Safety Precautions and Preparation

• Park the car on a flat surface and turn off the engine. Ensure the vehicle is in park or gear (for manuals) and the parking brake is engaged.
• Open the hood and allow the engine to cool if it has been running.
• Disconnect the negative (-) battery terminal to prevent electrical short circuits.
• Gather the necessary tools: socket set with an extension, spark plug socket, torque wrench, anti-seize compound (optional), and dielectric grease.
• Refer to the owner’s manual to locate the spark plug specifications.

Remove Engine Cover

• Locate and remove the engine cover. Most Mercedes-Benz models have a plastic cover that can be lifted off or may be secured with screws or clips that require removal.

Access the Ignition Coils

• Identify the ignition coils on the engine. The 2017 Mercedes-Benz C-Class typically includes individual coils mounted directly onto each spark plug.
• Carefully disconnect the electrical connector from each coil by pressing the tab and pulling it away from the coil.
• Use a socket wrench to remove the bolts securing the ignition coils, then gently pull each coil out by twisting slightly if necessary.

Remove Old Spark Plugs

• Use a spark plug socket attached to an extension and ratchet to carefully loosen and remove each spark plug. Make sure to handle them gently to avoid damage to threads in the engine.
• Inspect the old spark plugs to get any indications of engine problems like oil residue or unusual wear patterns.

Install New Spark Plugs

• Check the gap on each new spark plug with a gap gauge and adjust if necessary to match the specification in the owner's manual.
• Optionally, apply a small amount of anti-seize compound on the threads of the new plug to prevent future seizing (be careful not to apply it to the electrodes).
• Screw the new spark plugs by hand to avoid cross-threading, followed by tightening with a spark plug socket and torque wrench according to the manufacturer’s recommended torque settings.

Reconnect Ignition Coils

• Reinstall the ignition coils onto each spark plug by aligning and gently pressing them down.
• Secure each coil with its respective bolt and attach the electrical connector back onto each coil.

Reattach Engine Cover and Battery

• Reattach the engine cover by reversing the removal process.
• Reconnect the negative battery terminal to restore power.

Final Inspection and Testing

• Before starting the engine, recheck that all steps are correctly completed and no tools are left in the engine bay.
• Start the engine to ensure it runs smoothly and check for any irregular idling or misfire indications.

This guide is a general procedure and may not cover every potential issue that can arise. Always refer to your vehicle's service manual for specifics related to your model, or consult a qualified mechanic if unsure.