P0300: Random/Multiple Cylinder Misfire Detected

What it means

The ECU has detected misfires that are not concentrated on a single cylinder. The misfire monitor measures crankshaft acceleration after each combustion event; missing acceleration on multiple cylinders, or randomly across cylinders, triggers this code.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The engine control module estimates whether each combustion event produced the expected crankshaft acceleration. P0300 sets when the misfire monitor detects misfires across multiple cylinders or at changing cylinders, rather than repeatedly identifying just one cylinder.

Common causes

Most likely first.

1. Worn spark plugs
2. Vacuum leak affecting all cylinders
3. Fuel pressure low
4. Timing chain stretched (high mileage)

Symptoms

• Check engine light on or flashing
• Rough idle and uneven running
• Power loss, hesitation under acceleration
• Increased fuel consumption
• Possible smell of unburned fuel from exhaust

How to diagnose it

1. Read freeze-frame data and cylinder misfire counters to see when misfires occur and whether they affect several cylinders.
2. Inspect spark plugs across the engine for wear, fouling, or damage, since a shared pattern can point to a maintenance issue.
3. Check intake and PCV hoses and connections for leaks that could admit unmetered air to multiple cylinders.
4. Compare fuel trims and measure fuel pressure against the manufacturer's specification to check for a lean mixture or weak fuel supply.
5. If the misfires persist, assess mechanical timing and engine condition using the manufacturer's diagnostic procedures.

Common fixes

• Replace worn or fouled spark plugs.
• Repair leaking intake or PCV hoses and seals.
• Restore fuel pressure to the manufacturer's specification.
• Repair a stretched timing chain if mechanical timing checks confirm it.

Can I keep driving?

If the check engine light is flashing, avoid driving and arrange prompt repair because ongoing misfires can overheat and damage the catalytic converter. With a steady light and mild symptoms, keep trips short and avoid hard acceleration; stop if the engine runs very roughly or loses power.