Spark plug and ignition coil

Ignition coils are replaced when one fails. They are not replaced as a maintenance item. The Engine Computer will detect which cylinder is misfiring when there is a misfire. If your engine uses one "coil-on-plug" for each spark plug, to determine if the ignition coil is the cause, switch it with one from another cylinder, erase the fault code, then see if a new misfire code sets for the cylinder you moved the suspect coil to.

Phew, you just saved me $130+ thank you so much!
Follow up question tho, if you dont mind. What happens when it fails? Would i be stranded?

Nope. Assuming you have four, six, or eight individual coils, a failed one will cause a single-cylinder misfire. The engine will run on the remaining cylinders. The unburned air and raw fuel will go into the exhaust system where it will burn in the catalytic converter and overheat it. That too will be detected and the Check Engine light will be flashing. A flashing light means you're supposed to stop the engine as soon as you can do so safely to prevent that costly damage. If that happens, let the engine cool down for 15 - 20 minutes, then you can restart it and drive for a short distance again.

Yet another thing I didn't know! Thanks for all the great information!