I was coming down from Animas Forks in 4L in M3 when the Check Engine and red lightning came on. M1 started flashing and the Hill Descent mode quit.

The scanner couldn't reset the codes, & Going to D put me in limp mode. Buddy I was with said to shut down & open the doors for 30 secs. This reset the lightning symbol, but not the CEL. If I tried to go back into 4L, it all came back and I could not use M mode and D would cycle up to 8th pretty quickly. Not ideal going down hill on the trail.

Was able to keep the lightning symbol off as long as I was in 4H and drove an hour or so that way. CEL on, no 4L, red lightning off.

On the last steep downhill, I tried 4L again, as soon as I shifted into 4L, the CEL went out, red lightning stayed out and everything worked normal in D or M.

Any ideas what happened and what might cause it to come back?

when did you last change the battery? have you ever changed the aux battery underneath the main battery.

the Aux battery is notorious for going bad and then it starts pulling power from the main. eventually it kills the main. but, before that it makes the computer and electronics go haywire.

unless you have some sort of extended warranty, i would look to do the aux bypass and electronic stop/start disable mod.

start with fresh batteries.

They are the OEM batteries still. The Jeep sits most of the Winter with a tender on it. Unless I'm touring with it, it's in the garage.

As much as it was a pain yesterday, not a peep today and I spent at least 2 hours in 4L Manual, and fully locked for nearly an hour and no hint of a problem other than not being able to climb scree on Poughkipsee Gulch near Ouray. <shrugs >

I don't know if this will help but, in my 2020 JLUR, they replaced the rear axle and transfer case somewhere around 8,000 miles on the odometer (as I recall).

The transfer case and rear diff were doing weird automatic shifts/locks after a high speed run in high temps from LA to Vegas. This happened a few weeks after doing some 4L and diff lock driving outside Reno. You might have a similar problem but it might have taken longer to show up.

Original batteries on a 2019. I'd definitely replace them.

It certainly was hotter the day it happened. Rode a lot harder yesterday with 0 issues.

Gonna have it looked at when I get back, but these batteries have been babied relatively speaking.