7 Popular Bad Ignition Coil Symptoms


How do you know the car’s ignition coil is in trouble? When it shows erratic behavior and does not run smoothly. The coil supplies power to the spark plugs from the generator. It ignites the fuel and provides the engine enough power to run the vehicle. When it fails, your car will show difficulties to start. So, you have to know what the bad ignition coil symptoms are to identify the problem and take necessary action

7 Bad Ignition Coil Symptoms

There is a dedicated ignition coil for each of the spark plugs. They are connected either directly or via wires. The plugs require around 15,000 to 20,000 volts of electricity to create the spark to ignite the fuel. So, even the slight glitch can result in big issues. Learn the bad ignition coil symptoms to keep your car healthy and trouble-free:


It’s one of the earliest symptoms and taking actions during this period will help you to avoid costly repairs down the road. Watch out for the emission of black smoke and the stench of gasoline at the time of starting the engine. Ignoring it can eventually damage the exhaust system.

bad ignition coil symptoms
Backfiring shows at the earliest period. (photo source: Mercedes-Benz)

Misfiring of the Engine

It happens when the coils have failed. The engine will make coughing noises and cause a bumpy ride at high speeds by jerking and spitting. Your car won’t get enough power at the time of driving. The failed coils will also be the reasons for vibrating when idling.

Issue at Engine Starting

It is obvious because ignition coils help the engine to kick off. So, any problem with them will affect this function. You can be certain that the problem is with the coils when the car shows trouble starting in cold weather.

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Engine Hard Starting

Some models use a single coil for creating the ignition spark. So, all the cylinders will be affected when there’s a malfunction with the coil. The engine will crank but there will be no spark and the car won’t start.

Engine Light Code On

Bad ignition coil symptoms also include the turning on of the engine light code located in the combination meter. The common code is P0351, which indicates a primary or secondary-level circuit malfunction in the ignition coil. When it happens, you have to check the glitch by using a diagnostic tool.

It will be a DTC light turning on if you are driving a BMW model.

bad ignition coil symptoms
Use a scanner when the light code is on.

Vehicle Stalling

This annoying is another consequence of driving with a failed ignition coil. It results in creating irregular sparks to the plugs, causing the vehicle not to get enough power. Thus, the car may stall frequently and totally shut off at some point. In that case, you have to restart it.

Poor Fuel Economy

A bad ignition coil can’t supply the required power to the spark plugs. As a result, the car struggles to start the engine and uses more fuel to make up for the lost power. The consequence? Losing mileage for each gallon.

The video shows you how to identify a bad ignition coil with just a simple test light