Can you keep driving?
Can you keep driving?
Stop driving if any of these apply
- !The check-engine light is flashing.
- !The engine is running badly enough that traffic safety or engine damage becomes a concern.
What to check first
Step-by-step checks
- 1
Safety first
If the check-engine light is flashing or the engine is shaking badly, stop driving before you inspect anything else
- 2
Free - no tools
Check for other codes that point to a lean condition, coil fault, or cylinder-specific misfire
- 3
Basic tool needed
Look for obvious vacuum leaks, loose connectors, or anything recently left unplugged in the engine bay
- 4
Basic tool needed
If scan data is available, compare misfire counts and fuel trims before buying parts
- 5
Basic tool needed
If the engine is missing mainly at idle or under load, note that pattern before moving to the next step
If the code returns
- -If the code appears with a lean code, look harder for unmetered air or a fuel-delivery problem.
- -If the fault is strongest under load, ignition parts and fuel supply move higher on the list.
- -If the code returns immediately after clearing, focus on the active fault rather than the stored history.
Background
What this code means
P0300 is a generic OBD-II random misfire code.
It usually means the misfire pattern is spread across more than one cylinder, so the cause can be ignition, air, fuel, or sometimes a mechanical issue rather than a single bad plug.
Diagnosis
Common causes
Ignition weakness
Worn spark plugs, weak coils, or poor coil connections are among the most common first checks.
Vacuum leak
A split hose or intake leak can create a lean spot that shows up as a random misfire.
Fuel delivery issue
Low fuel pressure or a clogged injector can leave more than one cylinder short of fuel.
Mechanical fault
Low compression or valve sealing issues can cause a persistent misfire pattern.
Avoid these mistakes
What not to do
- xDo not replace major parts before checking the simple causes first.
- xDo not ignore a flashing check-engine light or obvious drivability symptoms.
Parts
Parts that may need replacing
See also
Related OBD codes
Source notes
Generic OBD-II (SAE J1979 / ISO 15031-5). P0300 was expanded around common random misfire patterns, with conservative guidance focused on ignition, air, fuel, and compression checks.
- -A random misfire code is a diagnosis starting point, not a guaranteed parts answer.
This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.
This is generic OBD-II guidance and should not override vehicle-specific service information. Some makes have model-specific misfire patterns, service bulletins, or coil-plug test procedures that should be checked before ordering parts.
Last reviewed: 2026-04-10