As you are here, you must be facing issues with your vehicle. Is your vehicle engine misfiring or stopping abruptly? That could be dangerous, especially amidst the traffic and on highways. If we be honest, it may happen anytime. Therefore, you must know how to test a coil with a multimeter when your car shows signs of improper functioning. It is essential for your safety as well as for the vehicle’s health.
Testing an ignition coil is one of the skills you must learn if you are a regular driver. It will save you from the service center visits for a mere ignition coil replacement. Before letting you know the testing methodology, let us make you familiar with the ignition coil. We will also check out its usage and why it is such an essential element.
What is an Ignition Coil?
The ignition coil is placed in the engine’s Ignition system. It works to convert the battery voltage to a high voltage output. The high voltage that ignition coils generate, is enough to produce a spark for igniting the fuel in the cylinder. Therefore, it is one of the essential auto parts.
The coil wire inside the ignition coil is made of copper. The electricity transferred from the battery is stored as energy in the core of the ignition coil. It is responsible for high voltage. The energy produces the spark when gets transferred to the spark plug present in the cylinder.
The ignition coils connect to the distributor. The other end of the distributor links to the various spark plugs through high tension leads. Such a setup is present in old vehicles, known as the distributor ignition system (DIS).
Besides DIS, there is the coil-on-plug (COP) system. In COP, the ignition coil is directly connected to the spark plug without a distributor, and high tension leads. In this case, there are no spark plug wires leading to the distributor as this system eliminates the use of the distributor.
In COP, the ignition coils directly supply the voltage to the spark plug. Thus, generating spark and igniting fuel rapidly.
Why Is The Importance of Coil Testing?
With a bad ignition coil, your vehicle may suffer severe damages and misfire. With the degradation of coils, the ability to supply voltage decreases. Therefore, spark plugs won’t be able to generate spark and ignite the fuel in a consistent manner. In DIS, it may affect all the cylinders. Whereas in the case of COP, individual cylinder gets affected.
It even reduces the fuel economy. It is due to the incomplete burning of the fuel. Also, as we mentioned above, with bad ignition coils, you may experience problems such as stalling, misfire, no-start, and more. Hence, driving with a bad ignition coil makes you prone to mishappening. You can also check engine lights. Perhaps, even they may not function properly. It exhibits that it is highly essential to test ignition coils if you find symptoms of fault in them.
Tools and Information You Require to Test an Ignition Coil
It is preferred to use a digital multimeter for testing purposes as it can provide you with an accurate reading. However, if you don’t have a digital multimeter, you can use the analog one. Instead of a multimeter, you can also use Ohmmeter and check the resistance reading. With the help of these tools, it is possible to judge whether the ignition coil is fine or not.
Every ignition coil has resistance specifications. Its value varies as per the car model. You can check the car repair manual for getting this information. However, if the repair manual is not present, you can check on the manufacturer’s website. The resistance range is necessary to match the value we obtain after testing.
Hand tools such as Wrench or Ratchet along with Socket Set
Usually, it is not possible to test ignition coils when they are attached to the engine. With the help of a wrench or ratchet, you need to unbolt them. You must have a socket set to unscrew different sizes of nuts. After that, you can place them carefully to start the testing.
How to Test an Ignition Coil with a Digital Multimeter?
Step 1- Take Required Measures Before Testing
Please make sure that the car’s engine is turned off before testing. Also, conducting testing when the engine is warm won’t provide you with the required results. Therefore, provide some time gap between turning off the car and checking. This way, the car engine cools down and come to the proper temperature. Also, wear safety glasses and gloves while you open the car hood and conduct testing.
Before starting with the test procedure, make sure to detach the battery’s negative cable. Please keep it safe, ensuring that it doesn’t come in contact with battery terminals.
Step 2- Locating the Ignition Coil
The accurate location of the ignition coils depends upon the model of the car and ignition systems.
There is a single ignition coil present for the distributor Ignition System. However, in the waste spark ignition system, which is one of the distributor ignition systems, there is one ignition coil per two cylinders. You can spot DIS ignition coils on the left side of the engine compartment. It makes sure that it remains away from the engine heat.
You can find a rectangular or cylindrical assembly having a high tension lead on its end. If you are unable to detect it, try to find the distributor, which is present on the other end of the high tension wire. Follow the wire, and you will find the ignition coil.
It is also possible that the ignition coils are directly attached to the spark plugs. Such an assembly is called coil-on-plug (COP). For detecting the COP ignition coil, you need to find out the cylinder. For each cylinder, there will be a separate ignition coil.
Step 3- Removal of Coil Pack
It is necessary that you remove the coil pack to easily access the terminal points where you need to place the probes. You can use a wrench or ratchet to remove it and unbolt it. Before that, you need to disconnect it from the high tension wire which goes to the distributor. In the case of COP, you need to detach the ignition coil from the spark plug. It could a delicate process. Therefore, make sure that no damage occurs to the spark plug.
It is recommended to check the service manual or ignition control module. It will ensure that no damage occurs while unbolting the pack.
Step 4- Physical Inspection of the Ignition Coil
After you unbolt the coil pack, you will find the ignition coil. Remove the ignition coil from the pack and check its physical condition. It is possible that the bad functioning of the ignition coil is due to dirt and corrosion. If you find any physical damage, there’s no need to go forward to check it using a multimeter. Physical damage signifies that the coil needs to be replaced.
