Ignition coil, cylinder 3 — circuit malfunction
Where to start
The coil circuit of cylinder three. Swapping the coil to a neighbouring cylinder answers the main question for free: if the code moves, it is the coil; if it stays, it is the wiring. On an inline four, cylinder three sits closer to the flywheel and its connector is usually the last one people reach — which is also where a wire chafed against a bracket is most often found. The partner code is P0303: a misfire in the same cylinder.
What the cylinder number gives you
The last digit names the cylinder: 3. That is the most useful thing in this code — it turns a search across the whole engine into a check of one cylinder.
Swap and watch. Move the coil between cylinder 3 and a neighbour, clear the code and drive. If the fault follows the part, the part is to blame. If it stays on cylinder 3, the cylinder is: the injector, compression, a valve. This is the only way to tell one from the other without taking anything apart.
⚠️ This code is about the CIRCUIT, not the spark: the connector and the wire come before the coil itself. A coil is often replaced when the trouble was a corroded contact.
How to put together a report a mechanic will actually read
How the code is built
All codes in «Ignition system and misfires»
How the app helps
CarScan reads this code from your car through an OBD-II adapter, shows whether it is active now or only stored, names the module that reported it, and puts it into a plain-text report for your mechanic.