What does it mean?
The ignition system converts battery voltage into the high voltage used to ignite the cylinder air/fuel mixture. The low voltage side of the system is referred to as the primary circuit. It includes the battery, ignition switch, primary coil winding, a triggering mechanism (such as a crankshaft sensor) and switching device (such as an ignition module or ECU). The high voltage side of the system is called the secondary circuit. On modern vehicles it includes the coil pack and spark plugs.
Current technology has done away with many ignition components of the past. This includes items such as the distributor, cap, rotor – and now even the spark plug wires. Modern engines use only a coil pack that sits directly on top of the spark plug. A coil pack The coil pack is used to convert the low primary circuit voltage to high secondary voltage needed to fire the plugs. The coil pack is basically a transformer, which has coils of wire inside.
The primary side has a few hundred turns of wire, whereas the secondary side has thousands. Current is applied to the primary side of the coil, which creates a magnetic field around the winding. Then, the current is interrupted by a switching device (usually the PCM). This causes the magnetic field to collapse, inducing a voltage into the winding. Simultaneously, the collapsing magnetic field creates a voltage in the secondary winding.
Since the secondary winding contains many more turns of wire, output voltage is increased to thousands of volts. This is enough to fire the spark plugs. The PCM sets an ignition coil control circuit code P0350 to P0362 when it detects a problem with the ignition coil circuit. The last digit of these codes references the cylinder where the issue is occurring. For example, P0351 indicates a fault in the #1 cylinder coil circuit.
Likewise, P0359 indicates a problem with the coil circuit on cylinder #9 on a V10 or V12 engine.