BMW & Mini Ignition Coil Failure (2011-2021): Diagnosing Misfires in N20, N55, S55 & More

Vehicle Fitment and Coil Quantity

This ignition coil (BMW part number 12138616153) is used across a wide variety of BMW and Mini engines. However, the number of coils your vehicle requires depends on its engine. It is crucial to verify your engine type before purchasing. The initial advice suggesting these coils come from a V12 engine is incorrect; the vehicles listed below use 3, 4, or 6-cylinder engines.

Symptoms of a Failing Ignition Coil

Ignition coil failure is a very common issue on these engines. When a coil starts to fail, it can't deliver the high voltage the spark plug needs, leading to incomplete combustion in one or more cylinders. You will likely experience one or more of the following symptoms:

• Engine Misfires: This is the most common symptom. It can feel like a stutter, hesitation, or jerking from the engine, especially when accelerating or under load.
• Rough Idle: When the car is stopped, the engine may vibrate or shake more than usual as it struggles to run smoothly with a non-firing cylinder.
• Check Engine Light: A misfire will almost always trigger the Check Engine Light. Using an OBD-II scanner will typically show codes from P0300 to P0306. The last digit indicates the cylinder with the fault (e.g., P0304 means a misfire on cylinder 4). A P0300 code indicates random or multiple cylinder misfires.
• Loss of Power: With one cylinder not contributing, the vehicle will feel noticeably sluggish and slow to accelerate.
• Reduced Fuel Economy: The engine's computer may try to compensate for the power loss by injecting more fuel, leading to a drop in your average MPG.
• Difficulty Starting: In cases of multiple coil failures or a completely dead coil, the engine may be difficult to start or may not start at all.

Diagnosing a Faulty Coil

Diagnosing a bad ignition coil is a straightforward process that is easy for most DIY mechanics.

1. Read the Code: Use an OBD-II scanner to identify which cylinder is misfiring. For example, a P0302 code points to cylinder 2.
2. Swap the Coil: The easiest way to confirm a bad coil is to swap it with one from a working cylinder. First, remove the plastic engine cover. The coils are located directly on top of the engine's valve cover. Unplug the electrical connector from the suspect coil (e.g., cylinder 2) and a known good coil (e.g., cylinder 1). Pull both coils straight up to remove them.
3. Move the Suspect Coil: Install the suspected bad coil onto the known good cylinder (cylinder 1) and install the good coil onto the cylinder that was misfiring (cylinder 2). Reconnect the electrical plugs.
4. Re-Scan for Codes: Clear the codes with your scanner, start the engine, and let it run until the check engine light comes back on. Read the codes again. If the code has 'moved' to the new cylinder (e.g., you now have a P0301 code), you have confirmed the ignition coil is faulty. 🎬 See this walkthrough for diagnosing misfires on N55 engines. If the misfire code remains on the original cylinder, the problem is likely the spark plug or, less commonly, the fuel injector.

Buying a Used Ignition Coil: What to Check

While new ignition coils are relatively affordable, a good used OEM coil can be a reliable and cost-effective option. Here’s what to look for when buying used:

• Stick with OEM Brands: The original equipment suppliers for BMW are typically Bosch, Delphi, and Eldor. Forum users and mechanics often report that Delphi and Eldor coils are more reliable and less prone to premature failure than some earlier Bosch versions. A used OEM Delphi coil is often a better choice than a cheap, new, no-name aftermarket part.
• Physical Inspection: Carefully inspect the coil's plastic housing. Look for any cracks, which can allow moisture to enter and cause failure. Check the electrical connector pins for any signs of green or white corrosion. Examine the rubber boot at the bottom for any tears, swelling, or a brittle, dried-out appearance.
• Verify the Part Number: The most current and widely compatible part number is 12138616153 (Delphi equivalent GN10571). This number supersedes many older part numbers. Ensure the part you are buying is a compatible replacement.
• Consider Mileage: Ignition coils are a wear item. While they can last over 100,000 miles, failures are common. If possible, choose a used coil from a lower-mileage vehicle. Given the low cost of new OEM-supplier coils, it is often recommended to replace all coils at once, especially on higher-mileage vehicles or if more than one has failed.

Replacement Cost Comparison

The cost to replace ignition coils can vary significantly depending on the parts you choose and whether you do the work yourself.

Frequently Asked Questions (FAQ)