P0300: Random/Multiple Cylinder Misfire Detected
Quick answer
P0300 is the standardised OBD-II code for random/Multiple Cylinder Misfire Detected. The computer counts tiny fluctuations in crankshaft speed between each firing event and uses them to detect when a cylinder fails to fire cleanly. The most likely cause is worn spark plugs across multiple cylinders, not the most expensive one. Keep any driving short and light until it is repaired.
Severity 3 of 4. Short trips only.
Fix now · Short trips only
| Code | P0300 |
|---|---|
| Standard name | Random/Multiple Cylinder Misfire Detected |
| System | Misfire and ignition |
| Subsystem | Ignition and combustion |
| Sets the | Misfire monitor |
| Severity | Fix now (3 of 4) |
| Safe to drive | Short trips only |
| Tool needed | Scanner with live data |
| Cause | How often | What to check |
|---|---|---|
| Worn spark plugs across multiple cylinders | Most likely | Plugs wear out together on roughly the same schedule, so several failing near the same mileage is common. |
| Vacuum leak in a shared intake hose or gasket | Common | Unmetered air entering after the mass airflow sensor leans out every cylinder at once. |
| Low fuel pressure from a weak fuel pump | Worth checking | A pump that cannot keep up with demand starves every cylinder under load, not just one. |
| Contaminated or old fuel | Less common | Water or stale fuel affects combustion in every cylinder equally. |
| Failed ignition coil pack shared by multiple cylinders | Uncommon | Some engines use one coil pack to fire two or more cylinders, so one coil failure looks like a random multi-cylinder misfire. |
| Clogged catalytic converter causing high exhaust backpressure | Rare | Severe backpressure can choke combustion enough to register as misfire across cylinders. |
TOPDON TopScan Lite OBD2 Scanner, Bidirectional Scan Tool, 8 Resets & AI
Adds live sensor streams and freeze frame, which is what turns a code into a diagnosis rather than a guess.
Coverage varies by tool and by model year, so check a specific tool against a specific vehicle before buying.
What P0300 tells you, and what it does not
The computer counts tiny fluctuations in crankshaft speed between each firing event and uses them to detect when a cylinder fails to fire cleanly. This code sets when those misfire events are spread across multiple cylinders rather than concentrated on one, which points to a cause that affects the whole engine instead of a single spark plug or injector. A random misfire is often a fuel, air or ignition supply problem shared by every cylinder.
The code sits in the ignition and combustion area and is reported by the misfire monitor. It names the circuit or the condition where the computer saw a reading outside its expected range. It does not name a failed part, and several genuinely different faults set this same code, which is the whole reason the causes below are ordered rather than listed.
What people usually notice
- Engine shaking at idle
- Flashing or steady check engine light
- Hesitation under load
- Rough idle
- Noticeable loss of power
What causes P0300?
The causes below are ordered by how often they turn out to be the answer, cheapest and most common first. That order matters more than the list itself: the expensive component named in the code text is very rarely the first thing to replace, and working down from the top is what stops a ignition and combustion fault becoming an expensive guess.
Worn spark plugs across multiple cylinders is the one to rule out before anything else. Plugs wear out together on roughly the same schedule, so several failing near the same mileage is common.
Working out which cause it is
Start with freeze frame. Engine load and RPM at the fault show whether the misfire happens at idle, cruise or under acceleration. That snapshot is taken at the instant the code set, and it is the single most useful piece of evidence you have, which is also why clearing the code before reading it is such a costly habit.
This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live misfire counters broken out by cylinder show whether the misfire is truly random or actually concentrated on one or two cylinders.
The order worth working in
- 1. Worn spark plugs across multiple cylinders: Plugs wear out together on roughly the same schedule, so several failing near the same mileage is common.
- 2. Vacuum leak in a shared intake hose or gasket: Unmetered air entering after the mass airflow sensor leans out every cylinder at once.
- 3. Low fuel pressure from a weak fuel pump: A pump that cannot keep up with demand starves every cylinder under load, not just one.
- 4. Contaminated or old fuel: Water or stale fuel affects combustion in every cylinder equally.
- 5. Failed ignition coil pack shared by multiple cylinders: Some engines use one coil pack to fire two or more cylinders, so one coil failure looks like a random multi-cylinder misfire.
- 6. Clogged catalytic converter causing high exhaust backpressure: Severe backpressure can choke combustion enough to register as misfire across cylinders.
What P0300 means for driving the car
Short trips only, since a misfire severe enough to flash the check engine light genuinely damages the catalytic converter within minutes.
This is a severity 3 of 4 code, which means continuing to drive normally risks damage that costs considerably more than the repair in front of you. Treat the lamp as an instruction rather than a notification.
What does it cost to ignore P0300?
Unburned fuel from ongoing misfires overheats and destroys the catalytic converter, turning a spark plug or vacuum leak repair into a much more expensive exhaust repair.
There is also the diagnostic cost of waiting. Freeze frame data, pending code history and the readiness monitor state all describe the fault as it was when it set, and all of it is lost the moment somebody clears the code to make the lamp go out.
P0300 by make
Tools that can diagnose P0300
Adds live sensor streams and freeze frame, which is what turns a code into a diagnosis rather than a guess.
- LJPXHHU
OBD2 Bluetooth Scanner Car Code Reader for iOS, Android and Windows
- wireless
$13.98 Check pricePrices change often - Veepeak
Veepeak Mini Bluetooth OBD2 Scanner Code Reader for Android (NOT for iOS)
- wireless
$14.99 Check pricePrices change often - MOCATEC
WiFi ELM327 OBD2 Adapter WiFi ELM 327 OBD Scanner for Universal 12V Vehicle
- wireless
$15.95 Check pricePrices change often - UMEIJA
OBD2 Scanner Diagnostic Tool, Car Scanner for iOS & Android, Bluetooth 5.4
- wireless
$29.99 Check pricePrices change often
Common questions
What does code P0300 mean?
P0300 is the generic OBD-II code for random/Multiple Cylinder Misfire Detected. The computer counts tiny fluctuations in crankshaft speed between each firing event and uses them to detect when a cylinder fails to fire cleanly. This code sets when those misfire events are spread across multiple cylinders rather than concentrated on one, which points to a cause that affects the whole engine instead of a single spark plug or injector. A random misfire is often a fuel, air or ignition supply problem shared by every cylinder. It is a standardised definition, so it means the same thing on every manufacturer, although the fault behind it differs from car to car.
Can I drive with P0300?
Short trips only, since a misfire severe enough to flash the check engine light genuinely damages the catalytic converter within minutes. On the severity scale this sits at 3 of 4, described as fix now. Whatever the code, a check engine light that starts flashing changes the answer immediately: that means an active misfire and the correct response is to reduce load and stop driving.
What is the most common cause of P0300?
Worn spark plugs across multiple cylinders is the cause worth ruling out first. Plugs wear out together on roughly the same schedule, so several failing near the same mileage is common. Work down the ordered list rather than replacing the component named in the code text, because that component is the expensive answer and it is rarely the right one.
Will P0300 clear itself?
If the underlying fault genuinely goes away, the computer turns the lamp off after the monitor passes on a number of consecutive drive cycles, and the code moves to history before ageing out. A code that clears and returns is not fixed, it is intermittent. Clearing it manually erases the freeze frame data and resets every readiness monitor to incomplete.
What scanner do I need for P0300?
This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live misfire counters broken out by cylinder show whether the misfire is truly random or actually concentrated on one or two cylinders. Vehicle coverage still varies by tool and by model year, so check a specific tool against a specific vehicle rather than assuming a capability tier guarantees access.