P0300 (random or multiple misfire): what it means and whether you can drive
What does P0300 mean?
P0300 is the generic code for "Random/Multiple Cylinder Misfire Detected", Volkswagen's wording (VW TSB 01-16-13, 2022). Honda and Mazda call it "random misfire detected" (Honda 18-025; Mazda 01-006/18). A misfire is a cylinder firing cycle in which the fuel doesn't burn properly, so that cylinder adds little or no power.
- P0301 to P0308 are the cylinder-specific codes: cylinder 1 misfire, cylinder 2 misfire, and so on.
- P0300 means the misfire isn't confined to one cylinder, or the computer can't tell which cylinder it is.
California's OBD-II regulation sets the rules (13 CCR § 1968.2, section (e)(3.1)):
- The car must identify the misfiring cylinder where it can. A manufacturer may get approval to store a general misfire code under conditions in which the cylinder can't be reliably identified.
- When more than one cylinder misfires, a separate multiple-cylinder code is stored.
- From the 2005 model year, if more than 90% of the misfires are in one cylinder, the car may store that cylinder's code instead. If two or more cylinders each have more than 10% of the misfires, it must store the multiple-cylinder code.
Scope. That regulation covers 2004 and newer vehicles certified for California. The California Air Resources Board (CARB) says that in practice virtually all vehicles sold in the US are designed and certified to its OBD II requirements. We have not checked other countries' rules.
How does the car detect a misfire?
One established method watches the crankshaft. A Ford patent explains the idea: a cylinder that fires properly speeds the crankshaft up on its power stroke, while a misfiring one lets it slow down. The engine computer measures those tiny speed changes between firings with sensors the engine already has (Ford patent US5044194A). The same patent notes that bumps and potholes can disturb those measurements. California's rule, for its part, lets manufacturers pause misfire detection on rough roads.
The regulation then sets two levels of misfire, each as a percentage of firings (13 CCR § 1968.2, (e)(3.2)):
| Level | How it's measured | Threshold |
|---|---|---|
| Catalyst-damaging misfire | Every 200 crankshaft revolutions, at each engine speed and load | Whatever rate the manufacturer finds would heat the catalyst enough to damage it (it may use 5% where its own figure is lower) |
| Emissions misfire | Every 1,000 revolutions | The rate that would push emissions over a set limit (1.5 times the standard on vehicles not certified to California's LEV III standards); the manufacturer may use 1% where its own figure is lower |
Why the converter matters: the Ford patent says a misfire passes unburned fuel to the catalytic converter "where it will burn, thereby increasing the temperature in the catalytic converter and leading to its destruction."
The regulation also lets manufacturers, with CARB's approval, switch the misfire monitor off in conditions that could fool it ((e)(3.3.4)). These include rough roads, traction control activity, a fuel level of 15% or less of the tank's capacity, and a coolant temperature below −6.7 °C (20 °F). If the coolant is below −6.7 °C (20 °F) at start, the monitor can stay off until the coolant passes 21.1 °C (70 °F).
Steady or flashing: what the light is telling you
| What you see | What the regulation says is happening | Source |
|---|---|---|
| Flashing light | Misfire at the catalyst-damaging level. A pending code is stored as soon as that level is exceeded (three times in one drive at the speeds and loads of the federal emissions test cycle, or once outside them), and the light blinks once per second while the misfire continues. It may stop flashing when the misfire stops | 13 CCR § 1968.2 (e)(3.4.1) |
| Steady light after flashing | The misfire came back on a later drive (the next one, or the next with similar conditions), a confirmed code was stored, and the light stays on after the misfiring ceases | same |
| Steady light, no flashing | Usually the lower emissions level. A pending code is stored after the fourth time the threshold is crossed in one drive (the first time, if it happens in the first 1,000 revolutions after start), and the light comes on if it happens again on the next drive or the next one with similar conditions | 13 CCR § 1968.2 (e)(3.4.2) |
A steady light doesn't always mean a mild misfire. The regulation lets cars that cut fuel to the misfiring cylinder, to prevent overfueling, keep the light steady instead of flashing (13 CCR § 1968.2, (e)(3.4.1)(D)). A manufacturer may also get approval for a steady light during extreme misfire at all speeds and loads. So if the engine shakes, stumbles or loses power, treat a steady light as seriously as a flashing one (our inference).
Can you keep driving with P0300?
If the light is flashing, plan to stop soon. CARB says a blinking light means a malfunction that could be damaging your catalytic converter, and many manufacturers recommend service as soon as possible (CARB). The owner's manuals go further:
- GM (2025 Chevrolet Equinox): reduce speed, avoid hard acceleration and uphill grades, and cut any trailer load. If it keeps flashing, park somewhere safe, turn the vehicle off, wait at least 10 seconds and restart. If it still flashes, see a dealer as soon as possible.
- Honda (2019 Fit owner's guide): a blinking light means a misfire has been detected. "Stop in a safe place and wait for the engine to cool down."
Follow your own manual. When in doubt, treat a flashing light as "get off the road soon, gently," not "finish the trip".
Stop now if the engine shakes badly or loses power, or if you smell fuel or burning. With a fuel smell, switch the engine off, get everyone out and don't restart it. That is our inference from the fire risk: GM's manual warns that fuel vapors and fuel fires "burn violently".
If the light is steady and the engine runs smoothly, CARB says most manufacturers advise service "as soon as conveniently possible", and warns that extended driving without a fix could damage other components. Drive gently and get the codes read within days. Our guide Check engine light on: can I keep driving? covers the other warning lights that outrank this one.
What causes P0300?
