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 diagnosing your ignition coils

The ignition coil (also known as a spark coil) is one of the most important elements of the ignition system used with a gasoline engine. The ignition coil generates an electric charge converting the low voltage into high voltage.  High voltage, which in the final phase is converted by a spark plug into a spark - which ignites the fuel-air mixture accumulated in the combustion chamber.

You could have a problem with your ignition coil if you notice any of the following symptoms:

  • Backfiring
  • Starting problems
  • High fuel consumption
  • Engine misfiring
  • Car stalling

So, how do you go about testing your ignition coils? At Garage Gurus we like to share maintenance tips and tricks, so here’s an easy way to test your COP (Coil on Plug) ignition coils.

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For this maintenance job, you will need:

  • IGT-signal from the car manufacturer
  • Test light
  • Test spark plug
  • Probes or T-pin
  • Multimeter
  • Electrical schema  for the car manufacturer

Removing the ignition coil

The first thing to do is to check whether the key in the ignition switch is in the OFF position.

Then disconnect the plug from the ignition coil . By means of an electrical schema (car  manufactured)  - on which one the electric connector should have power (B+).

Install the test spark plug

The next step is to temporarily install a test spark plug at the end of the ignition coil. Connect the electrical connector to the back, the other part of the test spark plug  connect to the ground (GND)(-) of the engine/vehicle. 

Use the  power tester or  multimeter  to check the battery power supply. 

T-pin connection to the cable located in the connector.

Connection to the positive terminal of the battery (B +) electrical cable.

Then touch it several times to the T-pin.

If you notice sparks on the test spark plug, it means that the ignition coil is working properly

B+ measurements

If you didn’t notice any sparks in the previous step, but the coil is connected to both B+ and ground, then the coil needs to be replaced. Use a multimeter to ensure that everything is correctly connected, and the voltage is in the correct range.

Small reminder:  

( B+)    -  positive  terminal of the  battery
(GND) -  negative  (minus )

Ignition measurements

Replacing your ignition coil

Replacing the coil is straightforward. Simply reverse the method you used to remove the ignition coil.

Important notes

  • Conduct the tests with the ignition on
  • Be careful – this test generates sparks of approximately 25,000 volts
  • Ensure you connect the probe or T-pin to the IGT signal on the back of the connector or you won’t get the correct results
Ignition measurements

Want to know more?

Interested in knowing more about oil filter removal tools? Or another engine maintenance job? Check out our online engine courses by registering in our e-learning platform for free or visit the Garage Gurus YouTube channel.


For informational purposes only. We are not liable for any damages resulting from your reliance on this content