Gate lock with FM350

manual page 34 tells what beep indicates
https://www.mightymule.com/wp-content/uploads/FM350-Mighty-Mule-automatic-gate-openers.pdf

https://www.manualslib.com/manual/770594/Mighty-Mule-350.html
Other manuals below
https://www.mightymule.com/manuals/

video which may help
https://www.youtube.com/watch?v=ceEQcjUrKQM
https://www.youtube.com/watch?v=lic6rQY-yyc
https://www.youtube.com/watch?v=JaddCJBeFIM
https://www.youtube.com/watch?v=SjnWd5SBx7M

Here is how it works !
Liftgate Locking Operation
The lift gate will lock any time the vehicle is shifted out of park on vehicles equipped with an automatic transmission and at vehicle speeds exceeding 5 kph with manual transmission. This happens in conjunction with auto door locks if enabled or independently of auto door locks if the feature is disabled. This ensures that the lift gate is locked anytime the vehicle is shifted out of park or when the vehicle is in motion.
The lift gate lock relay supply and coil sides receive a constant voltage through the battery voltage supply circuit and the ECC fuse. The normally closed contact is connected to ground and the control side is connected to the body control module (BCM). A lock function will occur when a door lock switch activation, keyless entry lock transmission, auto door lock function or a lift gate lock function has been received by the BCM. The BCM will then ground the control side of the lift gate lock relay. This energizes the relay and allows voltage to be applied to the lift gate lock actuator lock control circuit. Since the other side of the lift gate lock actuator is connected to the normally closed contacts of the door unlock relay to ground, the lift gate will lock. When an unlock function occurs the BCM will ground the control side of the unlock relay and the rear doors and lift gate will unlock.
The BCM also runs diagnostics on the lift gate lock relay control circuit and will set DTC B3825 as current and also send a Class 2 message to the DIC. The DIC will display REPLACE LIFTGATE FUSE to inform the driver that a fault has been detected in the lift gate lock circuit and that the lift gate is not locked. Faults that will set the DTC and cause the DIC to display the message could be any of the following:
?€¢
An open ECC fuse

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An open or short to ground in the lift gate lock relay battery positive voltage circuit

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A faulty lift gate lock relay

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An open or short to ground in the lift gate lock relay control circuit

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A short to ground in the lift gate lock actuator lock control circuit

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A faulty BCM

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I have a 2008 Suburban with the power liftgate disabled. I have had the power latch stop working, and the BCM report that the rear access open when it is closed (both gate and glass). Somehow the liftgate module thinks the gate is open, so I cannot open the gate at all, and the latch and rear wiper will not work. To reset the control module I pulled the liftgate fuse (#20) in the instrument panel fuse box, turned the car on, off, reinstalled fuse, turned car on, unlocked doors using drivers side switch, and the power latch will function again - at least for a while.

Have you tried using the key at the tail gate, ,open with the key then move then push the locking mechanism open with a screwdriver the latch close while the door/gate was open, push it back open use some force. Hope this help if is a mechanical issue and not electrical it doesn't matter .

Insert the key and turn the lock cylinder while lifting up on the lift gate. You have to get the gate open. Once open, The strike plate (where the locking mechanism hits) is bolted to the jamb. Loosen the bolts and slightly move it toward the rear of the vehicle. NOT TOO MUCH!
Tighten the bolts, and try it. Hope this helps.

The short answer is yes, something could have bent when that gate was closed with the latch already closed. Look at the latch and make sure it wasn't jammed before you do a full replacement. If the latch is closed use a screw driver to open the latch while using the key to open the gate. Once you get the latch open try closing and locking the gate.

Hello and welcome the problem is very simple to resolve first make sure you have battery power turn off vehicle open rear gate unlock doors go to rear gate and look at lock unlock again and push the Grey plastic lock trigger mechanism forward towards front glass close gate unlock again make sure lock is still in the position you just set it to and close glass it will the lock. Normally what happens in this situation was power was removed from your jeep and the rear gate was opened with no power running to electric lock so it stays in a set position you cannot lock the glass because there was no power in the electric lock I will lock once you reset it Hope this help. Please Rate Me . For further assistance you can always ask me.

Here is a quick try for you that works for me. Push the handle and make sure it is all the way returned to the closed position. Then try the lock, power or key. Then try and open. I have found that if the handle does not return to closed position it will not allow the lock to operate. Hope this helps and have a great day.