There is a possibility that the damage is caused to the connecting wires. In such a case, replace the wires too. However, to ensure that the fault doesn’t lie in the ignition coil, go forward with the testing.
Step 5- Setting the Range on Digital Multimeter for Testing Ignition Coil’s Primary Winding
There are two types of ignition coil windings: primary and secondary. You need to check the resistance value of the ignition coil’s primary winding. It is available in the repair manual, or you can find it on the manufacturer’s website. Usually, it’s between 0.5 to 2 ohms.
According to that, you need to set the multimeter scale for the resistance test. You can turn the dial on the resistance and select the scale. There are multimeters with auto-scaling features. In such a multimeter, the device itself finds out the range the value lies.
Step 6- Test the Primary Coil
First, you need to touch both the probes of the multimeter with each other. It will detect the internal resistance of the probes. It doesn’t matter much, but it can be helpful in detecting the exact value.
After you touch both the probes with each other, note down the internal resistance. Now, move forward with the testing. Place each probe on either of the electrical poles present on the outer side. Note that there is no issue of the polarity. Therefore, the probes are interchangeable.
Step 7- Test the Results for Primary Windings
Calculate the resistance and subtract the internal resistance of the probes. It will provide you with the exact value. Test, if the practically calculated value is in the range of the mentioned value or not.
- If the practical value in the range of the mentioned value, the primary winding is working fine. You need to deliver your car to the service center for further examination of various parts.
- If the value is lower than the mentioned range, the ignition coil is faulty. It means that there has been a short circuit. Therefore, it needs to be replaced.
- If the value is infinite, the ignition coil is faulty. It is because the circuit is open. Therefore, the resistance would not be finite.
Step 8- Setting the Range on Digital Multimeter for Testing Ignition Coil’s Secondary Winding
The resistance value for primary and secondary coil windings is not the same. You again need to take the help of the service manual. There you will find the range for secondary coil’s resistance.
It is somewhere between 6 kilo-ohms (6,000 kilo-ohms) and 12 kilo-ohms (12,000 ohms). Hence, you need to set the scale for kilo-ohms.
Step 9- Test the Secondary Windings
For the secondary winding, you need to touch one probe to the outer electrical contact and another on the inner electrical contact. Similar to the primary winding, in this also, it doesn’t matter which lead touches which electrical contact.
Note down the reading. In this case, the ignition coil’s secondary winding resistance value is a lot more than internal resistance. Therefore, there is no need to subtract it from the calculated value.
Step 10- Test the Results for Secondary Windings
Now, you need to test that the calculated value is in the mentioned range or not.
- If the value is in the mentioned range, then the secondary coil is also fine.
- In the case of a short circuit, you will receive a value lower than the mentioned range.
- In the case of an open circuit, you will receive a value more than the mentioned range. Therefore, coil needs to be replaced.
Please note that both the primary and secondary coil windings’ resistance value should be in the mentioned range. If any of the two values is not in the range, then the ignition coil is faulty. The process is also known as bench testing.
However, if the value is in the range, you need to visit the service center. There could be a fault in the spark plug wires or any of the other parts.
How to Test an Ignition Coil with an Analog Multimeter?
We do not recommend using an analog multimeter as this method can’t provide an accurate reading. However, if you want to give it a try and don’t have a digital one, go for it. Before going forward with the analog multimeter, follow until step number four, specified while using a digital multimeter.
After you switch off the engine, identify the location, remove and unbolt the coil pack, it’s time to test the coil.
Testing the primary winding
In this case, you need to touch the probes to the outer electrical poles (input terminal and output terminal). The result could be any of these:
- If the pointer shows very high resistance, it suggests that the circuit is open, and the ignition coil is faulty.
- If the pointer shows resistance tending to zero, there could be a possibility of a short circuit.
- If there is minor deflection in the pointer, that suggests some resistance present in the coil.
There could be a judgment error between the second and third cases. The pointer may show only a minute difference between both cases. Also, you won’t be able to find the exact value. That’s the limitation of testing with an analog multimeter. However, if you get resistance as infinity, that will ensure the defect.
Testing the secondary winding
In the case of the secondary winding, you need to touch one lead to either of the outer electrical contact points and the other to the inner electrical point.
- If the pointer shows a finitely high value of resistance, it suggests that the coil is working fine.
- If the pointer shows resistance tending to zero, it means there is a short circuit.
- If the pointer shows very high resistance, it suggests that the circuit is open, and the coil is faulty.
There can be a bit of confusion between 1st and 3rd case. However, in the third case, the pointer will deflect to the other end of the scale. In the first case, it will be somewhat above the other end.
Based on this, we would suggest using a digital multimeter for testing a coil. With the right tools and knowledge, it is very easy how to test a coil with a multimeter.
If you find that the coil is faulty, do not drive your vehicle with it. Instead, replace the coil as soon as possible. After replacing, the coil must generate enough voltage, allow a spark plug to generate spark and ignite fuel.
After replacing it, take the coil pack and place it properly in the engine. Do not forget to connect the wires from the distributor to the ignition coil. If the engine still has a misfire problem, get your spark plugs checked. Also, place the battery’s negative cable at its place. Check engine light and you will know everything is plugged perfectly. Now, you are ready to drive your vehicle without the fear of stalling, misfire, abrupt switching-offs, and low mileage.