P0300 on a 2014 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 2014 Jeep Grand Cherokee
Ranked from 2,369 NHTSA owner complaints filed for this vehicle.
- 1
Failed Rocker Arms / Lifters / Camshaft (Pentastar 3.6L)
High severityThe 3.6L Pentastar engine is known for rocker arm needle bearing failures, which cause camshaft scoring, a loud ticking noise, and misfires (P0300/P0302). Look for a prominent engine tick and inspect the valvetrain for worn rocker arms and scored cam lobes.
Reported in 4 NHTSA complaints - 2
Cylinder Head Failure
High severityThe 3.6L engine has a known history of left cylinder head valve seat issues causing misfires. A leak down test or compression test confirming loss of compression on specific cylinders points to this.
Reported in 1 NHTSA complaint - 3
Faulty Ignition Coils
Medium severityA weak or failing ignition coil will fail to ignite the air/fuel mixture properly, leading to a misfire. Swap the suspected coil to another cylinder to see if the misfire follows.
Common cause - 4
Worn or Fouled Spark Plugs
Low severitySpark plugs degrade over time, increasing the gap or becoming fouled with carbon/oil, which prevents a strong spark. Inspect spark plugs for wear, improper gap, or fouling.
Common cause - 5
Vacuum Leaks / Intake Manifold Issues
Medium severityUnmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires. Check for cracked hoses, leaking intake gaskets, or listen for a hissing sound.
Common cause - 6
Fuel Delivery Issues (Injectors or Pump)
Medium severityClogged fuel injectors or low fuel pressure can starve the engine of fuel, leading to a lean misfire. Test fuel pressure and perform an injector balance test.
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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