The most common causes are: Worn spark plugs (the single most common cause); Failing ignition coils or coil packs; Vacuum leak affecting the whole intake; Low fuel pressure from a weak pump or clogged filter; Clogged or dirty fuel injectors.

How much does it cost to fix P0300?

Typical repairs range from $100–$350 for replace spark plugs up to $1,500+ for major engine repair (compression loss). Costs vary by vehicle and region.

P0300powertrain

P0300 – Random/Multiple Cylinder Misfire Detected

What does P0300 mean?

The engine computer has detected misfires occurring randomly across multiple cylinders, rather than in one specific cylinder. A misfire means a cylinder failed to produce its expected power stroke. Because it is random rather than isolated, the cause is usually something shared by all cylinders — ignition, fuel delivery, or air.

What causes P0300?

Listed from most to least common:

1Worn spark plugs (the single most common cause)
2Failing ignition coils or coil packs
3Vacuum leak affecting the whole intake
4Low fuel pressure from a weak pump or clogged filter
5Clogged or dirty fuel injectors
6Worn distributor cap and rotor on older vehicles
7Failing crankshaft or camshaft position sensor
8Low engine compression from worn rings or valves
9EGR valve stuck open

Code breakdown

SystemP — Powertrain

TypeGeneric (standardized SAE / OBD-II code — same meaning across most manufacturers)

SubsystemIgnition system or misfire

Common symptoms

Check engine light on, or flashing during active misfire
Rough idle and noticeable vibration
Hesitation, stumbling, or jerking under acceleration
Loss of power
Increased fuel consumption
Engine may be hard to start

How to diagnose

1Check for accompanying cylinder-specific codes (P0301–P0308). Their presence narrows the search considerably.
2If the check engine light is flashing, stop driving to protect the catalytic converter.
3Inspect spark plugs — look for wear, incorrect gap, cracks, or fouling. Replace if beyond service interval.
4Test ignition coils, or swap a coil to a different cylinder and see whether the misfire follows it.
5Smoke-test the intake for vacuum leaks.
6Check fuel pressure against specification.
7Run a compression test if ignition and fuel check out — this reveals mechanical problems.

Persistent misfires dump unburned fuel into the exhaust and can destroy the catalytic converter quickly. If the check engine light is flashing, stop driving and have the vehicle towed — that indicates a misfire severe enough to cause immediate damage.

Common fixes and estimated costs

Repair	Estimated cost
Replace spark plugs	$100–$350
Replace ignition coil(s)	$150–$600
Replace spark plug wires	$80–$250
Clean or replace fuel injectors	$200–$900
Repair vacuum leak	$50–$400
Major engine repair (compression loss)	$1,500+

Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.

Good to know

A flashing check engine light with P0300 is the one situation where you should stop driving immediately — raw fuel reaching a hot catalytic converter can destroy it within minutes. Start diagnosis with spark plugs and coils; together they account for the majority of cases.

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This information is provided for general reference only and may vary by manufacturer, model, and year. It is not a substitute for professional diagnosis or repair.