In my OBD-II cars, none of which are Volvos, I use a ScanGauge that's semi-permanently mounted and stays plugged into my OBD port full time except for if someone else wants to plug in. I use a product called "Blend Mount" that mounts it cleanly.

I can scan on the fly, get my codes, and clear them. No charge, no trip to the auto parts store, no app required, no phone required, and it adds all kinds of gauges that aren't on my cluster as well as fuel economy, etc.

They're not for everyone, but I love mine.
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A bottle of oil and some basic tools in the trunk. The highway is calling. Always remember the difference between durability and reliability. Embrace the old Volvo in your driveway. She's eager to please and, with a little TLC (and a few headaches), sh