That is a bit over simplified. In practice more is passed, but for example the ECU ignores based on rules like RPM above X, TCM not in P, and so on. There is pr

That is a bit over simplified. In practice more is passed, but for example the ECU ignores based on rules like RPM above X, TCM not in P, and so on. There is pressure to move to a single high speed bus and modules that pass messages based on priority and time.