[tmerc]

Storage space is limited. There's a black box for accidents that keeps a rolling window of data. That's not the dcm. Outside of that, how much telemetry can you store? What's the retention when there's no cellular connection? And importantly, where is it stored? My guess is that the dcm, having a battery back up and a cellular connection, is also the telemetry store. No evidence other than it's the cheapest and most reliable way to do it.

At least for Subaru, the dcm also connects to all antenna so removing it disconnects gps antenna. For other cars, I'd still expect removing the dcm to be good enough for 95% of people given the current expectation from car companies that no one would want to remove the dcm.

[fc417fc802]

That's an interesting point but consider that bandwidth is also limited when we're talking about an always on system that's in every vehicle sold. And until recently storage was remarkably cheap.

If you log 32 bytes once per second that's only 962 MiB per year uncompressed. But 32 bytes is a lot (or depending on what you're logging not very much), once per second is almost certainly more frequent than necessary, and almost all vehicles spend the vast majority of their time turned off.

For example logging RPM every 100 ms, 8 bits gets you reasonable but not perfect accuracy and you're looking at 300 MiB per year of continuous operation. It's just not much of a storage requirement for quite detailed telemetry.

[aaronbeekay]

Yah, but automakers are very cost-sensitive, and flash memory/NVM is one of the easiest places to penny-pinch. I get crap about 2kB payloads.