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P0300 Random/Multiple Cylinder Misfire Detected

The engine is misfiring, but the computer can't pin it to one cylinder — either it's wandering between cylinders or several are misfiring at once.

Misfire & ignition

The ECU watches crankshaft speed between firing events. A cylinder that fails to burn its charge lets the crank slow for an instant, and the ECU counts those stumbles. P0300 means it counted enough of them to trip the light but couldn't isolate a single cylinder. That distinction matters: a P0301 points at one cylinder's parts, while P0300 points at something the whole engine shares — fuel, air, spark timing, or compression across the board.

Diagnose P0300 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you need

Can I keep driving?

Driveable

If the light is flashing, stop driving and get it towed or fixed — that flash specifically means converter-damaging misfire. If the light is steady, short low-load trips are usually survivable, but fix it soon.

How serious

Moderate to high. Raw unburned fuel dumped into the exhaust overheats the catalytic converter, and a converter is a far more expensive part than whatever caused the misfire. A flashing check-engine light means damage is happening right now.

Symptoms you'll notice

What causes P0300

Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.

01

Worn or fouled spark plugs

The single most common cause, and the first thing to rule out. Plugs wear their gap open gradually, so misfire arrives slowly rather than all at once. If nobody can produce a receipt for plugs in the last 60–100k miles, start here — it's the cheapest test in the list and it doubles as maintenance.

02

Vacuum leak

Unmetered air entering after the mass airflow sensor leans out every cylinder at once, which is exactly the all-cylinder pattern P0300 describes. Cracked intake boots, brittle PCV hoses, a leaking intake manifold gasket. Very often paired with P0171 — seeing both together is a strong vacuum-leak signature.

03

Failing ignition coils

On coil-on-plug engines each cylinder has its own coil, so several weak ones — common once they're all the same age — reads as a random misfire rather than a single-cylinder one.

04

Low fuel pressure

A tired fuel pump or a clogged filter starves every cylinder together. The tell is that the misfire appears under load or hard acceleration and cleans up at idle, where demand is low.

05

Clogged or leaking fuel injectors

Deposits narrow the spray pattern across the whole rail. More likely on high-mileage direct-injection engines and on cars that live on short trips.

06

EGR valve stuck open

Exhaust gas recirculating at idle displaces the air/fuel the cylinders need. Usually worst at idle and light throttle, and often sets an EGR code alongside.

07

Low compression or jumped timing

The expensive end of the list: a stretched timing chain, worn rings, or burnt valves. Check this last, after the cheap causes are eliminated — but if a compression test comes back low, no amount of plugs and coils will fix it.

How to diagnose it

  1. Read the freeze-frame data stored with the code — engine temp, RPM and load at the moment it set tell you whether this is a cold-start, idle, or under-load misfire, which cuts the cause list in half.
  2. Pull the spark plugs and read them. Even wear across all of them suggests age; one oil-soaked or fuel-washed plug redirects you to a single-cylinder fault.
  3. Check live fuel-trim data. Both short- and long-term trims strongly positive means the engine is running lean — chase a vacuum leak or fuel delivery.
  4. Listen for a vacuum leak with the engine idling, or smoke-test the intake if you have access to a smoke machine.
  5. Test fuel pressure at the rail against the manufacturer's spec, both at idle and with the throttle snapped open.
  6. If everything above is clean, run a compression test. This is the step that tells you whether to keep buying parts or stop.

Parts you might need

Tools for the job

Related trouble codes

Get the parts list for your vehicle Ranked causes, tutorials and live part prices for your exact year, make and model

Fitment matters. Causes and parts above are the common cases for P0300 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.