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P0300

P0300 on a 2021 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 2021 Ram 1500

Ranked from 659 NHTSA owner complaints filed for this vehicle.

Sort by:
  1. 1

    Worn/failed valvetrain component (camshaft lobe or lifter) causing cylinder-specific misfire

    High severity

    One complaint documents flattened cam lobes from a failed lifter plus a hairline cylinder-wall crack letting coolant bleed in, producing a persistent multi-cylinder misfire that required an engine rebuild.

    Reported in 1 NHTSA complaint
    Parts:valve liftercamshaft
  2. 2

    EGR cooler bypass control failure

    Medium severity

    One complaint describes the EGR cooler bypass control breaking on this generation of truck; a stuck or failed EGR bypass can upset combustion enough to trigger random misfire.

    Reported in 1 NHTSA complaint
    Parts:EGR cooler
  3. 3

    Worn or fouled spark plugs

    Low severity

    Aged, gapped-out, or fouled plugs are the single most common cause of random/multiple-cylinder misfire; check plug condition and gap against spec.

    Common cause
    Parts:spark plug
  4. 4

    Failing ignition coil(s)

    Medium severity

    A weak or intermittently-arcing coil produces a misfire that a scan tool will usually pin to one cylinder; swap-test coils between cylinders to confirm.

    Common cause
    Parts:ignition coil
  5. 5

    Clogged or leaking fuel injector

    Medium severity

    A restricted or dribbling injector starves or over-fuels a cylinder; injector balance/flow test isolates the culprit.

    Common cause
    Parts:fuel injector
  6. 6

    Vacuum or intake leak

    Medium severity

    Unmetered air entering downstream of the throttle leans out one or more cylinders enough to misfire; smoke-test the intake for leaks.

    Common cause
  7. 7

    Carbon-fouled intake valves

    Low severity

    Direct-injected engines build carbon on the backs of the intake valves over time, disrupting airflow/atomization enough to cause a rough-running misfire; a borescope inspection confirms.

    Common cause
  8. 8

    Low compression from worn piston rings or valves

    High severity

    General mechanical wear reduces a cylinder's ability to seal and fire cleanly; a compression or leak-down test isolates the affected cylinder.

    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

1

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.

2

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.

3

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.

4

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.

5

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 RoughFlashing Check Engine Light