Re: 2010 Mountaineer Liftgate Won't Lock
Do you hear the lock motor (actuator) in the rear hatch trying to function? If not, check all fuses and other connections under the hood. If everything is tight, electrical shorts are the worst to find. Most of the time its due to corroded connectors. I would start by pulling the rear panel off and making sure things look OK, even get a voltmeter and test the leads. If you can, try putting a load to the actuator for one second (so as not to burn it out) to see if it will function after disconnecting the wires.
If you hear it, it could be a couple of things. The first, is the actuator is on its way out - its not putting out enough torque to lock/unlock the hatch. The second, is that there might be corrosion on the leads (often rivets) that slide a metal or in many cases, a plastic piece, that the actuator pushes/pulls on to lock/unlock the hatch. I had this problem with my Dodge Durango. Moisture got in and corroded a rivet and a small bolt. I was able to replace the bolt, but with the arm being plastic I dared not to drill out the rivet and reinstall another, as I didn't want to crack the plastic arm.
If you can, search around for a Mountaineer FSM (factory service manual) as it should provide you with the proper wiring diagrams.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!