One of the latter is your Volvo's ignition coil. Also called a spark coil, the ignition coil is an induction coil in the automobile's ignition system. The Volvo ignition coil transforms a storage battery's 12 volts into the thousands (which sometimes could reach as high as 120,000 volts) needed to ignite the spark plugs.

Invented by A. Kent Atwater in 1921, the ignition coil is a simple transformer that has two sides: the 12 volt or primary side and the high voltage or secondary side. The primary side contains a few hundred turns of a large diameter wire and it builds up the magnetic field in the coils. On the other hand, the high voltage side contains thousands of turns of small diameter wire. The coil uses ?electromagnetic induction? to create the high voltage. When the voltage in the primary side is turned off, the collapsing magnetic field in the secondary side induces a voltage in the secondary side, producing thousands of volts.

In older vehicles, a single, large ignition coil would serve all the spark plugs, distributing voltage via an ignition distributor. In modern systems, the distributor is omitted and ignition is controlled electronically, instead. Much smaller coils are used with one coil for each spark plug or one coil serving two spark plugs (so two coils in a four-cylinder car). These coils may be remote-mounted or they may be placed on top of the spark plug (coil-on-plug or direct injection). Where one coil serves two spark plugs (in two cylinders), it is through the "wasted spark" system.

In this arrangement, the coil generates two sparks per cycle to both the cylinders. The fuel in the cylinder that is nearing the end of its compression stroke is ignited, whereas, the spark in its companion nearing the end of its exhaust stroke has no effect. The wasted spark system is more reliable than a single coil system with a distributor and cheaper than coil-on-plug.

Where the coils are remote mounted, they may all be contained in a single molded block with multiple high-tension terminals. This is commonly called a coil-pack.

Your Volvo ignition coils are part of a larger system, which is the ignition system. The ignition system is part of an even larger engine system. The ignition system's primary responsibility is the timely burning of the fuel-air mixture in the engine. Your Volvo user's manual would carry the recommended service interval for your ignition system, including your Volvo ignition coil.

Your Volvo engine might run rough, buck, surge, stall or even get poor fuel economy. These are signs that your ignition system might need servicing as they are potentially an ignition system problem.

When this happens, drive to the nearest Volvo dealership and have a qualified technician take a look around. Your Volvo engine might be in problem in the long run.