P0300 on a 2019 Jeep Grand Cherokee
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 Jeep Grand Cherokee
Ranked from 356 NHTSA owner complaints filed for this vehicle.
- 1
Failed Head Gasket / Coolant Intrusion
High severityCoolant leaks into the combustion chamber, causing misfires, rough idle, overheating, and white smoke from the exhaust.
Reported in 5 NHTSA complaints - 2
Worn Camshaft / Lifters / Rocker Arms (Pentastar Tick)
High severityPremature wear on the camshaft lobes, lifters, or rocker arms causes improper valve operation, leading to severe misfires and a ticking noise from the engine.
Reported in 4 NHTSA complaints - 3
Cracked Plastic Oil Cooler Assembly
High severityThe plastic oil cooler cracks, causing massive oil or coolant leaks, which can lead to engine overheating, misfires, or catastrophic engine failure.
Reported in 2 NHTSA complaints - 4
Faulty Spark Plugs
Low severityWorn or fouled spark plugs fail to ignite the air-fuel mixture properly, resulting in random or multiple cylinder misfires.
Common cause - 5
Faulty Ignition Coils
Medium severityA failing ignition coil cannot provide sufficient voltage to the spark plug, causing the cylinder to misfire.
Common cause - 6
Vacuum Leak
Medium severityUnmetered air enters the intake manifold, causing a lean air-fuel mixture that leads to random misfires across multiple cylinders.
Common cause - 7
Clogged or Failing Fuel Injectors
Medium severityRestricted fuel flow prevents the proper air-fuel mixture from reaching the cylinders, causing misfires.
Common cause - 8
Low Fuel Pressure
Medium severityA failing fuel pump or clogged fuel filter starves the engine of fuel, causing a lean condition 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.
Rather have a pro handle it? Find a vetted local mechanic.