7 Symptoms of a Bad Ignition Coil and Replacement Cost

Last Updated on May 13, 2020

In this article, we are going to talk about the ignition coil, so you will know its basic functions, symptoms of a bad ignition coil, how to test, and also the average replacement cost.

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How an Ignition Coil Works

Ignition coils are known as compact electrical transformers. Their purpose is to take the low 12-volt current normally found in car batteries and convert it into a much higher voltage which is needed to ignite the fuel and start the engine.

Each spark plug in a car has its own ignition coil. The coil is either physically connected to the spark plug with wires or it sits on top of the spark plug without using wires.

The spark plug needs about 15,000 to 20,000 volts of electricity in order to form an electric spark that can ignite the fuel. If you don’t have strong ignition coils then it will result in weak fuel consumption or engine misfires.

ignition coil symptoms

It’s important to note that a troublesome ignition coil can also be related to a low voltage or abnormally high voltage battery. This will also cause a range of other issues with the car and upgrading it to a new battery can see many issues go away.

Many batteries found in older cars can simply breakdown with age and one sign of a bad battery is if it’s not reading at least 12.65 Volts when fully charged, you know there are issues with the battery.

Symptoms of a Bad Ignition Coil

If a vehicle is behaving intermittently and is giving its driver some trouble in a smooth driving, then it could indicate that the ignition coil of that vehicle has gone bad.

The failed or weak ignition coil symptoms may vary depending on the severity of the ignition coil failure. Here are some of the most common signs of bad ignition coil.

#1 – Backfiring

Backfiring caused by your vehicle can indicate the symptoms of the ignition coil failure in its early stages. Car backfiring occurs when the unused fuel in the combustion cylinders of the engine leaves through the exhaust pipe.

If this problem is left unchecked, then it can result in costly repairs. The backfiring problem can usually be detected by the emission of a black smoke through the exhaust pipe. The smell of gasoline in that smoke may also give away the ignition coil failure.

#2 – Poor Fuel Economy

bad fuel economy

Another sign of a faulty ignition coil is poor fuel economy. If your vehicle is getting noticeably less mileage than it was before, then it could mean that an ignition coil failure has occurred.

#3 – Engine Misfiring

cylinder misfire causes

Engine misfiring will be seen in a vehicle whose ignition coils have failed. Trying to start the engine of such a vehicle will result in engine misfiring that sounds like a coughing, sputtering noise.

When driving at high speeds, jerking and spitting will be seen in the behavior of the vehicle. A vehicle with a failed ignition coil will also result in vibration when it is idling at a stop sign or light.

#4 – Vehicle Stalling

tire noise

Ignition coil failure may also result in the stalling of that vehicle. This can occur because of the irregular sparks sent to the spark plugs by the faulty coil. Your car may shut off completely when brought to a stop leaving you with the trouble of it hopefully restarting.

#5 – Engine Jerking, Rough idling, Poor Power

rough engine idle

Another symptom is rough idling of the engine, jerking, and hesitating while accelerating. It will feel like your vehicle is missing some power when driving.

#6 – Check Engine Light On / DTC Code

Often, the check engine light will turn on in your dash. Most commonly, engine code P0351 (Ignition Coil – Primary/Secondary Circuit Malfunction) is what shows up when scanned using a car diagnostic tool.

Scanning for the error code is probably the easiest way to troubleshoot a coil issue, so if you see that check engine light, grab your scan tool or have a repair shop confirm.

#7 – Engine Hard Starting

A hard to start engine is a symptom that will occur especially if your car uses a single coil. If the coil has a malfunction, it means the engine will be cranking without sparks inside the cylinders.

Average Ignition Coil Replacement Cost

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cost to replace ignition coil

The cost of a new ignition coil depends on the make and model of the car. Some coils are as cheap as $75 while others cost in the $300 range. If you have the replacement professionally done then the labor costs will be between $50 and $100 per hour.

Therefore, you can expect to pay at least $150 to $200 if you were to take your car to an automotive repair shop and have them replace your ignition coil for you. If you choose to go to a dealership, expect to pay even more.

Read also: Average Fuel Filter Replacement Costs

How to Test an Ignition Coil

Here are some tips on testing an ignition coil based on whether they are a CNP (Coil-Near-Plug) or COP (Coil-On-Plug).

CNP Coil Type

  • To run a test on an ignition coil, first turn off your car’s engine and open up the hood. Remove or pull the spark plug wire from it (if you car uses CNP coils). These wires typically start from the distributor cap and run to the spark plug. Use rubber gloves and insulated tools when working with these electrical components or you may get a nice jolt.
  • Now attach the new spark plug to the spark plug wire (new or old spark plug to test coil sparks). Use insulated pliers to hold the spark plug onto some metal part of the engine so that the threaded portion of the spark plug is touching the metal.
  • Use a fuse removal tool or needle nose pliers to remove the fuse to the fuel pump to disable it and get ready to crank the engine. You may need an extra person to turn the key in the ignition because you are holding the spark plug down with the pliers.
  • Once the engine is cranked, look for blue sparks forming along the spark plug gap. If you see blue sparks then your ignition coil is working properly.
  • If you don’t see the sparks or if you see orange sparks then this is a sign of the ignition coil malfunctioning.
  • When you’re done with the test, disconnect the spark plug, place it back in its hole, reconnect the spark plug wires to it, and put back the fuel pump fuse.

