P0300 on a 2018 Jeep Grand Cherokee Trackhawk
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 Jeep Grand Cherokee Trackhawk
Ranked from 685 NHTSA owner complaints filed for this vehicle.
- 1
Blown or failing head gasket letting coolant into a cylinder
High severityThis is the dominant complaint pattern for this 3.6L: owners report coolant burning in a specific cylinder, head gaskets "blowing" around 80-100k miles, and liquid draining into the cylinders — coolant intrusion fouls plugs and kills compression in that cylinder.
Reported in 6 NHTSA complaintsParts:head gasket - 2
Worn spark plugs or failing ignition coils
High severityMultiple owners had plugs and coils replaced while chasing a rough-running misfire, and one had a spark plug directly diagnosed as misfiring by an independent shop.
Reported in 3 NHTSA complaints - 3
EGR valve or EGR cooler failure (carbon-clogged or cracked)
Medium severityOwners report a cracked EGR cooler (recurrence of a prior recall repair) and an EGR valve/intake failure with heavy carbon deposits, both of which disrupt combustion and can trigger a misfire.
Reported in 3 NHTSA complaints - 4
Coolant loss from a failing water pump fouling a cylinder
Medium severityOwners report a water-pump design flaw causing persistent coolant leaks and repeated low-coolant episodes that preceded a misfire code.
Reported in 2 NHTSA complaintsParts:water pump - 5
Worn camshaft lobes / rocker arms
Medium severityAn owner reports worn rockers and camshaft causing a ticking noise at only 86k miles, a wear pattern that can reduce valve lift on affected cylinders and produce a misfire.
Reported in 1 NHTSA complaint - 6
Vacuum or intake leak
Medium severityUnmetered air causes a lean, rough-running misfire, typically worse at idle.
Common cause - 7
Clogged or leaking fuel injector
Medium severityA restricted or dribbling injector starves or floods a cylinder and produces a repeatable misfire on that cylinder.
Common causeParts:fuel injector - 8
Carbon-fouled intake valves
Low severityDirect-injection engines accumulate intake-valve carbon that disrupts airflow/atomization and can trigger a rough-running misfire.
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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