHTSA complaints - 2
Blown head gasket
High severityCoolant leaking into the cylinders can cause severe misfires and engine damage. Confirmed by coolant loss, overheating, and combustion gases in the cooling system.
Reported in 2 NHTSA complaints - 3
Faulty Engine Control Module (ECM)
High severityA failing ECM can send incorrect signals to the ignition or fuel systems, causing misfires. Confirmed by ECM diagnostics or internal faults.
Reported in 2 NHTSA complaints - 4
Fuel injector failure or clogging
Medium severityA clogged or failing fuel injector can cause a lean misfire. Confirmed by injector flow testing or checking for injector codes.
Reported in 1 NHTSA complaint - 5
Faulty spark plugs
Low severityWorn or fouled spark plugs are a primary cause of misfires. Look for worn electrodes or carbon buildup.
Common cause - 6
Faulty ignition coils
Medium severityA failing ignition coil will not provide enough voltage to spark the plug, causing a misfire. Confirmed by testing coil resistance or swapping coils to see if the misfire moves.
Common cause - 7
Vacuum leak
Medium severityUnmetered air entering the intake manifold can cause a lean condition and random misfires. Look for cracked hoses or intake manifold gasket leaks.
Common cause - 8
Low fuel pressure
Medium severityA failing fuel pump or clogged fuel filter can starve the engine of fuel, leading to random misfires. Confirmed by testing fuel pressure at the rail.
Common cause
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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