How do you change spark plugs on Volvo 850?

To change the spark plugs on a Volvo 850, first, ensure the engine is cool and disconnect the negative battery terminal. Remove the ignition coil packs or spark plug wires carefully, then use a spark plug socket and ratchet to unscrew the old spark plugs. Inspect the new plugs, gap them to the manufacturer's specifications if necessary, and install them by threading them in hand-tight before using the ratchet. Reconnect the ignition components and the battery terminal to complete the process.