I just verified how the SES (cel) light works on my known-good '99 C2500 that's starting faultlessly.
1) Key On to Run position = SES light on steady for as long as I leave it there.
2) SES lights stays on the entire time that the engine is cranking over. (A little flickery, looks like due to voltage variations from the starter working against compression.)
3) A soon as the engine fires, the SES light immediately goes out.
So don't chase the SES light being on while the engine is being cranked over by the starter but has yet to fire.
FWIW --
PS - @slow_c1500 has a valid suggestion. It will only take a second to try, and if it doesn't work we won't bother
to explain the underlying theory. But if it does I have pictures showing why. Let us know if disconnecting the #3
spark plug wire makes a difference.
Hmmm, this sounds suspiciously like the Security feature acting up? Was this a thing back in '96? Or was this added in '98?
For that matter, you are driving a '96, but is it possible a PO swapped in a '98 VCM? Just wondering aloud...
