A 2013 Bentley Continental GT rolls into the bay with a P0301 — cylinder one misfire. The owner swears it just started, but the fuel trims tell a different story. Long-term trims are maxed out on both banks, and there’s a faint sulfur smell from the exhaust. You clear the code, swap the coil from cylinder one to cylinder two, and within ten minutes the code moves with it. Classic coil failure. But here’s the thing: if you’d relied on the code alone, you’d have replaced a $40 spark plug and called it a day. The misfire would’ve come back, and the customer would’ve lost another week of driving time.
The Bentley 6.0L W12 is a brutal engine on ignition components. Coil-on-plug designs sit directly above the combustion chamber, subjected to heat soak that cooks the epoxy insulation over time. The OE-spec coil carries part number 079905110N, and the aftermarket has stepped up with options like the OSRAM OS1061 that match the OEM’s electrical characteristics while costing a fraction of what the dealer charges. But before you sell any coil, you need to confirm the failure mode — because on these engines, a failing coil can mimic a fueling issue, and vice versa.
Testing Primary and Secondary Resistance — The Baseline
Pull the coil and grab your multimeter. The primary winding on a W12 coil typically reads between 0.5 and 1.5 ohms. The secondary side — the one feeding the spark plug — should land between 6,000 and 10,000 ohms on a cold coil. These numbers shift with temperature, so don’t panic if you see slight variance. What you’re looking for is a dead short (near zero ohms) or an open circuit (infinite resistance) on either winding. Those are definitive failure points.
Here’s where most techs screw up: they test the coil cold, find acceptable resistance values, and reinstall it. But intermittent misfires — the ones that only happen at 4,000 RPM under load — often don’t show up in a static resistance test. The internal insulation breaks down when the coil heats up or when the engine demands maximum output. That’s why you need a scope, not just a meter.
Scope Waveform Analysis — Reading the Pattern
Connect your scope to the coil’s primary circuit using a low-amp clamp around the power feed, or pick up the signal directly from the driver side. Run the engine at idle and watch the pattern. A healthy coil shows a consistent, square-shaped dwell period followed by a sharp, clean spike when the coil fires. The burn line — the horizontal section after the spike — should be flat and stable, lasting roughly 1.5 to 2 milliseconds.
Now compare that to a failing coil. You’ll see one of three patterns: a shortened burn line (indicating weak spark energy), a jagged burn line with excessive noise (suggesting internal arcing), or a complete absence of the firing spike (the driver isn’t getting signal, or the coil is dead). On the W12, you can scope all twelve coils in about twenty minutes by working through the bank connectors. Do it once, and you’ll have a permanent baseline for this engine family.
The Fix — and the Aftermarket Reality
Once you’ve confirmed the coil is the culprit, you’re looking at replacement. The dealer wants north of $200 per coil for the 079905110N. The OSRAM OS1061 — available at OS1061 | OSRAM Ignition Coil | Fits Bentley | OE# 079905110N — matches the OE specs and fits all Bentley models using this coil design. It’s a direct swap: remove the bolts, pull the coil boot, clean the spark plug well, and press the new unit in. Torque to spec and move on.
Pro Tip: If the customer is keeping the car long-term, replace all twelve coils at once. The W12 is a nightmare to access once the cabin air filters and cowl are in place. Do the job once, charge for the labor, and give them peace of mind.
Common Mistake
Don’t shotgun parts. Replacing all coils without scoping them first is a waste of money and doesn’t solve the root cause if the issue is actually a failing injector or a vacuum leak. The coil test takes ten minutes. The diagnostic story — from code to scope pattern to confirmed failure — is what separates a parts swapper from a technician. The OS1061 is a solid replacement ignition coil for the Bentley, but only install it after the scope confirms the diagnosis.
Your customer will thank you when the misfire stays gone — and your reputation as the guy who actually diagnoses before he replaces will keep the bay busy for years.
Recommended Part: OS1061 – OE-quality aftermarket part, ready to ship.
