Ignition Coil Diagnostics & Replacement
Ignition coils transform your vehicle's 12-volt battery power into the tens of thousands of volts needed to fire each spark plug. When a coil fails, the cylinder it serves misfires — and a misfiring engine runs rough, loses power, burns more fuel, and can cause serious damage to the catalytic converter. At Dobbs Tire & Auto Centers, our ASE-certified technicians have been diagnosing and servicing ignition systems since 1976. With 150+ locations across the Midwest and South and simple online scheduling, coil service is straightforward and convenient.
Ignition coil failure is one of the most common causes of a check engine light with misfire codes. Schedule your diagnostic appointment today — financing is available.
What Does an Ignition Coil Do?
An ignition coil is a type of electrical transformer. It receives a low-voltage pulse from the engine control module and steps it up to a high-voltage spark that jumps across the spark plug gap to ignite the air-fuel mixture. Modern coil-on-plug (COP) systems use one coil per cylinder, mounted directly on the spark plug. Older systems used a single coil connected to a distributor, while waste spark systems use one coil per pair of cylinders.
Coils fail due to heat exposure, vibration, electrical stress, and voltage spikes — often caused by worn spark plugs that require the coil to work harder. Replacing spark plugs at the recommended interval reduces the electrical load on coils and extends their service life.
Ignition Coil Services We Offer
Misfire Diagnostics & Coil Testing
When a misfire code appears, our technicians use professional scan tools to identify which cylinder is affected, then test the corresponding coil with resistance checks and swap testing to confirm whether the coil, the plug, or the injector is the fault source.
Individual Coil Replacement
Once a faulty coil is confirmed, we will replace it with a quality OEM-equivalent unit. Because COP coils are individual components, replacing just the failed coil is often the appropriate approach — though we'll note if multiple coils show borderline readings.
Coil Boot Replacement
Many COP coil assemblies include a rubber boot that seals the coil to the spark plug well. Cracked or damaged boots can cause arcing and misfires even when the coil itself is functional. Boot replacement is a cost-effective solution when the coil is intact, but the boot has failed.
Spark Plug Replacement with Coil Service
We strongly recommend replacing spark plugs whenever coils are replaced. Worn plugs cause coils to work harder, contribute to coil failure, and reduce combustion efficiency. A fresh plug and coil in each cylinder restores full ignition performance.
Why Prompt Ignition Coil Service Matters
- An active misfire sends unburned fuel into the exhaust stream, which can rapidly overheat and destroy the catalytic converter.
- Misfires reduce power and fuel economy, and the engine may feel rough or shake at idle.
- Running with one misfiring cylinder puts additional load on the remaining coils, accelerating wear.
- Worn spark plugs force coils to generate higher voltages to fire the plug, shortening coil life significantly.
- Early coil replacement is a fraction of the cost of catalytic converter replacement caused by ignored misfires.
What to Expect at Dobbs
Coil service at Dobbs starts with diagnostic scanning to identify the misfiring cylinder. Our technician will then isolate the coil, plug, or injector as the cause through a systematic testing process. We'll explain the findings before proceeding with any replacement. After the repair, we clear fault codes and test-drive the vehicle to confirm the misfire is resolved. A digital vehicle inspection is included, and financing is available if multiple coils or other repairs are needed.
Schedule Your Service Today
Don't ignore a misfire. Schedule an ignition coil diagnostic at any of Dobbs' 150+ locations and let our ASE-certified team restore smooth, efficient engine performance before the catalytic converter pays the price.
Engine misfires (rough or stuttering acceleration), check engine light with specific cylinder misfire codes (P030X), hard starting, rough idle, and reduced fuel economy are all common symptoms.
