Ignition Coils & Modules

Move it. Read the code to find which cylinder is misfiring, then swap that coil with one from a healthy cylinder and clear the fault memory. If the misfire moves to the cylinder you moved the coil to, the coil is confirmed and you have spent nothing to prove it. If the misfire stays where it was, look at the spark plug, the injector and the compression on that cylinder instead. This test takes ten minutes and prevents most unnecessary purchases.

Consider how the fault arrived. Coil failure tends to be sudden, affecting one cylinder, and often worse under load or when hot. Plug wear is gradual, affects all cylinders together and shows as a slow loss of smoothness and economy. If the plugs are near their replacement interval, change them first since they are cheaper and a worn plug with a wide gap makes the coil work harder and shortens its life. Then retest before ordering a coil.

It depends on mileage and how the failure arrived. On a low mileage engine where one coil has failed early, replace that one. On a high mileage engine, the remaining coils have run the same hours in the same heat and are statistically close behind, so replacing the set avoids repeating a job you have already learnt to do. There is no requirement to match coils as a set, unlike some components, so either approach is technically sound.

A flashing lamp means a misfire severe enough to risk damaging the catalytic converter with unburnt fuel, which is a different warning from a steady lamp. Reduce load, avoid high engine speeds and get the fault read promptly. Continuing to drive hard with a flashing lamp is how a coil failure turns into a converter replacement. If the misfire is confined to one cylinder and the plugs are recent, a coil is the most likely single cause.

Both, and they are worth checking before fitting a new one. Oil in the spark plug well, usually from a leaking cam cover seal or plug tube seal, soaks the coil boot and lets the spark track to earth rather than reaching the plug. Water sitting in the well after washing does the same. If a plug well is wet or oily, cure the leak, clean the well and dry it thoroughly, or the replacement coil will fail in the same way.

A coil is one of the cheaper engine electrical parts, which matters because replacing a full set on a high mileage engine is a realistic decision rather than an extravagance. Separate ignition modules on the older applications cost more. The live spread for this category sits in the band overhead. Compare that against the alternative. A misfire left running feeds unburnt fuel into the catalytic converter, and a converter is one of the more expensive parts on the car, so a set of coils is cheap insurance once one has failed.

On almost every coil on plug engine, yes, and it is one of the easiest repairs available. Switch off, disconnect the connector, remove the single retaining bolt, and pull the coil straight up out of the plug well with a gentle twist. Fit the new one with a smear of dielectric grease inside the boot, seat it fully so it clicks onto the plug, and refit the bolt. Budget ten minutes per cylinder, and clear the fault memory afterwards.

Look for what is stressing it. An excessively wide spark plug gap forces the coil to generate more voltage than it was designed for, and the extra heat and stress shorten its life dramatically. Oil in the plug well, a cracked boot allowing tracking, and a lean or misfiring cylinder for another reason all do similar damage. A coil is the visible casualty rather than the cause, so investigate the plug condition and the well before fitting a second replacement.

None directly, and the plugs beneath them are the maintenance item that determines their life. Replacing spark plugs at the specified interval keeps gaps in range so coils are not asked for excessive voltage, and inspecting the plug wells at the same time catches oil leaks before they soak the boots. Applying dielectric grease inside the boot on refitting helps the boot seal and makes future removal easier without damaging it.

Only where the number agrees. Primary resistance, secondary output, connector pinout and boot length all follow the specific engine, and a coil with a shorter boot will not seat on the plug while one with the wrong resistance stresses the driver circuit in the control unit. Since coils look broadly alike, this is a category where the number matters more than the photograph. Read your existing part number and match it, or use the quote form.

On older systems, a separate module contained the switching transistors that made and broke the coil primary current. On current engines that function is built into the control unit or into the coil itself, so there is no separate module to replace. If your vehicle is recent and coil on plug, assume the driver is integrated. Where a coil driver circuit inside the control unit fails, the symptom is a dead cylinder that does not respond to a coil swap.

Yes. Coils are usually priced because they sell steadily, so a blank field here normally belongs to an older application or to a separate ignition module. Send the number and the answer comes back on it. Order a full set rather than one coil if the engine has covered serious mileage. Coils age together, the remaining ones are the same age as the failed one, and a second misfire two months later means the plugs come out again. Include the plug well boots and seals, since a coil dropped into an oil filled well fails early every time.