My electric driveway gates open and close but not completely. The power switches off before they close or open fully

Does it have a power lift gate ? Do you know anything about automotive electrical systems ? How to use a wiring diagram along with a digital volt ohmmeter to test electrical circuits . ?
Power Liftgate
The power liftgate feature will allow the customer to automatically open or close the liftgate by activating the interior open/close switch, the remote keyless entry transmitter, or by manually initiating liftgate movement. The power liftgate uses a power cinch system to latch the liftgate.
The power liftgate system consists of:

• Power liftgate control switch (located in the overhead console)
• Power liftgate motors (located in the rear headliner area)
• Optical sensor and power liftgate encoder wheel (located in the left power liftgate motor assembly)
• Pinch strip switches (located on the body by the liftgate)
• Home position switch (located on the cinch actuator)
• Forkbolt switch (located on the cinching latch assembly)
• Detent switch (located on the cinching latch assembly)
• Liftgate close chime module (located in a unit external from the power liftgate module)

The forkbolt and detent switch are located on the cinch latch assembly and the home position switch is located on the cinch actuator assembly. For information on removal of the latch or cinch actuator assembly, refer to Section 501-14 .
The power liftgate may not operate under the following conditions:

• a low voltage or dead battery.
• a disconnected battery.
• a power liftgate that has been left open for more than six hours.
• a power liftgate that has been manually closed and left ajar.

If any of these conditions has occurred, the power liftgate must be reset before performing any pinpoint tests. For additional information, refer to Power Liftgate Initialization .

Power Liftgate Initialization NOTE: If the power liftgate system is turned OFF in the message center, the system cannot be activated with any switches or with the liftgate handle. The system will need to be turned ON for any power operation to occur.
NOTE: The power liftgate may not operate under the following conditions:

• a low voltage or dead battery.
• a disconnected battery
• a power liftgate that has been left open for more than six hours.
• a power liftgate that has been manually closed and left ajar.

If any of these conditions has occurred, the power liftgate must be reset.

1. Manually close and fully latch the power liftgate.

1. NOTE: If the power liftgate does not open during this step, refer to the symptom chart to diagnose the power liftgate for no operation. Power open the power liftgate by using the keyfob or overhead console switch.

1. Once the power liftgate is fully open, close the power liftgate by using the keyfob or overhead console switch.
2. your best bet mite be to have a qualified repair shop check it out .

Replace batteries or clean electrical terminals with vinegar/water mixture to receive max power.

on the shaft that controls the arm or gear for the gate movement there will be 2 cams
open the gate and then loosen of one cam and adjust it off the micro switch until the gate is fully open
lightly tension the screw and then close the gate
repeat the adjusting on the second cam until the gate is fully closed
tension up the screw and then using the remote open the gate when it is fully open leave it or in it is not make small adjustment to get it open
press the remote to close the gate and again adjust to properly close the gate

Be sure nothing like a floor mat or tarp/blanket is over the "load to here" line marked at bottom of rear floor latch area. Also could be a micro switch going bad inside the power door operating mechanism. It has 2 of these. One lets it know when lift gate is fully open and the other shuts off motor and light on dash when fully closed and latched. A plastic sliding point rides the mechanism rail and pushes the micro switch. Or the micro switch has worn or dirty contacts inside of it making it work intermittently. Also the plastic slide point could be worn as to not push the switch in fully at contact. Not an easy fix. You have to remove the interior panels on right rear of vehicle and closely watch it operate to locate these switch points.

Power Liftgate
The power liftgate feature will allow the customer to automatically OPEN or CLOSE the liftgate by activating the interior open/close switch, the remote keyless entry transmitter or by manually initiating liftgate movement. The power liftgate uses a power cinch system to latch the liftgate.
The power liftgate system consists of the following:

