If your scan tool is flashing a P0302 cylinder 2 misfire code, one of the first things worth checking is whether the ignition coil on that cylinder is still within spec. Measuring the primary and secondary resistance of the coil gives you a quick, inexpensive way to confirm or rule out a bad coil before you start swapping parts or chasing wiring problems. A coil that tests outside its resistance range simply cannot fire the spark plug correctly and that leads to misfires, rough idle, poor fuel economy, and potential catalytic converter damage over time.

What Do Primary and Secondary Resistance Specs Actually Mean?

An ignition coil is basically a small transformer. It takes low-voltage battery power on the primary (input) side and converts it into the high-voltage spark on the secondary (output) side. Both windings are made of copper wire, and both have measurable resistance.

Primary resistance is measured between the two low-voltage terminals of the coil (typically the positive and negative pins). This reading is usually very low often between 0.4 and 2.0 ohms, depending on the vehicle.

Secondary resistance is measured between the high-voltage output terminal and one of the primary terminals. This reading is much higher usually between 6,000 and 15,000 ohms (6k–15kΩ) for most coil-on-plug designs, though some older or performance coils can fall outside that range.

When either reading drifts too far above or below the spec, the coil is likely failing. An open winding reads infinite resistance (OL on your meter). A shorted winding reads near zero where it shouldn't. Either way, the coil cannot produce a reliable spark for cylinder 2.

Why Does Cylinder 2 Keep Misfiring?

A P0302 code means the engine control module (ECM) detected an irregularity in the combustion events on cylinder 2. The coil is a common suspect, but it isn't the only one. Before assuming the coil is bad, it helps to understand what else can trigger the same code:

• Fouled or worn spark plug A damaged plug forces the coil to work harder and can mimic coil failure.
• Wiring or connector issue Corroded pins or broken wires at the coil harness interrupt signal delivery.
• Fuel injector problem A clogged or stuck injector on cylinder 2 causes a lean or rich misfire unrelated to ignition.
• Low compression Worn rings, leaking valves, or a head gasket issue on that specific cylinder.
• Vacuum leak near cylinder 2 intake runner Unmetered air leaning out the mixture on one cylinder.

The reason resistance testing matters is that it's the fastest way to narrow the problem down to the coil itself rather than guessing. If the coil tests within spec, you move on to plugs, wires, compression, or fuel without wasting money on a replacement coil you didn't need.

Typical Resistance Ranges by Vehicle Type

Exact specifications vary by manufacturer, coil design, and model year. The table below covers common ranges, but always check the service manual for your specific vehicle.

• Toyota / Lexus (coil-on-plug, 4-cylinder) Primary: 0.6–0.9 Ω, Secondary: 8,000–12,000 Ω
• Honda / Acura Primary: 0.6–0.8 Ω, Secondary: 7,500–12,500 Ω
• Ford (3.5L, 3.7L V6 COP) Primary: 0.5–1.5 Ω, Secondary: 6,500–11,500 Ω
• GM (5.3L, 6.0L V8) Primary: 0.5–0.9 Ω, Secondary: 5,500–8,500 Ω
• Nissan / Infiniti Primary: 0.7–1.0 Ω, Secondary: 8,000–14,000 Ω
• European (BMW, VW, Audi direct ignition) Primary: 0.3–0.7 Ω, Secondary: 6,000–10,000 Ω

These are ballpark ranges gathered from common service data. Your vehicle's actual spec could differ, especially if it uses a coil with an integrated igniter or a wasted-spark design. A reliable source for exact numbers is the manufacturer's service manual or a database like AutoZone's repair info.

How to Test the Cylinder 2 Coil Resistance With a Multimeter

You only need a digital multimeter set to the ohms (Ω) function. Here's the process:

1. Disconnect the coil. Remove the electrical connector and pull the coil out of the cylinder 2 well. Refer to your service manual for the location on inline engines, cylinder 2 is usually the second from the front; on V-engines, it depends on the bank numbering.
2. Identify the terminals. Most COP coils have two primary pins (sometimes labeled + and −, or simply pin 1 and pin 2) and one high-voltage tower that connects to the spark plug.
3. Measure primary resistance. Place one meter probe on each primary pin. Record the reading. It should fall within the manufacturer's spec typically under 2 Ω.
4. Measure secondary resistance. Place one probe on one primary pin and the other probe on the high-voltage terminal (inside the boot where the plug sits). Record the reading. It should fall in the thousands of ohms range per spec.
5. Compare to spec. If either reading is outside the range too high, too low, or showing OL (open loop) the coil is bad and should be replaced.

