P0300 on a 2020 Ram 1500
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 Ram 1500
Ranked from 613 NHTSA owner complaints filed for this vehicle.
- 1
Head gasket failure letting coolant into a cylinder
High severityOne owner had all four head gaskets crack, sending coolant into the engine, depleting the coolant, and causing repeated overheating/breakdowns — a mechanism that also fouls a cylinder enough to misfire.
Reported in 1 NHTSA complaintParts:head gasket - 2
Crankshaft position sensor / reluctor wheel fault
Medium severityOne owner's truck threw code P0336 (crank sensor/reluctor wheel) along with loss of power and limp mode — a bad crank signal disrupts spark/fuel timing and can register as a misfire.
Reported in 1 NHTSA complaint - 3
Weak or failing fuel pump (including EcoDiesel HPFP recall)
Medium severityOne EcoDiesel owner was mid-recall for the high-pressure fuel pump, a component whose failure causes stalling/rough running that can present alongside misfire-type codes.
Reported in 1 NHTSA complaintParts:fuel pump - 4
Worn or fouled spark plugs
Medium severityStill the leading real-world cause of a random misfire code on any gas engine, including the 5.7L HEMI.
Common causeParts:spark plug - 5
Failing ignition coil(s)
Medium severityA weakening coil drops spark energy on its cylinder, often worse under load or when hot.
Common causeParts:ignition coil - 6
Clogged or leaking fuel injector(s)
Medium severityA partially clogged or dribbling injector starves or floods a cylinder, producing a repeatable misfire.
Common causeParts:fuel injector - 7
Vacuum or intake air leak
Medium severityUnmetered air leaning out a cylinder is a common misfire contributor, especially at idle.
Common cause - 8
Carbon-fouled intake valves or low cylinder compression
Low severityCarbon buildup or worn rings/valves reduce a cylinder's ability to seal and burn fuel cleanly, causing a chronic 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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