Do All Four Ignition Coils Need to Be Replaced Together?

[VanNolan]

If only one or two ignition coils are faulty while the others remain unaffected, are in good working condition, and have a service life of less than 100,000 kilometers, it is not necessary to replace all of them. However, if the mileage exceeds 100,000 kilometers, it is advisable to replace all the ignition coils together. Here is some information about ignition coils: 1. The core components of the ignition system are the ignition coil and the switching device. Increasing the energy of the ignition coil allows the spark plug to generate a sufficiently energetic spark, which is a fundamental requirement for the ignition system to adapt to the operation of modern engines. 2. A typical ignition coil contains two sets of windings: the primary coil and the secondary coil. The primary coil is wound with thicker enameled wire, usually around 0.5-1 mm in diameter, with approximately 200-500 turns. The secondary coil is wound with finer enameled wire, typically around 0.1 mm in diameter, with approximately 15,000-25,000 turns. 3. Ignition coils are categorized into open-core and closed-core types based on their magnetic circuits. Traditional ignition coils use an open-core design, with the core made of stacked silicon steel sheets about 0.3 mm thick, around which the primary and secondary coils are wound. Closed-core ignition coils use an I-shaped core for the primary winding, around which the secondary coil is wound, forming a closed magnetic circuit with the core.

[McGavin]

You don't necessarily have to replace all four ignition coils. I've seen many cars that only had a single coil replaced and they ran just fine. The key is to assess the actual condition of the vehicle: if the car is only five or six years old and just one coil has failed while the other three test normal, then simply replacing the faulty one is sufficient. Don't fall for the repair shop's pitch to replace them all—after all, a single coil can cost several hundred dollars. However, it's crucial to use a coil that matches the original specifications for your car. If the new coil's parameters differ significantly from the old ones, it can cause engine shaking and even increase fuel consumption. I once encountered a case where someone opted for a cheaper, mismatched coil, and the car idled so rough it shook like a tractor.

[SawyerAnn]

My suggestion is to make a decision based on the mileage. For example, cars with over 100,000 kilometers usually have aging ignition coils. If you only replace the faulty one at this point, the other three might fail within a few months. Repeated disassembly not only costs more but also risks damaging other components. Last time I replaced them, I had the mechanic test the resistance of the old coils—two were already near their limits. So I replaced all of them, and haven’t had any issues for over two years. It’s similar to changing tires: you don’t have to wait for all four to blow out. If the wear is similar, preventive replacement is much more hassle-free.

[LeonardoRose]

From a maintenance perspective, the key issue is the compatibility between old and new coils. When the engine is running, all four coils must fire synchronously. After 2-3 years of use, the resistance values of old coils will differ from newly purchased ones - even for the same brand. I've encountered cases where replacing just one coil triggered engine fault codes. Diagnostics revealed the new coil had 15% higher ignition energy than the old ones, causing air-fuel ratio imbalance. Nowadays, I always recommend scanning other coils with a diagnostic tool before replacement. If the remaining lifespan is below 30%, or for models prone to coil failures, I'd suggest replacing the entire set. After all, the labor cost for one replacement session could cover half the price of a new coil.