Change an Ignition Coil

Steps

1. Know the signs. A failing coil makes the engine shake at idle, lose power, misfire under load or light the engine warning lamp. A workshop or a code reader can tell you which cylinder misfires.
2. Get the right coil. Coils differ by engine, so choose one for your car's engine and model years ("Parts for your car" below). Old spark plugs often damage coils: if your plugs are due, change them at the same time.
3. Find the faulty coil. Switch off and open the bonnet; take off any engine cover. On many engines there is one coil on top of each spark plug. If you know the misfiring cylinder, your handbook or a workshop can show which coil that is.
4. Check by swapping, if you are not sure. Swap the suspect coil with the one next to it, clear the fault, drive, and see whether the misfire moves with the coil. If it moves, the coil is faulty.
5. Unplug the coil. Press or slide the clip on its connector and pull the plug off. Do not pull on the wires.
6. Take out the coil. Undo its bolt, then pull the coil straight up with a gentle twist. Look into the plug well: it should be dry and clean.
7. Fit the new coil. Push it down straight over the spark plug until it seats, then refit its bolt and tighten it gently; it holds only the coil.
8. Plug it in until the connector clicks. Refit the engine cover.
9. Start and test. The engine should idle smoothly. If the engine light was on, have the fault cleared with a code reader, then drive and check that it stays off.