P0300 on a 2020 Jeep Gladiator
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 2020 Jeep Gladiator
Ranked from 478 NHTSA owner complaints filed for this vehicle.
- 1
Camshaft lobe wear / rocker arm-lifter failure (3.6L Pentastar defect)
High severityAn unusually large cluster of owners report worn or scored intake camshaft lobes and failing rocker arms/lifters causing multiple cylinder misfires, engine ticking, and eventual engine failure; multiple complaints cite the FCA/Stellantis TSBs (09-011-25, 18-024-21) covering this exact defect.
Reported in 11 NHTSA complaints - 2
Coolant intrusion into cylinders from head gasket/cylinder head failure
High severityReported head gasket failure and a cracked cylinder head let coolant leak into the combustion chambers, fouling cylinders and producing rough-running/misfire symptoms alongside overheating.
Reported in 2 NHTSA complaints - 3
Failed ignition coil pack and spark plugs
Medium severityOne owner pulled codes P0300/P0301/P0305/P0420, replaced coil packs and plugs, and the misfire code returned; coil/plug failure is a directly documented trigger on this vehicle even though the dealer later blamed aftermarket parts.
Reported in 1 NHTSA complaint - 4
Worn spark plugs
Low severityWorn or fouled plugs produce a weak spark that can't reliably ignite the mixture, especially under load.
Common causeParts:spark plugs - 5
Vacuum or intake leaks
Medium severityUnmetered air entering past a cracked hose or gasket leans out one or more cylinders enough to cause a misfire.
Common cause - 6
Carbon-fouled intake valves
Low severityDirect-injection engines like the Pentastar are prone to carbon buildup on the intake valves, disrupting airflow and atomization at a given cylinder.
Common cause - 7
Low cylinder compression from worn rings or valves
High severityReduced compression on a cylinder prevents proper combustion and registers as a misfire on that cylinder.
Common cause - 8
EGR valve fault
Medium severityA stuck-open EGR valve over-dilutes the intake charge, which can cause a rough idle and misfire counts.
Common causeParts: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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