Mystified with spills codes and locked in park

[Farmor]

‘20 Gladiator main battery was on its way out. Replaced and it starts but shows all codes stop/ start, service shifter/transmission/antilock. With all that the shifter is locked in place.
Replaced small battery though it still metered good. Now it will start on third try and continues to show messages and will not Scott out of park. Dealer schedule for next week. Hoping to find a solution for the farm before then.

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[Mr._Bill]

Completely disconnect both batteries. Separately charge each one. Make sure none of the battery cables touch metal in the engine bay during the process. Reconnect and test. Check the high current fuse array to make sure it wasn't damaged during one of the battery changes.

 

[Farmor]

Completely disconnect both batteries. Separately charge each one. Make sure none of the battery cables touch metal in the engine bay during the process. Reconnect and test. Check the high current fuse array to make sure it wasn't damaged during one of the battery changes.

 

[Farmor]

thank you for the reply. Did as you described to no avail. No signs the fuse array is the problem.

 

[Mr._Bill]

Check all the ground connections, fuses in the box, and inspect the wiring for any visible damage.

It may not be something you can fix.

 

[Farmor]

Mr_Bill, The tow truck guy came up tonight and in the process recognized there were no break lights. We could not find the brake light fuse in the manual/online or the "Mechanics link" he has on his device. We pressed and wiggled all the fuses and not knowing which one it was, the brake lights worked, the jeep started and drove. No where can we find the fuse for the brake lights. Any thoughts - Thank you for your time. BTW, the check engine light remains on, I will ask the dealer to scan and let me know where the signal comes from and find out which fuse is used to protect the brake lights.

 

[Mr._Bill]

I don't know which fuse is for the brake lights. I do know that loose fuses and relays have caused odd problems for many.

 

[ShadowsPapa]

‘20 Gladiator main battery was on its way out. Replaced and it starts but shows all codes stop/ start, service shifter/transmission/antilock. With all that the shifter is locked in place.
Replaced small battery though it still metered good. Now it will start on third try and continues to show messages and will not Scott out of park. Dealer schedule for next week. Hoping to find a solution for the farm before then.

How did you replace the small battery? The low risk way through the wheel opening, or the high risk way through the top?
If through the top most of your issues could have been caused by you, meaning troubleshooting may be tough.

If the MIL is on (Malfunction Indicator Light - some call "check engine light) has anyone checked for a code to see why it's on??

As far as I know there's no "brake light fuse" but there is a fuse for external lights - the brake lights are controlled through the ABS controller. So you have a connectivity issue somewhere - makes me wonder if you went in through the top for that aux/small battery - I know people do it but it's a very high risk way to do it as far as electrical gremlins later, especially for those who aren't fully up on how these are wired and operate.

If you didn't charge both batteries before installing them, that can be a problem, especially if you put the main/large battery in and didn't let the IBS sit disconnected for 20 seconds or so to reset it for the new battery.

Anyway, as there's no brake light fuse on its own - you've got other connection issues going on, probably caused when you swapped out the batteries.
And if you did the battery swap without separating the two ground wires from each other and making sure they could not touch anything while swapping the battery, it's still possible that high current fuse is a problem. You can't know unless you pull and test every leg of that fuse.

 

[Farmor]

Thank you for the reply.
The problem started before the battery changeout. The main battery was at 11.5V
Bought Jeep new in 2020.
I went through the fender to change the start/stop battery. Both batteries were fully charged before installing. Disconnected both batteries, 1st the negatives and then the positives, removed them. Charged both new and installed again hooking positives up first then negatives.
Dealer checked codes found the ABS was off line. checked fuses and power all to be good. ABS had high resistance on the left fender ground, found it a little loose, cleaned and tightened it up and sent it home.
Jeep sat overnight started and all the symptoms returned. Starts on fourth try and runs, will not go into gear and spills all codes for shifter, starts/stop, service shifter - the list goes on. Jeep has been returned to dealer as none of the local mechanics (6) have the correct code reader and these symptoms all point (local mechanics) to the PCM Module.
I have called other dealers looking to see if they have experienced anything like this and they have not. I have ask Jeep to open a case on this problem.

 

[ShadowsPapa]

My bet is none of the "local mechanics" are up to date on things enough to even know what they were looking at if they could read the codes.
And if they can't read the specific codes you are seeing, it means they aren't standard codes and specific to Stellantis (could date back to the Daimler/Chrysler days when no one could read the Jeep WJ ABS codes because they were Mercedes specific)
When you have issues like this - sorry, I'm not sure I'd even bother with a "local mechanic". Things are pretty specialized and unless they have the ability to read and program and the technical documents, they'll be left out in the cold.
A brake job, wheel bearings, pinion seal, yeah, but not this deep.
I'll add to that bet - some dealers would be scratching their heads, too, as this isn't your run of the mill misfire code or ABS code.

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