P0300 on a 2019 Toyota Rav4
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 Rav4
Ranked from 869 NHTSA owner complaints filed for this vehicle.
- 1
Coolant Intrusion into Cylinder (Head Gasket/Engine Block Failure)
High severityCoolant leaking into the cylinders (especially cylinder #2) causes misfires and rough running, often accompanied by white smoke and overheating.
Reported in 3 NHTSA complaints - 2
Faulty Spark Plugs
Low severityWorn or fouled spark plugs fail to ignite the air/fuel mixture properly, leading to random or multiple cylinder misfires.
Common cause - 3
Defective Ignition Coils
Medium severityA failing ignition coil will not provide sufficient voltage to the spark plug, causing the cylinder to misfire under load.
Common cause - 4
Fuel Delivery Issues (Clogged Injectors or Low Fuel Pressure)
Medium severityRestricted fuel injectors or a failing fuel pump can cause a lean condition, resulting in random misfires across multiple cylinders.
Common cause - 5
Vacuum Leaks / Intake Manifold Leaks
Medium severityUnmetered air entering the intake manifold disrupts the air/fuel ratio, causing lean misfires that trigger a P0300 code.
Common cause - 6
Mass Air Flow (MAF) Sensor Failure
Low severityA dirty or faulty MAF sensor provides incorrect airflow data to the ECM, leading to improper fueling and random misfires.
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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