P0300 — Random / multiple cylinder misfire detected
The computer saw misfires that aren’t pinned to one cylinder — spark, fuel, or air isn’t lighting off evenly across the engine.
What it means in plain English
P0300 means random or multiple-cylinder misfire. Unlike P0301–P0308 (specific cylinders), this points to something shared: fuel quality, vacuum leak, coil pack on older designs, MAF issues, low compression across cylinders, or several weak plugs/coils. A flashing check-engine light with misfire can dump raw fuel into the catalytic converter — treat it as urgent.
Common causes
- Worn spark plugs or multiple weak ignition coils
- Fuel quality / contaminated fuel; clogged filter
- Vacuum leak or intake gasket issues
- MAF or fuel-pressure problems
- Mechanical issues (timing, compression) in rarer cases
What you can safely check
- If the light is flashing: reduce load, avoid highway hills, get to a safe shop — continued driving can damage the cat.
- Note when it happens (cold start, acceleration, idle).
- Check for obvious vacuum hose cracks you can see without tools; don’t yank sensors.
- Scan for companion codes (cylinder-specific misfire, lean/rich, cam/crank).
Pull the code yourself (disclosed)
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A reusable Bluetooth OBD-II scanner lets you read the code and freeze-frame data before authorizing “mystery” diagnostics. One option: BlueDriver Bluetooth Pro OBD-II scan tool (BlueDriver/Levanta affiliate). Any capable OBD-II reader is fine — this is not required to use Fair Auto Shops.
When to go to a shop
Any flashing CEL, rough running, or repeated P0300 needs a shop with real diagnostics (power balance, fuel pressure, smoke test) — not a “tune-up kit” thrown at the code. Use how to read an estimate before authorizing.
Typical related repair costs (U.S. national averages)
These are related repairs shops may find after diagnosis — not a guaranteed bill for every P0300. Ranges exclude taxes, fees, diagnostics, and your location.
- $288–$399 national average for spark plug replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $184–$270; parts $104–$129.
- $238–$320 national average for ignition coil replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $74–$109; parts $164–$211.
A full plug set is often cheaper than guessing coils one at a time — but shops should test, not parts-cannon.
Related cost guides: Spark Plugs · Catalytic Converter · Ignition Coil
Questions to ask before you authorize work
Use questions before you authorize a repair and how to read a repair estimate. Watch for patterns in spotting upselling.
Find an honest independent shop
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FAQ
Is a flashing check-engine light with P0300 an emergency?
Treat it as urgent. Ongoing misfire can overheat and destroy the catalytic converter. Ease off and get diagnosis soon.
More check-engine codes
P0420 · P0430 · P0301 · P0171 · P0174 · P0455 · P0456 · P0442 · P0446 · P0128 · P0401 · P0133 · P0113 · P0506 · P0507 · P0700 · P0741 · P0011 · P0325 · P0340 · P0335 · P0101 · P0299 · P0135 · P0440 · P0441 · P0010 · P0500 · P0121
Hub: How to read a check-engine code · Repair cost guides · Affiliate disclosure