Ignition & misfire · Powertrain · generic (SAE-defined)
P0300: Random/Multiple Cylinder Misfire Detected
P0300 means the engine computer detected misfires that are not limited to one cylinder, either moving randomly between cylinders or occurring in several at once.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0300 sets
The powertrain control module (PCM) watches the crankshaft position sensor for tiny changes in crankshaft speed. When a cylinder fails to fire, the crankshaft briefly slows, and the PCM counts these events over a set number of revolutions. If the misfire rate is high enough to raise emissions or threaten the catalytic converter, and the misfires are spread across cylinders rather than isolated to one, P0300 sets, often alongside individual cylinder codes. Misfire counts and monitoring windows are manufacturer-specific.
Common causes of P0300
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Vacuum leak from a cracked hose, intake gasket, or positive crankcase ventilation (PCV) system
- Low fuel pressure from a weak pump, clogged filter, or failing regulator
- Worn spark plugs or failing ignition coils on multiple cylinders
- Dirty or failing mass air flow (MAF) sensor causing a lean mixture
- Contaminated or low-quality fuel, including water in the fuel
- Exhaust gas recirculation (EGR) valve stuck open
- Low compression from a head gasket leak, burnt valve, or jumped timing chain/belt
- Crankshaft or camshaft position sensor signal problems
P0300 symptoms
- Check engine light steady or flashing
- Rough idle, shaking, or vibration
- Hesitation, stumbling, or loss of power when accelerating
- Poor fuel economy
- Fuel or rotten-egg smell from the exhaust
- Hard starting or stalling in some cases
How P0300 is diagnosed
- Record freeze frame data, including rpm, load, coolant temperature, and fuel trims, to see when the misfire occurs.
- Check for companion codes such as P0171/P0174 (lean), fuel pressure, or position sensor codes that point to a common cause.
- View misfire counters for each cylinder on a scan tool to see which cylinders are affected and when.
- Inspect for vacuum leaks with a smoke test and check fuel trims; high positive trims suggest a lean condition.
- Test fuel pressure and volume against specification.
- Inspect spark plugs and test coils, swapping a coil between cylinders to see if the misfire follows it.
- Run compression or leak-down tests if ignition and fuel checks pass.
Typical fixes for P0300
- Repair vacuum or intake leaks
- Replace worn spark plugs and failed ignition coils or plug wires
- Clean or replace the MAF sensor
- Replace the fuel pump, filter, or pressure regulator
- Repair a stuck-open EGR valve
- Repair mechanical faults such as a head gasket, valve, or timing component
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0300 FAQ
What does code P0300 mean?
P0300 means the engine computer detected misfires that are not limited to one cylinder, either moving randomly between cylinders or occurring in several at once. The standard definition is "Random/Multiple Cylinder Misfire Detected."
Can I drive with a P0300 code?
If the check engine light is steady and the engine runs reasonably smoothly, short, gentle trips to a repair shop are usually acceptable. If the light is flashing, the misfire is severe enough to damage the catalytic converter, so reduce speed and load, pull over when safe, and stop driving soon; towing is the safer choice.
What is the difference between a steady and a flashing check engine light with P0300?
A steady light means a fault was detected and should be fixed soon. A flashing light means the misfire is happening right now at a rate that can overheat and damage the catalytic converter, so driving should stop as soon as it is safe.
Why does P0300 not tell me which cylinder is misfiring?
P0300 is set when misfires are spread across cylinders or the computer cannot pin them to one. Cylinder-specific codes such as P0301 to P0308 often appear alongside it, and the scan tool misfire counters can show which cylinders are affected.
Can bad gas cause P0300?
Yes. Water-contaminated or very low-octane fuel can cause misfires across all cylinders. If the code appeared right after a fill-up, fuel quality is worth considering, but vacuum leaks and ignition wear remain more common causes.
Keep researching
Engine guides by brand (known issues, specs)
More ignition & misfire codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.