• Power liftgate control switch (located in the overhead console)
• Power liftgate motors (located in the rear headliner area)
• Optical sensor and power liftgate encoder wheel (located in the left power liftgate motor assembly)
• Pinch strip switches (located on the body by the liftgate)
• Home position switch (located on the cinch actuator)
• Forkbolt switch (located on the cinching latch assembly)
• Detent switch (located on the cinching latch assembly)
• Liftgate close chime module (located in a unit external from the power liftgate module)
• There are a lot of electrical switches an motors
• Visual Inspection Chart Mechanical Electrical
  • Power liftgate motors
  • Power cinching latch and linkage
  • Power liftgate pinch strip switches
  • Liftgate and liftgate hinges
  • Liftgate assist cylinders
  • Liftgate strikers
  • Exterior release handle and linkage
  • Liftgate weatherstrip
  • Liftgate alignment to body and striker
  • Central junction box (CJB) fuse:
    • 5 (7.5A)
    • 105 (30A)
  • Power liftgate control switch
  • Wiring harness
  • Connectors
  Are you willing to take the back hatch apart to test this ,to find a fix . But first have it check for DTC'S - diagnostic troulbe codes '
• Power Liftgate Module Diagnostic Trouble Code (DTC) Index
  Power Liftgate Module Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1342 ECU Is Defective Power Liftgate Module INSTALL a new power liftgate module. REFER to Power Liftgate Module in this section. B2477 Module Configuration Failure Power Liftgate Module REFER to Section 418-01 . B2522 Vbatt1 Circuit Failure Power Liftgate Module Go To Pinpoint Test B . B2552 Vbatt2 Circuit Open Power Liftgate Module Go To Pinpoint Test B . B2698 Vbatt2 Circuit Failure Power Liftgate Module Go To Pinpoint Test B . B2699 Left Pinch Strip Open or Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2700 Right Pinch Strip Open or Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2701 Left Pinch Strip Stuck Active Power Liftgate Module Go To Pinpoint Test B . B2702 Right Pinch Strip Stuck Active Power Liftgate Module Go To Pinpoint Test B . B2703 Open/Close Switch Stuck Active Power Liftgate Module Go To Pinpoint Test B . B2704 Optical Sensor Power Short to Ground Power Liftgate Module Go To Pinpoint Test B . B2705 Optical Sensor 1 Input Not Active During Powered Gate Movement Power Liftgate Module Go To Pinpoint Test B . B2706 Optical Sensor 2 Input Not Active During Powered Gate Movement Power Liftgate Module Go To Pinpoint Test B . B2709 Gate Open Output Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2710 Gate Close Output Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2711 Gate Open Output Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2712 Gate Close Output Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2713 Unlatch Output Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2714 Uncinch Output Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2715 Cinch Output Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2718 Gate Ajar Output Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2721 Gate Ajar Output Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2722 Open/Close Switch Active During Self-Test Power Liftgate Module Go To Pinpoint Test B . B2723 Glass Position Switch Active During Self-Test Power Liftgate Module Go To Pinpoint Test B . B2724 Forkbolt Switch Invalid During Self-Test Power Liftgate Module Go To Pinpoint Test B . B2725 Detent Switch Invalid During Self-Test Power Liftgate Module Go To Pinpoint Test B . B2726 Home Switch Invalid During Self-Test Power Liftgate Module Go To Pinpoint Test B . B2819 Gate Motor Circuit Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2820 Gate Motor Circuit Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2821 Cincher Motor/Unlatch Actuator Short to Ground or Open Power Liftgate Module Go To Pinpoint Test B . B2822 Cincher Motor/Unlatch Actuator Short to Battery Power Liftgate Module Go To Pinpoint Test B . B2825 Movement Ceased Due to Excess Speed Deviation Power Liftgate Module Go To Pinpoint Test B . B2903 Chime Output Circuit Short to Battery Power Liftgate Module/ Liftgate Chime Module Go To Pinpoint Test C . C1935 Chime Circuit Failure Power Liftgate Module/ Liftgate Chime Module Go To Pinpoint Test C . U1950 UBP Communication BUS Fault UBP Communi- cation REFER to Section 418-00 . U2338 Invalid ACM Message Data Power Liftgate Module REFER to Section 418-00 . U2242 Invalid 4WAS Message Data 4WAS Module REFER to Section 308-07A . U2403 Invalid CSM Message Data Vehicle Security Module REFER to Section 418-00 . U2406 Invalid IC Message Data Instrument Cluster Module REFER to Section 413-01 . U2469 Power Liftgate Disabled By Customer Interface Instrument Cluster Module Turn power liftgate on at message center. U2470 Unexpected Keyfob/Keypad Button Press Power Liftgate Module Go To Pinpoint Test A . U2471 Unexpected PRNDL State Power Liftgate Module REFER to Section 419-10 . U2472 Unexpected IGN State Power Liftgate Module REFER to Section 418-00 . U2473 Unexpected Vehicle Speed Instrument Cluster Module/ Powertrain Control Module REFER to Section 413-01 . U2528 PRNDL Data Mismatch Power Liftgate Module/ Instrument Cluster Module Go To Pinpoint Test D .

