P0300

P0300: Random/Multiple Cylinder Misfire Detected

What P0300 means

P0300 is “Random/Multiple Cylinder Misfire Detected.” Unlike codes P0301–P0308 (which point at one specific cylinder), P0300 means the engine’s computer saw the crankshaft’s rotational speed fluctuating in a way that doesn’t line up with any single cylinder — combustion isn’t happening cleanly across multiple cylinders, or it’s rotating between which cylinder misfires each time. Any of those looks the same to the computer: inconsistent power production it can’t localize.

Common causes

Ignition-system components are the single most common starting point: worn spark plugs and failing ignition coils account for a large share of P0300 diagnoses on their own. Beyond ignition, common causes include:

Because the code is “random/multiple” rather than cylinder-specific, the underlying cause is often something that affects the whole engine (a vacuum leak, fuel pressure) rather than one bad component on one cylinder — that’s a useful diagnostic starting point, not a certainty.

DIY-fixable, or shop repair?

Partially DIY-fixable. Spark plugs and, on many vehicles, ignition coils are within reach of a home mechanic with basic tools and the vehicle’s service manual. Vacuum leak tracing, fuel pressure testing, and compression testing generally need shop equipment (a smoke machine, a fuel pressure gauge, a compression tester) most owners don’t have on hand.

Typical cost range

Simple repairs like spark plug replacement often run around $100 in parts, while more involved fixes (a vacuum leak repair, or replacing multiple ignition coils) commonly land in the $300–$1,000 range depending on labor rates and how many components need replacing. Most shops also charge a separate diagnostic fee (roughly $100–$180) to actually identify which of the causes above applies before quoting a repair.

Don’t ignore this code. A sustained misfire can damage the catalytic converter (unburned fuel reaching it) and, over time, the engine itself — this is one of the check-engine-light codes worth addressing promptly rather than waiting.