There is a specific kind of bug that only shows up when you remove something. Not when you break it, not when you misconfigure it, but when you take it out entirely and discover that it had a second job nobody wrote down.
I spent a few months this year replacing the engine computer in a 2001 Dodge Stratus with a Speeduino DropBear v2, an open-source standalone ECU. I planned it carefully. I mapped every pin. I wrote a note titled “Confirmed so far.” Then I turned the key and got nothing at all.
The answer was three sentences further down in my own notes, in a warning I had written to myself and then argued my way out of.
Continue reading Two Computers, One Engine: The Part of the ECU I Didn’t Know I Was Deleting