P0300 on a 2019 Ram 1500 Classic
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 Ram 1500 Classic
Ranked from 1,453 NHTSA owner complaints filed for this vehicle.
- 1
5.7L Hemi camshaft/lifter (MDS roller lifter) failure shedding metal into the valvetrain
High severityMultiple owners report camshaft/lifter failure and metal shavings on the VVT sprocket; one dealer inspection found cylinder 6 misfiring directly tied to a worn lifter/VVT condition.
Reported in 2 NHTSA complaints - 2
Low compression from worn engine internals (rings/valves)
High severityAn independent mechanic recommended full engine replacement after rough idling, shaking, and an inability to exceed 30 MPH — consistent with a mechanically-worn cylinder rather than an ignition/fuel fault.
Reported in 1 NHTSA complaintParts:piston rings - 3
EGR cooler/valve fault dumping excess exhaust gas into a cylinder
Medium severityA failed EGR cooler that leaked onto the intake manifold was reported; a stuck-open EGR passage can dilute the charge on affected cylinders enough to misfire.
Reported in 1 NHTSA complaintParts:EGR cooler - 4
Worn or fouled spark plugs
Low severityClassic top cause of random/multiple-cylinder misfire; check gap wear, electrode erosion, or oil/carbon fouling.
Common causeParts:spark plugs - 5
Failing ignition coil(s)
Medium severityWeak or intermittently-failing coils drop spark energy on one or more cylinders, especially under load or heat soak.
Common causeParts:ignition coil - 6
Clogged or leaking fuel injectors
Medium severityUneven fuel delivery from a dirty or leaking injector produces a lean, misfiring cylinder; check injector balance/spray pattern.
Common causeParts:fuel injector - 7
Vacuum or intake leaks
Medium severityUnmetered air entering downstream of the MAF leans out one or more cylinders enough to misfire, especially at idle.
Common cause - 8
Carbon-fouled intake valves
Low severityDirect-injection Hemi engines accumulate carbon on the backs of intake valves over time, disrupting airflow/atomization on individual cylinders.
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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