Signs of a failing ignition coil

There are many different signs of a failing ignition coil. For a completely dead ignition coil, The most common is a misfire feeling. If the coil is completely dead, this is accompanied by a check engine light, and a  "chugging along" feel when you drive your car. Other symptoms are a check engine light and/or a slight hiccup, surge, hesitation or skipping feeling while driving. When using an OBDII scanner, common misfire codes are the following:

• P0300 -Random misfire - this is when your computer is not able to pinpoint the exact cylinder. Sometimes it can only be one cylinder misfiring, or it can actually be random.
• P0301 - Cyl 1            
• P0302 - Cyl 2
• P0303 - Cyl 3
• P0304 - Cyl 4
• P0305 - Cyl 5
• P0306 - Cyl 6
• P0307 - Cyl 7
• P0308 - Cyl 8
• P0309 - Cyl 9 
• P0310 - Cyl 10
• P0311 - Cyl 11
• P0312 - Cyl 12

If the coil is not completely dead, there are many symptoms that you may experience. You may feel slight hesitation when you step on the gas. Weak ignition coils will misfire under a load. (aka acceleration, or uphill driving) and may operate perfectly fine when cruising. Sometimes a check engine light may be on, and other times there may be no check engine light. Some (but not all) vehicle computers will not turn the check engine light on for an occasional misfire, but rather record the misfire and store it in the computer to monitor it for a period of time, then determine if the problem is significant enough to alert the driver. To find these misfires that are stored, you can use a OBDII scanner with "mode 6" capability.  These usually start at around $100. While it may seem like a lot of money, consider how much your local garage may charge you just for a one time diagnostic. This tool can help tremendously, and can be used on every vehicle you own. Unless you have an oscilloscope, the best way to test ignition coils is while they are still in the vehicle. The multi-meter test will not be as accurate for coils that malfunction occasionally are not completely blown. This is why we reccomend using an OBDII scanner with mode 6 capability.