What an ignition coil does
The coil stores energy in a magnetic field and releases it as a high-voltage pulse when the control system commands a spark event. Modern vehicles commonly use one coil per cylinder, though other arrangements exist.
Test the surrounding system before replacing this component.
- 01ObserveTransforms low-voltage electrical power into a controlled high-voltage spark event.
- 02Check inputsPower, ground, command, mounting, and conditions
- 03ComparePreserve codes and operating data / Inspect the plug, boot, connector, and wiring
- 04Budget30 currencies · USD, CAD, EUR, and GBP preview · full values below · planning onlyComponent$238–$320 USD · per replacement estimate · U.S. national parts-and-labor estimate · Price evidence reviewed 2026-09-23
- CAD CA$335–CA$460
- EUR €210–€290
- GBP £175–£245
- 05DecideReject or support the component cause
- 06VerifyApply the exact repair and recreate the symptom
Where it is located
On many coil-on-plug systems, the coil sits directly above the spark plug. Other engines use coil packs and plug wires. Covers, intake components, or other equipment may obstruct access; confirm the exact layout before disassembly.
Symptoms that may involve a coil
- Misfire under load or at idle
- Flashing or steady check-engine light
- Rough running or hesitation
- Hard starting in some conditions
- Cylinder-specific misfire code
- Visible housing or boot damage
A code such as P0301 identifies a cylinder with detected misfire activity; it does not identify the coil as the failed component.
Testing overview
Preserve code and operating data
Record all codes, freeze-frame conditions, and misfire counters before clearing anything.
Inspect the plug, boot, connector, wiring, and surrounding area
Look for damage, moisture, contamination, loose terminals, or signs of incorrect prior work.
Use a controlled comparison when appropriate
Moving a suspected coil to another cylinder can support diagnosis only when the design, access, and service method allow it. Track what moved and recheck the data.
Verify power, ground, command, and output as required
Use the correct wiring diagram and approved test method. Do not guess terminal functions or pierce wiring indiscriminately.
Common failure modes
Heat and insulation stress can reduce spark energy or create intermittent failure.
Contamination and damaged insulation can allow spark energy to escape along an unintended path.
Power, ground, control, or terminal-tension problems can imitate a failed coil.
Excessive required firing voltage or fluid contamination can stress the coil without being the original cause.
Replacement overview
Once testing identifies the coil, follow the exact access, connector, fastener, boot-treatment, and torque instructions for the vehicle.
This range applies only after testing supports an ignition-coil repair. It is not a diagnosis, part recommendation, or quote.
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- Source 1: Ignition Coil Replacement Cost EstimateSource date 2026-09-03 · Retrieved 2026-09-23