COP Coil Type

  • Start the engine.
  • Keeps the engine running at idle speed.
  • Open the number 1 ignition coil bolt, and then pull up the coil to see how the engine runs.

If the engine’s condition changes to rough idling, that means the number 1 ignition coil is good. Then you can continue this step with the remaining coils one at a time until you find the culprit. When you pull out a faulty ignition coil, the engine condition/idle should not change.

 

73 thoughts on “7 Symptoms of a Bad Ignition Coil and Replacement Cost”

  1. My car ran out of oil its a Nissan fuga 2007 its rolling over but its not starting when the mechanic checked it with the device it said it needed cam sensors crank sensor and coils we changed the cam and the crank do you think its the coil? Or what to you think we need to look at?

    Reply
    • There are many possible causes for an engine losing power when hot.

      If you mean “when the ambient temperature is hot”, engines typically run a little slower when it’s hot outside, since hot air is less dense than cold air. Furthermore, hotter temperatures will tax the cooling system more and may cause the engine to pull timing, which reduces power. Timing is pulled to reduce the chance of preignition, which could damage the engine.

      If your car is overheating, you may be losing power due to the engine running above the operating temperature it was designed for. This could quickly harm the engine and cause further damage if not addressed quickly.

      If the EGR valve is stuck open, this would mean exhaust gas is entering the combustion chamber, even when it shouldn’t be. This would raise intake temperatures and reduce power.

      It would be best to take your vehicle to a mechanic you trust to have it checked out in person. You could also try out our ask a mechanic page: https://cartreatments.com/ask-a-mechanic/

      Reply
  2. i have an 08 e350 wagon and it goes into limp mode without hesitation it has problems where it shutters when i go 25% throttle and its “happy” range is 2350-3500RPM where the car runs fine. on the highway ive noticed that the rpms do a “dance” of about 100rpm by that i mean it will jump from 2500 to 2600rpm for no reason on the highway. my mechanic has recommended that i replace the coils and spark plugs and said that it could be the torque converter or the transmission need replacing. any predictions on what it could be?

    Reply
    • I agree with your mechanic that the ignition system is a likely cause. I would change the spark plugs and consider changing the coils if necessary. Try to test the coils before replacing if you can, as they can be a bit spendy on some cars.

      In general, it’s best to change one thing at a time and start with the cheapest stuff first. Always test suspect systems when you can, so you don’t end up throwing parts at it and spending more than you have to.

      Reply
      • I have a 1994 Oldsmoble Cutlass Supreme S 3.1lt 4 door and about 5 weeks ago, I was driving my car in the morning & everything was find,but later on that evening it was driving like it had NO POWER,which I thought that my gas filter was clogged,which I had a new one put on & they tigthen up leading up to the my air filter box.they told me that the reasoning was that I needed an ignition coil,plugs.Took it over to Firestone and it was confirmed that it needed that also an ignition module and some plugs which cost $536.69,NO LABOR would be charged.So is that a good deal? Could it be done cheaper?

        Reply
        • Cheaper is not always better. I’m not sure if it’s a good deal. Ignition coils are expensive, so it sounds plausible to me.

    • I would replace them all at once if they are older and you are having an issue with one of them.

      Ignition coils often wear with use. The greater the engine speed, the faster the wear. If they are all the same age and one of the coils wore out, I would expect the others to not be far behind.

      Reply
  3. I have a 2004 Chevy Silverado 6.0 k2500 and it starts fine and runs fine for about the first 5 miles then a message comes across saying reduced engine power and starts running really rough and wont accelerate but if you shut the engine off for about 5 minutes it runs fine for about another 5 to 10 miles and starts doing it again! What could be causing this?

    Reply
  4. I have a 2011 Chevy Traverse has 126,000 miles on it and when I start it up sometimes it sputters to start like barely no power. Every so often it stalls right after starting, as well as a small pop or tick sound when starting only when started while the engine is hot. No check engine light good fuel pump, alternator and starter are good, had a tune up spark plugs should be good, fluids are good and battery is giving off good voltage.

    Reply
    • Any check engine lights? I wouldn’t assume the spark plugs are good. I would start at the ignition system (with the spark plugs) since that’s cheapest and easiest to fix. Assuming the ignition system is good, test the fuel system to make sure you’re getting enough fuel.

      Reply
  5. It is a wonderful blog post. Here, I have made a conflict between points 5 and 7. I found it the same. Could you please make me clear?

    Thanks

    Reply
    • Engine jerking or rough idle could mean misfires that cause the engine to deliver power unevenly. An engine that is hard to start may crank for a long time before starting, or may fail to start entirely the first few times.

      Reply

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