Your car needs a spark to run—and that spark comes from the ignition coil. It’s a small but mighty part of your vehicle’s engine system.
If it goes bad, your engine won’t perform the way it should. You might feel a rough idle, hear weird noises, or even find yourself stranded with a car that won’t start.
Let’s dive into what the ignition coil does, what symptoms to watch for, what causes it to fail, and how to handle the problem before it gets worse.
This guide is designed for an 8th-grade reading level, so it’s easy to understand even if you’re not a mechanic.
What Does the Ignition Coil Do?
Think of the ignition coil like a mini transformer. Its main job is to take the low voltage from your car’s battery and turn it into a high-voltage charge. This high-voltage energy is then sent to the spark plugs.
The spark plugs use it to create a spark that lights the air and fuel mixture in each cylinder. That explosion powers your engine.
Without a strong spark, your engine can’t fire properly. If the ignition coil is weak or broken, your car may not start, may misfire, or may run rough. So while this part might seem small, it’s extremely important to your engine’s health.
Why It’s Important to Recognize the Signs
A bad ignition coil doesn’t just mess with your engine—it can lead to damage in other areas too. For example:
- It can cause your spark plugs to wear out faster.
- It can damage your catalytic converter, a very expensive part.
- It can leave you stuck with a dead engine on the side of the road.
Recognizing the symptoms early can save you time, money, and stress. Many of these signs are easy to spot once you know what to look for.
Common Symptoms of a Bad Ignition Coil
Here’s a closer look at the most common signs that your ignition coil might be failing.
1. Engine Misfires or Hesitates
If your engine feels like it’s skipping or stumbling, especially when you press the gas pedal, that’s often a misfire. This happens when one or more cylinders don’t get a proper spark. Instead of a smooth ride, you’ll feel jerks or shaking, especially while accelerating or going uphill.
You might also hear popping sounds or feel the car vibrating while it’s idling. These signs should never be ignored. The longer you wait, the more damage could be done to your engine and exhaust system.
2. Poor Fuel Economy
A bad ignition coil can hurt your gas mileage. When the spark isn’t strong enough, the fuel in the engine doesn’t burn completely. That means wasted fuel—and more money spent at the pump.
If you notice that you’re filling up the tank more often than usual, and you’re driving the same routes as before, this could be a clear sign that something in the ignition system isn’t working right.
3. Hard Starts or No Start
A failing ignition coil can make your car hard to start—or prevent it from starting altogether. You might turn the key, hear the engine crank, but it doesn’t catch and start. That’s because the spark needed to fire up the engine is missing.
In cold weather, this issue is even more noticeable. Your engine needs a strong spark to overcome the cold. If the ignition coil is weak, it might take several tries to get the engine going, or it may not start at all.
4. Check Engine Light Is On
When your ignition coil goes bad, your car’s computer (ECU) often notices right away. It will turn on the check engine light to warn you that something’s wrong.
If you have an OBD2 scanner, you can plug it in to read the trouble codes. Common codes linked to ignition coil problems include:
- P0300–P0312 (random or specific misfire)
- P0350–P0362 (ignition coil circuit faults)
Even if the light turns off later, don’t ignore it. It could mean the problem is intermittent—or getting worse.
5. Backfiring or Loud Exhaust Noise
When fuel doesn’t burn inside the engine, it can travel to the exhaust system. Once it hits a hot part of the exhaust, it might ignite suddenly, causing a loud pop or bang from the tailpipe. This is called backfiring.
Backfiring isn’t just loud—it can damage your exhaust system and hurt your car’s performance. You might also smell gas or hear crackling sounds from the rear of your vehicle. These signs are all red flags that the ignition coil might be misfiring.
6. Loss of Power While Driving
A failing ignition coil can make your car feel sluggish. You might press the gas and not get the response you expect. It can feel like your car is dragging or refusing to pick up speed.
This lack of power is especially noticeable when climbing hills, merging onto highways, or trying to pass another vehicle. Sometimes, the engine may even stall or shut off briefly while driving.
If your car suddenly loses power or feels weak, it could be a bad ignition coil causing it.
7. Strong Fuel Smell
If the spark from the ignition coil isn’t strong enough to ignite all the fuel, that extra fuel exits the engine unburned. It travels through the exhaust system and gives off a strong gasoline smell.
This smell might come from the tailpipe or even from under the hood. It’s a sign that fuel is being wasted, and it can also mean the emissions system is being stressed or damaged.
What Causes an Ignition Coil to Go Bad?
Several things can cause ignition coil failure, including:
- Old Age: Like many parts, coils wear out over time. Most last 100,000 miles or more, but some fail earlier.
- Heat and Vibration: Excessive engine heat and constant vibration can crack the coil’s casing or loosen internal connections.
- Worn Spark Plugs or Wires: Bad spark plugs make the ignition coil work harder. Over time, this can cause overheating and failure.
- Moisture or Oil: If water or engine oil leaks into the ignition system, it can cause the coil to short out or corrode.
Can You Still Drive With a Bad Ignition Coil?
Technically, yes—you can drive with a bad coil, but it’s not smart. Here’s why:
- You risk further engine damage.
- You’ll waste fuel.
- Your emissions will go up.
- Your car might stop running suddenly.
Even short drives can add stress to other parts like spark plugs, sensors, and the catalytic converter. It’s better to fix the issue right away.
How to Fix a Bad Ignition Coil
If you’re handy with basic tools, you may be able to replace the ignition coil yourself. Here’s a simple step-by-step guide:
- Turn off the engine and disconnect the battery.
- Locate the ignition coil(s). In some cars, there’s one per spark plug; in others, one coil serves several plugs.
- Unplug the electrical connector from the coil.
- Remove the mounting bolts.
- Pull out the old coil.
- Install the new coil, bolt it in place, and reconnect the plug.
- Reconnect the battery and start the engine.
If this sounds too technical or your car is hard to work on, a mechanic can usually handle the job quickly and affordably.
Final Thoughts
When it comes to engine issues, spotting the signs early makes all the difference. A bad ignition coil can cause misfires, poor gas mileage, starting trouble, loud noises, and even total engine failure.
But the good news? Most of these symptoms are easy to spot, and replacing a coil is usually a quick fix.
So the next time your car starts acting up, don’t wait. Pay attention to the signs, check the ignition coil, and take action. You’ll avoid bigger repairs—and keep your engine running like it should.
