Bad ECU 1.6 8v 1990.

[fixkick]

id bet in a shop , we'd get to step 3 and , fail, (toasted is toasted)
i have repaired only bad outputs
and inputs dont fail,they are protected
I have repaired the blown up 5vdc clamp diode that blows the trace off the PCB, if lucking 5vdc returns, on some , the hybrid is blown up and they dont sell any of the expensive parts seen on this PCB.
PCB is the whole main, printed ciricuit board.
those SIP chips are not sold.
the processor is not sold with suzuki code inside (ROM), so it too can not be replaced.

Backup mode kills the CEL dead, (off or stuck on)
if in backup mode that means the main code running, , does tests, and finds the main program can not run. due to some massive, internal main failure
so the activates a BACKUP chip.
the backup is just to move car out of danger, only. say stuck off road or whatever,

personally I never had a old car like this and not have spare ECU
after all they are not getting any more easy to find, and fixing them many times takes 2 or 3 ECU to make one good one, (parts are not sold, key parts)
this will not get better in time, IMO