FAILING IGNITION COILS
If the engine is running roughly or misfiring, possibly to the extent that it is
effectively undriveable, and the engine warning lamp is illuminated on the dash, with a cylinder-specific fault code stored, this points to ignition coil failure.
If possible, carry out a full fault code check of the engine control unit (ECU) – you will almost certainly find a stored fault code relating to a misfire specific to a particular cylinder. So if the fault is in cylinder No 1 the code would be ‘P0301’; ‘P0302’ would indicate cylinder 2, and so on. Also, if available via the diagnostic tester in ‘actuators’, you can switch the fuel injector off/on to see if the misfire disappears on that cylinder. It’s worth
noting that any basic fault code reader can read engine faults if the warning light is illuminated, but a more sophisticated tool is needed for advanced programming and other ECU checks.
We have come across a Qashqai fitted with allegedly genuine NGK spark plugs bought via the internet, which turned out to be fake units that ended up burning out two coils.
A quick test that can help diagnosis is to swap the coils between cylinders, to see if the fault moves with the dodgy coil. An additional check is to look for signs of burning or a smell of burnt plastic.
You should always renew ignition coils in complete sets. If one coil has failed, it’s highly likely that the remaining ones won’t be far behind.