An ignition coil transforms battery voltage into the high-voltage current required to ignite the air-fuel mixture. When performance declines, symptoms may include misfires, difficult starting, reduced power, or increased fuel consumption.
An ignition coil resistance check provides a practical way to assess coil condition using a multimeter. Comparing primary and secondary resistance readings with the vehicle manufacturer’s specifications can help identify internal faults.
Switch off the ignition and disconnect the coil from its electrical connector before testing. Set a digital multimeter to the ohms range, and inspect the coil and terminals for corrosion or physical damage.
Measure primary resistance by placing the probes on the coil’s positive and negative terminals. Then measure secondary resistance between the high-voltage terminal and the appropriate primary terminal, following the vehicle manufacturer’s wiring information.
Compare both readings with the manufacturer’s specifications, because resistance values vary significantly between coil designs. A reading outside the specified range may indicate an open or shorted winding, although a correct reading does not prove that the coil performs properly under operating conditions.
An ignition coil resistance check should be performed with the coil at a similar temperature to the specification. Avoid touching exposed terminals during testing, and replace the coil only after considering related faults such as damaged wiring, poor grounds, or inadequate power supply.