How to tell if an ignition coil is bad with a multimeter?

If your vehicle is experiencing issues with starting or running smoothly, a bad ignition coil could be the culprit. Fortunately, you can use a multimeter to quickly diagnose the problem and determine if the ignition coil needs to be replaced. This article will guide you through the steps to test an ignition coil using a multimeter.

What is an Ignition Coil?

An ignition coil is an essential component of a vehicle's ignition system. It is responsible for converting the low-voltage current from the battery into the high-voltage spark needed to ignite the air-fuel mixture in the engine's cylinders. When an ignition coil fails, it can cause a range of problems, including misfiring, rough idling, and difficulty starting the engine.

How to Test an Ignition Coil with a Multimeter

To test an ignition coil with a multimeter, you'll need to follow these steps:

• Locate the ignition coil in your vehicle. It is typically located near the spark plugs or on top of the engine.


• Set your multimeter to the "Ohms" setting, which measures resistance.


• Disconnect the ignition coil from the wiring harness and touch the multimeter's probes to the positive and negative terminals of the coil.


• Check the resistance reading on the multimeter. The resistance should be within the manufacturer's specified range, typically between 0.5 and 5 ohms.


• If the resistance is outside of the specified range, the ignition coil is likely faulty and needs to be replaced.

It's important to note that some ignition coils may have additional terminals or wiring that need to be tested as well. Consult your vehicle's service manual for specific instructions on testing the ignition coil for your make and model.

Additional Ignition Coil Testing Tips

Here are some additional tips to help you accurately diagnose a bad ignition coil:

• Check for any visible signs of damage, such as cracks or burns, on the ignition coil.


• Test the ignition coil's secondary winding by checking for the presence of a high-voltage spark when the engine is cranking.


• If the ignition coil passes the resistance test but the engine is still misfiring, the issue may be with the spark plug or the ignition system's wiring.

By following these steps and using a multimeter, you can quickly and accurately determine if an ignition coil is the source of your vehicle's starting or performance issues.

How do you test ignition coil with multimeter?

To test an ignition coil with a multimeter, first, disconnect the battery and remove the coil. Then, set your multimeter to ohms (Ωcap omegaΩ) and measure the resistance of the primary windings between the positive and negative terminals, expecting a low reading (around 0.40.40.4-222 ohms). Next, measure the secondary windings by touching one probe to the iron core and the other to the spark plug terminal (or metal barb), which should yield a higher reading (typically thousands of ohms). Always compare your readings to the manufacturer's specifications to determine if the coil is functioning correctly.
 
This video demonstrates how to test the primary and secondary windings of an ignition coil: 1mThe AbJ GarageYouTube · Oct 20, 2025
Step 1: Prepare the ignition coil 

• Disconnect the battery: Ensure the power is completely off by disconnecting the vehicle's battery.
• Remove the coil: Take the ignition coil out of the vehicle for testing. 

Step 2: Test the primary windings 

• Set the multimeter: Turn the multimeter to the lowest ohms (Ωcap omegaΩ) setting. An auto-ranging meter will adjust automatically. 
• Connect the probes: Place one probe on the positive (+) terminal and the other on the negative (-) terminal of the coil. Polarity does not matter for this test. 
• Check the reading: The reading should be low, typically between 0.40.40.4 and 222 ohms. A reading of infinite ohms means there is no continuity and the coil is bad. 

This video shows how to measure the primary windings of an ignition coil: 55sFox Can Fix-it GarageYouTube · Mar 19, 2023
Step 3: Test the secondary windings 

• Set the multimeter: Switch the multimeter to a higher resistance range, such as 20,00020 comma 00020,000 ohms (20kΩ20 k cap omega20𝑘Ω), or use an auto-ranging setting. 
• Connect the probes: Touch one probe to the iron core of the coil and the other probe to the metal spring or barb at the top where the spark plug wire connects. 
• Check the reading: The reading will be much higher, usually between 2,5002 comma 5002,500 and 10,00010 comma 00010,000 ohms, depending on the coil type. An "OL" or infinity reading indicates the secondary winding is bad. 

Step 4: Compare to specifications

• Look up the manufacturer's specifications for your specific vehicle to get the correct resistance values for both the primary and secondary windings.
• If the readings are significantly different from the specifications, the coil is likely faulty. 

How do I check if I have a bad ignition coil?

You can check for a bad ignition coil by visually inspecting it for cracks or using a multimeter to test its resistance against the manufacturer's specifications. Another method is to use a spark tester to see if the coil is producing a strong, blue spark while the engine is running; a weak or no spark indicates a faulty coil. 
Diagnostic tests 

• Spark test: Connect a spark tester to the end of the coil, ground the tester, and crank the engine. A strong, blue spark is good; a weak or non-existent spark means the coil is bad. 
• Multimeter test: Disconnect the coil and set your multimeter to measure resistance (ohms). 
  • Measure the resistance across the coil's primary terminals and compare it to your car's manual. 
  • For the secondary winding, measure the resistance between the high-voltage terminal and the primary terminal. A typical range is 6,000 to 15,000 ohms, but this can vary, so check your manual for exact specifications. 
  • If the readings are outside the specified range, the coil is likely faulty. 

Other signs of a bad ignition coil

• Difficulty starting: The engine may be slow to start or not start at all. 
• Misfiring: The engine may feel like it's "stuttering" or running roughly. 
• Reduced fuel efficiency: You may notice a decrease in gas mileage. 
• Poor acceleration: The car may not accelerate as quickly as it should. 
• Check Engine light: An OBD2 scanner can read codes like P030X (misfire) or P035X (ignition coil issue). 

Can OBD2 detect a bad ignition coil?

OBD2 Scanners Can Recognize Ignition Problems
They can also identify problems with ignition coils, spark plugs, and other components via codes such as P035X (ignition coil issues) or P030X (specific cylinder misfires).

How to check if coil is ok or not?

Okay. So if I wanted to go further I can take this. Off. Pull these wires out and this is that. One that's cracked big. Time. Let's see if we can get a secondary resistance coming out of this. So.