P0304: cylinder 4 is misfiring
A misfire is a cylinder not burning its fuel properly, which the engine control unit detects from small, repeated changes in how smoothly the crankshaft is turning. This code means the computer has traced the misfiring specifically to cylinder 4, unlike a random misfire code that can't be pinned to one cylinder.
You might notice
- The engine feels rough, shakes, or hesitates, worse at idle than at speed
- The engine warning light comes on, and may flash if the misfire is severe
- misfire
- — a cylinder not burning its fuel properly
What the code itself says
P0304 is a powertrain (engine, gearbox and drive system) code, and the 0 after the letter means it is a generic code with a standard meaning.
Grouped here as: Engine running, fuelling and misfires — Air metering, fuelling, ignition, misfire, idle, boost, knock, oxygen sensors and the catalyst, all working together in the running engine. That grouping is ours, to help explain the code. The code's official family is the letter at the start.
This page is generic. Your car isn't.
A code on its own only tells you what the sensor saw, not what's actually wrong — and that changes next to your other codes. Read this one together with the rest of your scan and we'll work out what's really going on.
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