How to Measure the Condition of an Ignition Coil?
3 Answers
The testing method for the ignition coil is as follows: 1. Set the vehicle's ignition switch to the "ON" position. Then unplug the ignition coil connector, use one end of the multimeter to measure pin 3 and the other end to measure the ground wire. If the voltage between the pin and the ground wire is around 12V, proceed to the next step; if not, check the wiring. 2. Unplug the ignition coil connector, use one end of the multimeter to measure pin 1 and the other end to measure pin 5# of the ECU to check for any short circuits or open circuits. If any are found, check the wiring; if not, proceed to the next step. 3. Unplug the ignition coil connector, use one end of the multimeter to measure pin 2 and the other end to measure pin 2# of the ECU to check for any short circuits or open circuits. If any are found, check the wiring; if not, proceed to the next step. 4. Use the multimeter to measure whether the resistance of the sensor's primary coil is 0.9Ω. If yes, proceed to the next step; if not, replace the ignition coil. 5. Use the multimeter to measure whether the resistance of the sensor's primary coil is 14.5Ω. If yes, proceed to the next step; if not, replace the ignition coil.
Last time I encountered engine shaking and lack of power during acceleration, I suspected it might be a faulty ignition coil. Measuring it with a multimeter is actually quite simple: First remove the coil and locate the three wires. The primary coil resistance between terminals should be around 0.3 to 1 ohm, while the secondary coil resistance typically ranges between 6000 to 10000 ohms. Significant deviation from these values indicates a problem. It's best to wait for the engine to cool down before performing measurements - safety first. Different vehicle brands may have slightly different resistance standards, so consulting the repair manual is recommended. To be honest, DIY measurements can only provide preliminary judgment. For accurate diagnosis, it's necessary to combine with fault code reading, since coil damage sometimes affects spark plugs and high-tension wires as well.
I find that checking ignition coils is most reliable when done in three steps. First is static testing: use a multimeter to measure coil resistance, with primary coil resistance typically below 1 ohm and secondary coil in the range of several thousand ohms. If you detect an open circuit or significant deviation from these values, the coil is likely faulty. Then comes dynamic testing: observe the ignition waveform while the engine is running—using an oscilloscope for a more professional approach allows you to see if the ignition voltage is within the normal range. Finally, there's the substitution method: replace the suspected coil with a known good one and test. This method is the most straightforward, though it requires having a spare part on hand. As a side note, I remind myself that aging coils can lead to increased fuel consumption and excessive emissions, so it's best to address any abnormalities promptly.
