Signs of Bad Ignition Coils and Average Replacement Costs

What are the functions of an ignition coil, and how does it work? Under this guide, we provide information about ignition coils. It offers valuable information to help drivers identify bad coil pack symptoms and average replacement costs and answers some commonly asked questions about ignition coils.

How the ignition coil works

The ignition coil is a powerful electric device that converts battery voltage (12V) to a higher magnitude. The high voltage is required for igniting the fuel for ultimate engine performance. There is a single ignition coil for every spark plug. For ignition to occur, the coil needs supplies 15000-20000 volts. The high voltage generates a spark that ignites the fuel.

A bad coil pack causes poor fuel consumption and can result in engine misfires. Ignition coil problems could also arise from the battery used. The voltage supply could be too low or higher than the coil’s designed capacity.

Signs of a bad coil pack

Low fuel economy

High or abnormal fuel consumption is one of the early signs of a bad ignition pack. The ignition coil cannot ignite the fuel as required, and the car depicts lower mileages than before. Checking the ignition coil could provide answers regarding the erratic consumption.


It is a common indicator of a damaged ignition pack. Backfiring occurs when the unburnt fuel leaves the engine through the exhaust pipe. The phenomenon is associated with dire consequences that culminate in costly engine damages. The emission of black smoke and smelly exhaust gases are common signs of a backfiring engine.

Misfiring engine

When driving with a bad ignition pack, the driver notices that the engine has a sputtering noise. A misfiring engine causes the car to jerk with a spitting sound. Other signs of a misfired engine are violent vibrations when idling.

Low power, jerking and rough idling

A bad coil pack causes a myriad of challenges. Poor fuel ignition translates to lower engine power. We have mentioned that it causes the engine to misfire. The result is jerking, rough idling and poor responsiveness to acceleration.

Engine stalling

When the ignition coil damage persists, the engine begins stalling. The ignition coil delivers irregular sparks. It means that the engine will experience instances of no power. It causes the car to stall.

Check engine light comes on

The P0351 error code appears on the dashboard. The light is an indication of a bad coil pack.

Hard engine start

Since the vehicle depends on the spark plugs for ignition, drivers will likely experience difficulty starting the car. The engine will crank. But because the ignition coil is faulty, there is no spark for ignition.

The average cost for replacing a bad coil pack

The cost of a new ignition coil can be as low as $75 and as high as $300. The price could be higher than this for other car brands. The labor costs are between $100 and $200. The repair shop will charge you a minimum of $150 to replace a bad ignition coil.


When the ignition coil is bad, the driving experiences are equally chaotic. It causes issues ranging from backfiring and misfiring to poor fuel economy. When the aforementioned signs begin manifesting, it is crucial to have the ignition coil replaced.


What are the indicators of a bad ignition coil?

The engine misfires. There is backfiring, poor fuel consumption and cases of hard engine start.

Is it okay to drive with a faulty ignition coil?

You can drive with a faulty ignition. However, it is not advisable as the risks involved are plenty and costly.