wow, no jeep stated. nor what year, nor what engine.
ill not even beg country (exports are diffr)
below is all ways, discounting bulb tests.
i guess you mean the key on only self test fails with CEL?
ok the PCM glows the lamp at key on, to tell you the PCM is happy and that it passes its rudimentry self checks
basically means its alive.
if the lamp fails to glow ? (all ways, i fix ECU so know this)
- power to lamp dead (fuse ) yes fuses can crack (unseen)
- lamp bad, (test it with a battery)
- cluster wiring to lamp bad, or that wire from PCM to lamp bad.
- ECU bad, yes, some bad ECU's can run an engine.
- ECU stuck in backup mode, (think limphome but 2 times worse)
in your case id say bad ECU, or bad wire from ECU to CEL.
no year stated, so is it 1988 with that silly junk RENIX EFI with no working CEL or is the unstated car 1993+ where the CEL started working for the first time?
if 93 or newer, we can connect a scan tool, and scan it.
and see , omg , comms are dead, so ECU is in backup mode.
(backup mode is like lawn mower mode, sure it runs but like crap)
ask? can give vivid details of all modes.....
or comm's is ok, and scans and we see DTCs stored and the CEL status in the scanner says ON,"aka, active CEL"
if it says ON< and is not on, then the wire is bad or the
CEL transistor in the ECU blew up. (common with folks using wrong bulb and overheating this poor transistor) replaced many i have.
there are some facts. and is poorly stated. due to NO YEAR !