Three days later, a wrinkled plastic envelope from Shenzhen arrived. Inside was a device that looked like a shrunken, blue computer mouse with a thick cable sprouting from its tail. Leo felt a spark of hope. He crawled under the steering wheel, found the OBD2 port hidden behind a loose panel, and plugged it in. A small red LED on the device blinked to life.

The check engine light was a small, amber eye staring at Leo from the dashboard, unblinking and accusatory. It had been on for three days, and the car—a 2007 hatchback with more miles than sense—was starting to shudder at stoplights.

Following a YouTube tutorial with only 200 views, Leo opened Device Manager. There it was: a yellow exclamation mark next to "Unknown Device." He forced the driver update, pointed it to the folder, and held his breath.

Leo wasn’t a mechanic. He was a freelance translator who worked from a cramped apartment, surrounded by dictionaries and empty coffee mugs. But he was resourceful. A quick online search pointed him to a cheap solution: a tiny blue ELM327 v1.5 USB interface. "Plug and play," the listing said. "Read and clear engine codes."