CodelampCame back after a repair
P0300 came back after new ignition coils
P0300
- In plain words
- More than one cylinder, or no single one, is misfiring.
- Standard name
- Random/Multiple Cylinder Misfire Detected
- System
- Ignition and misfire
General information, not a mechanic's diagnosis: have a mechanic confirm before any repair.
What the computer saw
New coils fix misfires when the coils were the cause. If P0300 is back, the misfires come from something the coils do not touch: the plugs, the fuel, the air or the engine itself.
Likely causes, most common first
- Worn spark plugs. Coils replaced without new plugs can still misfire.
- A vacuum leak or lean mixture. A lean code beside it points here.
- Fuel injectors or fuel pressure. A clogged injector misfires its cylinder.
- Wiring or a connector for the coils. A damaged connector stops a new coil from firing.
- A mechanical problem. Low compression or valve trouble.
What you can note yourself
- Note whether the plugs were changed with the coils.
- Note whether the light is steady or flashing, and tell the shop.
What to tell the shop
- When the coils were replaced, and whether plugs were too.
- Any cylinder or lean codes now stored.
This page gives no verdict on whether a car is safe to drive; a mechanic can.