P0300 on a 2021 Ram 1500 Crew Cab Trx

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 2021 Ram 1500 Crew Cab Trx

Ranked from 659 NHTSA owner complaints filed for this vehicle.

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1
Worn/collapsed valve lifter and camshaft lobe wear
High severity
One complaint documents a confirmed misfire and stall traced to flattened cam lobes from a failed lifter — direct mechanical loss of a cylinder's valve event.
Reported in 1 NHTSA complaint
Parts:valve lifters camshaft
2
Oil-starvation valvetrain damage from an oil-gallery bolt backing out
High severity
A reported case of oil gallery bolts loosening starved the rocker/cam area of oil, chewing up the cam and rockers — the same wear pattern that produces a misfire.
Reported in 1 NHTSA complaint
3
Failing high-pressure fuel pump causing fuel-starvation misfire
Medium severity
Several of these trucks stalled and were later found to have a failing/recalled high-pressure fuel pump; inadequate fuel pressure under load will misfire cylinders before it fully stalls the engine.
Reported in 1 NHTSA complaint
Parts:high-pressure fuel pump
4
Worn or fouled spark plugs
Low severity
Classic first-check for random misfire; inspect gap and electrode wear, especially past the recommended replacement interval.
Common cause
Parts:spark plugs
5
Failing ignition coil(s)
Medium severity
A coil breaking down under load drops a cylinder intermittently; swap-test the coil to the misfiring cylinder to confirm.
Common cause
Parts:ignition coil
6
Clogged or leaking fuel injector(s)
Medium severity
An injector delivering too little (clogged) or dribbling (leaking) fuel disrupts combustion on that cylinder; injector balance/flow test will isolate it.
Common cause
Parts:fuel injector
7
Vacuum or intake leak
Medium severity
Unmetered air entering after the MAF leans out individual cylinders enough to misfire, especially at idle; smoke-test the intake tract and gaskets.
Common cause
8
EGR valve/passage fault
Low severity
A stuck-open EGR dumps excess exhaust gas into the intake charge, diluting combustion at idle/light load and triggering random misfire.
Common cause
Parts: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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Matching symptoms

Car Runs Rough Flashing Check Engine Light