2019 locks up in reverse

[thd566]

Hello. My 2019 Sport S has locked up four times when backing up in the last six or so months. It’s like backing into a tree or something. It has the 3.6 with eight speed automatic. Did it twice within a week about six months ago. Then did it Christmas Eve. It did it again today.
All four times have been backing down a hill. When it stops, if I push the gas it torques the jeep but won’t go. It doesn’t stall or even bog down the engine. If I shift to drive it will go forward fine. I can then put it in reverse and it will back up fine.
What should I check first?
Thanks for any info.

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[azjl#3]

doors closed?

 

[thd566]

doors closed?

Yes. Doors closed, seatbelts on.

 

[3arl0fBruce]

Do you set your parking brake? Could be that it's not releasing properly. That's also assuming that you're reversing from a parked position.

 

[thd566]

I don’t set my parking brake. Twice it has done it backing out of my driveway. The other two times have been backing up in my parents driveway. Every time has been from a parked position. It has never done it right from the get go. Every time I have backed about ten feet or so then it does it. It’s always been downhill the direction I’m backing. It’s always been wet out. Not actually precipitating, but wet. My driveway is concrete, my parents is gravel.
It doesn’t feel like going into park. And it doesn’t feel like the brakes are applying. It’s very harsh. Literally like hitting a tree.
There is no clicking or grinding noises. No noises at all. When it does it, I have to go forward a few inches, then I can continue to back up and it’s fine. I don’t have to shift to park or anything.

 

[3arl0fBruce]

That sounds suspiciously like some sort of rverse collision avoidance system on the fritz. I don't know what nanny features you have on your Jeep, but I would turn off any of them that address the rear of the vehicle and see if the problem falls to resurface. Might help to narrow down what it could be, or rule it out of it isn't the issue

 

[thd566]

It doesn’t have any of the backup nanny features.

 

[au176]

Yes. Doors closed, seatbelts on.

It definitely sounds like an issue with the "doors off, no seatbelt" permissive circuitry. I've experienced it myself when just trying to back my Jeep into the garage without doors or seatbelts.

At it's most basic- and just an educated guess on my part, since I don't have access to Jeep's engineering info- it works like this:

When you put your transmission into Reverse, the ECM checks:

• is driver's door there and closed? (by monitoring voltage through the door's wiring harness)
• is driver's seatbelt on? (by monitoring voltage at a sensor or switch in the seatbelt housing)

At least one of these two conditions must be met for the ECM to permit the trans to go into Reverse. Since you're wearing your seatbelt, and the door is on, I think the problem is at the other end of this circuit. I think the ECM is probably sending the "all OK" signal to the mechanism that stops you from backing up, and that's where the issue probably is.

I'm not sure how Jeep accomplishes this. My guess is that it's a solenoid or servo that shifts the transmission into "Park", since that is how it acts when you can't back up. IF it's something electro-mechanical like this, AND for safety's sake, the default position is "Park" UNLESS the required conditions are met, a weak solenoid or servo, or bad wiring could be causing your problem.

In my last job, I had full access to wiring diagrams and engineering's Theory of Operations for the machines I used to troubleshoot, and that experience is what I'm basing my post on. I doubt that Stellantis shares that level of detail outside HQ, let alone dealerships.

I wish you the best of luck.

 

[azjl#3]

It doesn’t have any of the backup nanny features.

can you put it in neutral does it still bind? then its a rear or front diff binding or brake issue

 

[thd566]

It doesn’t shift into park. Its still in reverse. I’ve had the doors open and had it do the thing to shift into park. The engine revs when you push the gas. When mine is doing whatever it’s doing, the engine still tries to turn the wheels but can’t.

 

[thd566]

can you put it in neutral does it still bind? then its a rear or front diff binding or brake issue

I have not tried to put it in neutral. I’ll try that next time it does it.

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