P0603 code on ‘98 siville sts. Getting lots of codes, any thoughts on easy fix?
I find this online
P0603 CADILLAC - Control Module Long Term Memory Reset Possible causes
Loose or poor battery terminal connection
Low battery charge
Engine Control Module (ECM) / Powertrain Control Module (PCM) power supply circuit is open or shorted
ECM/PCM Programing
Faulty ECM/PCM
What other codes are you getting?
Diagnostic Trouble Code P0603 is usually caused by a bad ECU.
https://www.troublecodes.net/pcodes/p0603/
Tester