P0300 code meaning
Random/Multiple Cylinder Misfire Detected
Powertrain system Generic code P03xx codes Check engine light
What P0300 means
The engine module detects misfire from crankshaft speed: a cylinder that does not fire gives no acceleration impulse. At a catalyst-damaging rate (CARB: at least 5 % per 200 revolutions) the warning light flashes; at an emissions-relevant rate (at least 1 % per 1,000 revolutions – GM about 2–5 %, Ford 0.9–1.5 %) it comes on after two trips. Ford and GM may shut off a misfiring cylinder's injector to protect the catalyst. P0300 sets when the misfire cannot be assigned to one cylinder: several cylinders each account for more than 10 %, the cylinder changes randomly, or – at Ford – the cylinder cannot be identified at high speed. It often appears together with cylinder codes. Causes are usually systemic: false air, worn plugs on several cylinders, fuel pressure or fuel quality, valve timing – and false detection from a damaged tone wheel, rough roads or vibration. Bulletins name coils, cracked plug insulators and wrong plug gaps.
P0300 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 6 hours
- Clears after repairAfter a drive cycle
Symptoms of P0300
- Check engine light on, flashing at a catalyst-damaging rate
- Rough idle, jerking, vibration
- Loss of power, hesitation
- Smell of unburnt fuel, higher consumption
Common causes of P0300
- Most likelyFalse air (vacuum leak, crankcase ventilation, intake gasket)
- Most likelyWorn or wrong spark plugs on several cylinders, faulty ignition coils
- PossibleFuel pressure too low or high, contaminated fuel
- Less likelyValve timing (stretched chain), valves, compression on several cylinders
- Less likelyFalse detection: tone wheel or pulley, rough road, vibration, software
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ignition systemFuel systemIntake systemCrankshaft position sensor
What each part of P0300 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3 | Area: ignition system or misfire. |
| 00 | The exact fault in that area. |
What to do next
- Note P0300 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0300
What does P0300 mean?
P0300 means "Random/Multiple Cylinder Misfire Detected". The engine module detects misfire from crankshaft speed: a cylinder that does not fire gives no acceleration impulse. It is a generic code, so it means the same on every make.
Is it safe to drive with P0300?
Drive gently and only to a workshop. With P0300 the car can go into limp mode (reduced power) to protect itself.
Will P0300 fail an emissions test?
Yes, it can. P0300 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0300 to fix?
Difficulty: medium. A typical repair takes 0.5 to 6 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0300 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.