For a more detailed walkthrough with meter setup tips, our guide on how to test ignition coil resistance with a multimeter covers the exact steps with photos and troubleshooting notes.

What If the Coil Tests Good but the Misfire Remains?

A coil that passes resistance testing can still cause problems under load. Resistance testing catches obvious internal failures open windings, shorts, and severe degradation but it doesn't catch every failure mode. Here's what to check next:

• Swap test: Move the cylinder 2 coil to another cylinder and clear the code. If the misfire follows the coil, the coil is bad even though it tested within spec. If the misfire stays on cylinder 2, the coil isn't the problem.
• Spark plug inspection: Pull the plug from cylinder 2 and look for cracks, heavy deposits, worn electrode, or an incorrect gap. Replace if needed.
• Compression test: Low compression on cylinder 2 (below about 100 psi on most engines, or more than 10–15% lower than other cylinders) points to a mechanical issue.
• Injector balance test: A weak or clogged injector won't deliver enough fuel, causing a misfire that the ECM may blame on ignition.

Our comparison of resistance testing versus spark testing for cylinder 2 explains when each method is more useful and how they complement each other.

Common Mistakes When Testing Coil Resistance

Plenty of DIYers and even some shops get misleading resistance readings because of simple errors. Watch out for these:

• Using a low-quality meter. Cheap multimeters struggle with low-ohm readings. The difference between 0.5 Ω and 0.8 Ω matters a meter with poor resolution will blur that line. Use a meter that reads down to 0.1 Ω accurately.
• Not zeroing the meter. Touch your probes together first and note the reading. Subtract that from your coil measurement. Even a 0.2 Ω offset matters on primary readings.
• Testing a hot coil. Resistance changes with temperature. Most specs are for a cold coil (around 68°F / 20°C). Testing a coil that just came off a running engine gives higher readings and false conclusions.
• Ignoring the connector. Corroded or damaged pins at the coil harness connector add resistance to your reading or block signal entirely. Inspect and clean the connector before testing.
• Only testing one winding. Both primary and secondary resistance matter. A coil can pass on one side and fail on the other.

Should You Replace Just the Cylinder 2 Coil or All of Them?

If testing confirms the cylinder 2 coil is out of spec, you have two options:

• Replace only the bad coil. This is the most cost-effective approach, especially on newer vehicles with low mileage. Match the replacement to the OEM part number.
• Replace all coils. If your engine has over 100,000 miles and the coils have never been changed, replacing the full set can prevent repeat failures. Coils age together, and one going bad often means the others aren't far behind.

Either way, replace the spark plugs at the same time if they're due. A fresh coil firing into a worn plug still underperforms.

Quick Checklist for Diagnosing a Cylinder 2 Misfire With Coil Resistance Testing

• ✅ Read the code confirm it's P0302 and note any companion codes (P0300, lean/rich codes)
• ✅ Look up your vehicle's exact primary and secondary resistance specs
• ✅ Remove the cylinder 2 coil and inspect it for cracks, carbon tracking, or oil contamination
• ✅ Measure primary resistance (both pins) compare to spec
• ✅ Measure secondary resistance (pin to tower) compare to spec
• ✅ If out of spec, replace the coil and clear the code
• ✅ If within spec, perform a coil swap test to another cylinder
• ✅ Inspect the spark plug on cylinder 2 for wear or damage
• ✅ Check the coil harness connector for corrosion or loose pins
• ✅ If misfire persists after coil and plug replacement, test compression and injector balance

One practical tip: Record your resistance readings and keep them with your maintenance notes. Tracking coil resistance over time helps you spot degradation before it causes a misfire, especially on high-mileage engines where coils are aging gradually rather than failing suddenly.