The battery in the remote probably needs changing! Check that first

There are switches on both ends of the course of the motor, if one fails it will only work on the side that´s ok. That´s why it opens but do not close.Check it out.

Maybe your key fob needs a new battery !
Power Liftgate Initialization

NOTE:If the power liftgate system is turned OFF in the message center, the system cannot be activated with any switches or with the liftgate handle. The system will need to be turned ON for any power operation to occur.

NOTE:The power liftgate may not operate under the following conditions:

• a low voltage or dead battery.
• a disconnected battery
• a power liftgate that has been left open for more than six hours.
• a power liftgate that has been manually closed and left ajar.

If any of these conditions has occurred, the power liftgate must be reset.

1. Manually close and fully latch the power liftgate.

1. NOTE:If the power liftgate does not open during this step, refer to the symptom chart to diagnose the power liftgate for no operation.
   Power open the power liftgate by using the keyfob or overhead console switch.

1. Once the power liftgate is fully open, close the power liftgate by using the keyfob or overhead console switch.
   This system can also set DTC'S
2. POWER LIFTGATE MODULE DIAGNOSTIC TROUBLE CODE (DTC) INDEX (BODY CLOSURES) 501-03 Body Closures 2004 Expedition/Navigator DIAGNOSIS AND TESTING Procedure revision date: 08/23/2004

   Power Liftgate Module Diagnostic Trouble Code (DTC) Index
   

   Power Liftgate Module Diagnostic Trouble Code (DTC) Index
   
   DTC Description Source Action B1342 ECU Is Defective Power Liftgate Module INSTALL a new power liftgate module. REFER to Power Liftgate Modulein this section. B2477 Module Configuration Failure Power Liftgate Module REFER to Section 418-01. B2522 Vbatt1 Circuit Failure Power Liftgate Module GO to Pinpoint Test B. B2552 Vbatt2 Circuit Open Power Liftgate Module GO to Pinpoint Test B. B2698 Vbatt2 Circuit Failure Power Liftgate Module GO to Pinpoint Test B. B2699 Left Pinch Strip Open Or Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2700 Right Pinch Strip Open Or Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2701 Left Pinch Strip Stuck Active Power Liftgate Module GO to Pinpoint Test B. B2702 Right Pinch Strip Stuck Active Power Liftgate Module GO to Pinpoint Test B. B2703 Open/Close Switch Stuck Active Power Liftgate Module GO to Pinpoint Test B. B2704 Optical Sensor Power Short To Ground Power Liftgate Module GO to Pinpoint Test B. B2705 Optical Sensor 1 Input Not Active During Powered Gate Movement Power Liftgate Module GO to Pinpoint Test B. B2706 Optical Sensor 2 Input Not Active During Powered Gate Movement Power Liftgate Module GO to Pinpoint Test B. B2709 Gate Open Output Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2710 Gate Close Output Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2711 Gate Open Output Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2712 Gate Close Output Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2713 Unlatch Output Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2714 Uncinch Output Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2715 Cinch Output Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2718 Gate Ajar Output Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2721 Gate Ajar Output Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2722 Open/Close Switch Active During Self-Test Power Liftgate Module GO to Pinpoint Test B. B2723 Glass Position Switch Active During Self-Test Power Liftgate Module GO to Pinpoint Test B. B2724 Forkbolt Switch Invalid During Self-Test Power Liftgate Module GO to Pinpoint Test B. B2725 Detent Switch Invalid During Self-Test Power Liftgate Module GO to Pinpoint Test B. B2726 Home Switch Invalid During Self-Test Power Liftgate Module GO to Pinpoint Test B. B2819 Gate Motor Circuit Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2820 Gate Motor Circuit Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2821 Cincher Motor/Unlatch Actuator Short To Ground Or Open Power Liftgate Module GO to Pinpoint Test B. B2822 Cincher Motor/Unlatch Actuator Short To Battery Power Liftgate Module GO to Pinpoint Test B. B2825 Movement Ceased Due To Excess Speed Deviation Power Liftgate Module GO to Pinpoint Test B. B2903 Chime Output Circuit Short To Battery Power Liftgate Module/ Liftgate Chime Module GO to Pinpoint Test C. C1935 Chime Circuit Failure Power Liftgate Module/ Liftgate Chime Module GO to Pinpoint Test C. U1950 UBP Communication BUS Fault UBP Communi cation REFER to Section 418-00. U2338 Invalid ACM Message Data Power Liftgate Module
   

check the shocks, they may be bad

ok, try purchasing a Chilton Manual (NOT a Haynes- it's junk). In it you'll find the complete wiring diagram.