Ignition coil, cylinder 4 — circuit malfunction
Where to start
The coil circuit of cylinder four. Swapping the coil separates coil from wiring in five minutes. On an inline four this is the end cylinder by the bulkhead: water from under the windscreen runs down there, and a flooded connector is a common cause of this particular code rather than its neighbours. The partner code is P0304.
What the cylinder number gives you
The last digit names the cylinder: 4. 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 4 and a neighbour, clear the code and drive. If the fault follows the part, the part is to blame. If it stays on cylinder 4, 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.