Ignition Coil Failure: Symptoms, Codes and Fixes

Ignition coils are a common cause of misfires on modern cars, and we see them fail regularly on popular Japanese imports. Knowing the symptoms helps you catch the problem before it causes more damage.

What an ignition coil does

The ignition coil turns your battery's 12 volts into the very high voltage needed to create a spark at the spark plug. Most modern engines use one coil per cylinder, mounted directly on top of the spark plug.

Symptoms of a failing coil

• Engine shaking or running rough, especially at idle

• Hesitation or jerking when accelerating

• Loss of power

• Worse fuel economy

• A flashing or steady check engine light

• The engine stalling or being hard to start

Common fault codes

• P0300: random or multiple misfires

• P0301 to P0304 (or higher): misfire in a specific cylinder

• P0351, P0352, P0353 and so on: a problem in the primary or secondary circuit of ignition coil A, B, C and so on

When several coil circuit codes appear together, the fault may be shared wiring, a connector, a ground or power supply problem rather than every coil failing at once. That's why testing matters before buying parts.

Why coils fail

• Heat and vibration over time

• Worn spark plugs, which force the coil to work harder

• Oil leaking from the valve cover into the spark plug wells

• Moisture getting into connectors

• Damaged wiring or connectors, sometimes from previous repairs

How a mechanic confirms it

A common test is swapping the suspect coil to another cylinder and seeing if the misfire moves with it. We also check the wiring, connectors, power supply and ground, and inspect the spark plugs.

The repair

Replacing a coil is usually straightforward on most four-cylinder engines. It's often wise to replace the spark plugs at the same time if they're due, and to fix any oil leaks into the plug wells so the new coil doesn't fail early.

Don't drive on a misfire for long

A misfiring cylinder sends unburned fuel into the exhaust, which can overheat and damage the catalytic converter, a much more expensive part to replace.

Need help with this? RCJ Mobile Mechanics comes to you in Portmore, Spanish Town, Kingston, St. Andrew and across St. Catherine. Call or WhatsApp (658) 207-6565 or book a mechanic online.