The first step in testing ignition coils is to take them out of the engine. In all models, except 2006 and earlier 2.7L V6 models, an ohmmeter should be connected to measure insulation resistance between terminal number one in the connector and the spark plug terminal.The reading will be very high or infinity if it is good. After that measure primary winding by connecting an ohmmeter between both high voltage terminals for comparison of readings. This can also be cleared up by swapping a coil with another cylinder, then checking for misfire codes as confirmation that the problem is within that area. For 2001 through 2006 2.7L V6 models, disconnect spark plug wires from each spark plug and the primary wiring connector should be disconnected before measuring secondary resistance between spark plug terminals. Primary resistance may also be measured between some other corresponding terminals to check on the condition of coils themselves.For newer models since 2007 connect an ohmmeter across two primary windings and compare readings with respective specifications.Avoid replacing coils having greatly differing values; small variations are considered normal.Secondary resistances are not available.Replace negative battery cable in order to remove cover over engine, following specific instructions for removing one depending on model/year of vehicle when you need to change those parts.