A random misfire often has a cause that affects every cylinder, rather than one bad part. These causes come from manufacturer bulletins; each applies to the vehicles named.
| Cause | What the source says | Source |
|---|---|---|
| Wiring, grounds, poor fuel | Misfire faults "have commonly been related to" loose or damaged electrical connections, circuit grounds and poor fuel quality (2008–2023 VW gasoline engines) | VW 01-16-13 |
| Running very low on fuel | Cylinder misfire codes stored alongside a low-fuel-level code likely came from the low fuel, not a failed part | VW 01-16-13 |
| Spark plugs, ignition coils, injectors | For a single-cylinder misfire, VW has technicians swap these between cylinders to see whether the misfire follows the part | VW 01-16-13 |
| Injector installation or fuel contamination | On some 2016 Honda Pilots (a VIN range, built on or before March 1, 2016, with at least 5,000 miles), improperly installed injectors or contamination in the fuel system could set P0300; the fix was new injectors | Honda 18-025 |
| Ice in the exhaust | On some 2014–2018 Mazda3, 2014–2017 Mazda6, 2016–2017 CX-3 and 2013–2017 CX-5 models, water that froze in the main muffler after an overnight park below 0 °C (32 °F) could restrict the exhaust and cause a rough idle and P0300–P0304 | Mazda 01-006/18 |
| A lean mixture | Our inference, not from these bulletins: an engine running lean on all cylinders can misfire on several of them. If you also have P0171 or P0174, see P0171 and fuel trims | — |
VW's bulletin also says that multiple parts "SHOULD NOT be replaced" for one misfiring cylinder. It tells technicians to deal with any other stored codes before the misfire codes.
What should you do about P0300?
- Read every code, including pending ones. Look for cylinder-specific codes (P0301–P0308), lean codes (P0171, P0174) and fuel-level codes. Our explainer on pending, stored and permanent codes covers why pending codes matter.
- Note when it happens. Is it on a cold start, at low fuel, after a fill-up, or under load? VW has technicians use the freeze-frame data to tell sporadic misfires from cold-start ones. California's rule requires the car to record engine speed, load and warm-up status at the first misfire.
- Ask a dealer about bulletins and campaigns for your model. The Honda and Mazda cases above had specific fixes.
- Don't replace parts on a guess. Diagnose first, as VW tells its technicians to.
- Fix misfires before anything else. Repeated misfire can damage the converter and set P0420.
- Don't just clear the code. It comes back if the misfire is still there. Clearing also resets the readiness monitors, so the car reads "not ready" for an emissions test until it has been driven enough. See why a car says "not ready".
Where Tachwise fits
The Tachwise app beta reads stored, pending and permanent codes today, through your own Bluetooth ELM327 dongle in Chrome on Android or a computer. It shows whether P0300 came alone or with cylinder, lean or other codes, and it never clears codes. It does not read per-cylinder misfire counters. The Tachwise device, still a prototype, is being built to catch pending codes before the light comes on. Try the app beta or join the waitlist.
Frequently asked questions
Is P0300 serious?
It can be. A steady light with a smooth-running engine usually means service soon, not an emergency. A flashing light means misfire at a level the manufacturer has found can overheat and damage the catalytic converter, so reduce speed and load, follow your owner's manual, and stop driving soon.
Can bad fuel cause P0300?
Yes. Volkswagen lists poor fuel quality among common misfire causes, and GM's owner's manual says poor fuel can turn the check-engine light on and that it may take at least one full tank of the proper fuel to turn it off. Running very low on fuel can also cause misfires, according to Volkswagen.
Why did P0300 appear on a cold morning?
On some 2014–2018 Mazda3, 2014–2017 Mazda6, 2016–2017 CX-3 and 2013–2017 CX-5 models, Mazda says water that collected and froze in the main muffler after an overnight park below 0 °C (32 °F) could restrict the exhaust and cause a rough idle and misfire codes, including P0300. Other makes can have other cold-start causes, so check for bulletins on your model.
Will the check-engine light go off by itself?
It can. Under California's OBD-II rule, the light for a misfire may go out after three driving cycles in a row in which the engine runs at similar speed, load and temperature to when the fault was found, without misfiring again. The code stays in memory for a while afterwards.
Why is my light steady when the engine is shaking?
Some cars cut fuel to the misfiring cylinder instead of flashing the light, which California's rule allows, and a manufacturer can get approval to keep the light steady for extreme misfire. A steady light does not prove the misfire is mild, so treat a shaking engine as seriously as a flashing light.
Sources
- Cal. Code Regs. tit. 13, § 1968.2, Malfunction and Diagnostic System Requirements (OBD II). California Air Resources Board, via Cornell Legal Information Institute. Accessed .
- On-Board Diagnostic II (OBD II) Systems Fact Sheet. California Air Resources Board. Accessed .
- US5044194A: Misfire detection in an internal combustion engine (1991). Ford Motor Company, via Google Patents. Accessed .
- 2025 Chevrolet Equinox Owner's Manual. General Motors. Accessed .
- 2019 Honda Fit Owner's Guide: Dashboard Details. American Honda Motor Co.. Accessed .
- Technical Service Bulletin 01-16-13: Engine, Misfire Diagnostic Aid (2022). Volkswagen Group of America, via NHTSA. Accessed .
- Bulletin 01-006/18: Rough Idle and/or MIL On with DTC P0300–P0304 in Cold Temperature (2018). Mazda North American Operations, via NHTSA. Accessed .
- Service Bulletin 18-025: 2016 Pilot, MIL Comes On with DTC P0300–P0306 or P219A/B (2018). American Honda Motor Co., via NHTSA. Accessed .
Hear first when the Tachwise device is ready
Join the free waitlist: no payment, no deposit. Or try the app beta today; it reads your car's codes through your own ELM327 Bluetooth dongle.