Nissan Ignition Coil Resistance

The ignition coil, a seemingly simple component, plays a critical role in the smooth and efficient operation of a Nissan's gasoline engine. It's responsible for taking the relatively low voltage from the car's battery (typically 12 volts) and transforming it into the high voltage (thousands of volts) required to create a spark at the spark plug. This spark ignites the air-fuel mixture in the cylinder, initiating combustion and ultimately propelling the vehicle. While modern ignition systems are more sophisticated than their predecessors, the fundamental principle remains the same: induce a high-voltage surge through electromagnetic induction. An important aspect of diagnosing ignition coil issues involves understanding and measuring its resistance.

Understanding Ignition Coil Resistance

Resistance in an ignition coil is essentially the opposition to the flow of electrical current within its windings. A coil consists of two primary windings: the primary winding and the secondary winding. Each winding has a specific number of turns of wire, and each winding has its own inherent resistance. Understanding these resistance values is crucial for diagnosing coil health. Significant deviations from specified resistance values can indicate a fault within the coil itself.

Primary Winding Resistance

The primary winding is the first to receive power from the vehicle's electrical system. It has relatively few turns of thick wire and, consequently, a low resistance value, typically measured in ohms (Ω) or even fractions of an ohm. The exact specification varies depending on the specific Nissan model and engine type. This low resistance allows a large current to flow rapidly through the primary winding when the ignition module switches the circuit on. This rapid current flow is key to creating the magnetic field needed to induce the high-voltage spark.

If the primary resistance is too high, it suggests a possible break in the winding, a loose connection, or corrosion. A resistance that is too low, or close to zero ohms, may indicate a short circuit within the winding.

Secondary Winding Resistance

The secondary winding, on the other hand, has a significantly larger number of turns of very thin wire. This high number of turns is what allows it to produce the high-voltage spark. Due to the length and thinness of the wire, the secondary winding exhibits a much higher resistance than the primary winding, typically measured in kiloohms (kΩ). Again, the precise value is highly dependent on the specific coil and vehicle model.

A high secondary resistance may indicate a break in the winding or excessive corrosion. A low secondary resistance may point to a short circuit between windings, which will reduce the coil's ability to generate a high-voltage spark. A completely open secondary winding (infinite resistance) will prevent any spark generation whatsoever.

Why Measure Ignition Coil Resistance?

Measuring ignition coil resistance is a fundamental diagnostic step when troubleshooting ignition system problems. Some common symptoms of a faulty ignition coil include:

Engine misfires (especially under load)
Rough idling
Reduced fuel economy
Lack of power
Check Engine Light (CEL) illuminated with codes related to misfires or ignition coil faults (e.g., P0300 - P0306, P0350 - P0356)

Resistance measurements can help you pinpoint a malfunctioning coil, saving you time and money on unnecessary parts replacements. Before condemning an ignition coil, always check its resistance against the manufacturer's specifications. These specifications can usually be found in the vehicle's repair manual, online databases, or through automotive diagnostic software.

How to Measure Ignition Coil Resistance

To accurately measure ignition coil resistance, you will need a multimeter. Here's a step-by-step guide:

Safety First: Disconnect the negative terminal of the car battery. This prevents any accidental electrical shocks or damage during the testing process.
Locate the Ignition Coils: Identify the ignition coils. In many modern Nissans, each spark plug has its own dedicated coil (coil-on-plug or COP system). In older systems, a single coil may serve multiple spark plugs through a distributor.
Disconnect the Coil Connector: Disconnect the electrical connector from the ignition coil you want to test. This isolates the coil from the rest of the electrical system.
Set Up the Multimeter: Set your multimeter to the appropriate resistance measurement range. For the primary winding, start with the lowest resistance range (typically 200 ohms or less). For the secondary winding, set the meter to a higher resistance range (typically 20k ohms or more). Some multimeters have an auto-ranging function that will automatically select the appropriate range.
Measure Primary Resistance: Connect the multimeter probes to the two terminals of the primary winding connector on the coil itself (not on the disconnected wiring harness connector). Note the resistance reading displayed on the multimeter.
Measure Secondary Resistance: Connect one multimeter probe to the spark plug terminal on the coil (the one that connects directly to the spark plug) and the other probe to one of the primary winding terminals. Note the resistance reading. Some coil designs may require connecting the second probe to a specific terminal for an accurate secondary resistance measurement; consult the vehicle's repair manual.
Compare to Specifications: Compare the measured resistance values to the manufacturer's specifications for your specific Nissan model and engine.

Interpreting the Results

Here's a general guide to interpreting your resistance measurements:

Resistance within specifications: The coil is likely functioning correctly, though it's not a guarantee. Other factors, such as the coil's ability to handle high voltage or its internal insulation, can still be compromised.
Resistance significantly higher than specifications: Indicates a possible break in the winding or a poor connection.
Resistance significantly lower than specifications: Indicates a possible short circuit within the winding.
Infinite resistance (open circuit): Indicates a complete break in the winding.
Zero resistance (short circuit): Indicates a direct short between windings or terminals.

Important Note: A "good" resistance reading does not guarantee that the coil is 100% functional. It simply means the winding continuity is intact. The coil can still fail under load, producing a weak spark or no spark at all when subjected to the high voltages and temperatures within a running engine. In such cases, further testing, such as using an oscilloscope to observe the spark waveform, might be necessary.

Beyond Resistance: Other Diagnostic Considerations

While resistance testing is a valuable tool, it's not the only way to diagnose ignition coil problems. Other factors to consider include:

Visual Inspection: Check the coil for any visible signs of damage, such as cracks, burns, or corrosion.
Spark Testing: A spark tester can be used to visually confirm the presence and strength of the spark produced by the coil. This is a more direct test of the coil's output.
Oscilloscope Analysis: An oscilloscope can provide a detailed waveform analysis of the ignition coil's primary and secondary circuits, revealing subtle problems that resistance testing might miss. This is the most comprehensive method of diagnosing ignition coil issues.
Swapping Coils: If you suspect a particular coil is faulty, you can try swapping it with a known good coil from another cylinder. If the misfire follows the coil, it confirms that the coil is the problem. Be sure to note any DTC codes to help with diagnostics.
Wiring and Connectors: Always inspect the wiring and connectors leading to the ignition coil for any signs of damage, corrosion, or loose connections. These can also cause ignition problems.

Conclusion

Understanding ignition coil resistance and how to measure it is a valuable skill for any car enthusiast or amateur mechanic. By carefully measuring the resistance of the primary and secondary windings and comparing the results to the manufacturer's specifications, you can gain valuable insight into the health of your Nissan's ignition coils and potentially diagnose and resolve ignition system problems. However, remember that resistance testing is just one piece of the puzzle, and other diagnostic methods may be necessary to pinpoint the root cause of ignition issues. Always consult your vehicle's repair manual for specific procedures and specifications related to your Nissan model.