A runaway loco is any working DCC locomotive that has suddenly taken off on its own power and/or you no longer have any control over it.
(This runaway problem is not to be confused with the problem with using 128 Speed Step mode with a decoder that does not support 128 speed step mode.)
This section talks about the what how and why's of locomotive runaways. All runaway events under DCC operation are directly tied to track power when:
1) alternative power is present (DC for example).
2) corruption of the DCC power in the form of unrecognizable DCC commands.
3) hazardous voltages in the form of voltage spikes AS SEEN BY THE DECODER.
Locomotive (Decoder) Runaways fall into 3 categories.
1) Loco takes off on power up or when being placed on the track.
2) Loco is damaged electrically possible right after a derailment.
3) Throttle speed is not in the off state.