Keep battery cables clean. I may add a TVS diode in the
circuit to the ECU and maybe another to protect the
alternator. The day this original scenario occurred was
when I failed to turn off the headlights and discharged the
battery and called a tow truck for a jump start. That should
have been my first clue.
"In modern automotive designs, all on-board electronics are
connected to the battery and the alternator. As indicated in
Figure 2, the output of the alternator is unstable and requires
further conditioning before it can be used to power the vehicle’s
other systems. Currently, most of the alternators have zener
diodes to protect against load dump surges; however, these
are still not sufficient. During the powering or switching of
inductive loads, the battery is disconnected, so that unwanted
spikes or transients are generated. If left uncorrected,
these transients would be transmitted along the power line,
causing individual electronics and sensors to malfunction
or permanently damaging the vehicle’s electronic system, "
https://www.littelfuse.com/~/media/...utomotive_tvs_diodes_application_note.pdf.pdf