Tailgate sensor The panel says the liftgate is open but it is not open and at night the alarm goes off and in the morning the battery is drained. The inside lights used to not go off.Would disconnecting the battery keep the battery from being drained overnight and what could be the cause of this happening?

Power Liftgate System Components
• Liftgate motor assembly
• Liftgate latch
• Liftgate module (LGM)
• Liftgate side upper sensor - left
• Liftgate side upper sensor - right
• Liftgate handle switch
• Liftgate close switch
• GMLAN serial data link
• PWR LIFT GATE 30 amp fuse
• PLG 10 amp mini-fuse

Power Liftgate System Description
Liftgate Module
The liftgate module controls the liftgate motor, liftgate clutch, and liftgate latch based on various inputs. The liftgate module also performs diagnostics on these inputs and outputs and will disable liftgate functionality and set DTCs should a fault be detected. The liftgate module is secured to the motor assembly at the left rear of the vehicle. The module requires a liftgate position learn procedure be performed when replacing. This allows the module to learn the full open and full closed positions of the liftgate.

Location - fuse block right rear
Fuse Block - Right Rear
In the passenger compartment, near the right side of the rear seat cushion under the carpet

Would think it’s on the bottom of the tailgate behind the door panels . The switch will need to connect with a metal pad somewhere near the rear of the car.

Probably a sensor ! without hooking up a factory scanner an checking for DTC'S - diagnostic trouble code's couldn't say for sure what the problem is . Your best bet ,take it to a qualified repair shop .
Electronic module involved in the operation of the liftgate .
Object Obstruction Detection
The liftgate control module continuously monitors power liftgate operation and calculates its location and direction of travel using 2 hall effect sensors that are part of the gear motor assembly. The hall effect sensors are 3 wire sensors and are supplied with a 5 volt power circuit, ground and signal circuits from the liftgate control module. The hall effect sensor signal circuits are referenced from battery voltage within the liftgate control module and pulsed low by the hall effect sensors.
The power liftgate system uses a secondary object detection method which consists of object sensors fixed to both sides of the liftgate near the seal area. The object sensors consist of an internal fixed resistor and normally open switch contacts which when closed will bypass the resistor. The signal circuit is supplied 5 volts through a resistor and monitored within the liftgate control module, and during normal power liftgate operation the signal circuit should remain a fixed value. When an object presses one of the sensors the contacts close and the resistor is bypassed causing the signal circuit voltage at the module to go low.

DTC B1019
DTC B1023
DTC B153A
DTC B153B
DTC B153E
DTC B153F
DTC B2494
DTC B2495
DTC B3130
DTC B3135
DTC B3265
DTC B396A
DTC B396B
DTC B396F
DTC B1019
Circuit/System Description
When calibrating the liftgate position, the liftgate module (LGM) is placed in a functional state to learn the liftgate travel limits. DTC B1019 00 will set automatically as an indicator that the system is in learn mode and not as a fault indicator. Once the travel limits are learned by the liftgate module, the LGM will exit calibration mode. If the LGM does not exit learn mode, DTC B1019 00 will remain current and indicate a fault.
Conditions for Running the DTC

Your liftgate has obstruction sensors, if obstruction is detected in the power mode, the liftgate will reverse. Has a sensor on each side of liftgate. I don't know if replacing sensor/s will fix it, but, that would be my first thought. I hate to see you replace anything and it not fix it.
Your owners manual should give you info on lift gate operation. If you want my diagram for lift gate, holler and I'll post it.

Reset the alarm system lock and unlock all the doors twice.

Operation
A power open or close cycle can only be initiated from the fully closed or open positions while the vehicle is in park and the liftglass ajar switch input to the liftgate module is inactive. At any time during a power open or close cycle the operation can be reversed by pressing any of the open/close switches. The power liftgate can be switched to manual mode with the on/off switch in the overhead console and during manual operation the power latch will still operate. During power liftgate operation the liftgate module continuously monitors the liftgate position and load profile. The position is calculated from hall effect sensor counts and the electrical load of the gear motor is used to determine physical resistance to the liftgate. Both of these profiles must be learned before the liftgate can operate properly and relearned any time most liftgate components are serviced.


Object Obstruction Detection
The liftgate control module continuously monitors power liftgate operation and calculates its location and direction of travel using 2 hall effect sensors that are part of the gear motor assembly. The hall effect sensors are 3 wire sensors and are supplied with a 5 volt power circuit, ground and signal circuits from the liftgate control module. The hall effect sensor signal circuits are referenced from battery voltage within the liftgate control module and pulsed low by the hall effect sensors.
The power liftgate system uses a secondary object detection method which consists of object sensors fixed to both sides of the liftgate near the seal area. The object sensors consist of an internal fixed resistor and normally open switch contacts which when closed will bypass the resistor. The signal circuit is supplied 5 volts through a resistor and monitored within the liftgate control module, and during normal power liftgate operation the signal circuit should remain a fixed value. When an object presses one of the sensors the contacts close and the resistor is bypassed causing the signal circuit voltage at the module to go low.

Gear Motor Assembly
The liftgate motor is a bi-directional motor and open or close operation is the result of the direction of the motor rotation. The liftgate module controls the liftgate motor through the control circuits by suppling power and ground in the appropriate polarity. The motor control circuits are monitored by the liftgate module prior to activation for a high or low condition and during motor operation for any irregular current flow conditions.
The liftgate motor clutch engages or disengages the liftgate motor to the liftgate drive gear and is the component that determines power or manual operation. When the liftgate module supplies power to the clutch control circuit the clutch coil is energized and the liftgate motor is engaged to the liftgate drive gear so that power operation can occur. The liftgate module monitors the clutch control circuit at all times for a short high while in an inactive state or a short low or insufficient current flow while in an active state.
The full open switch is part of the gear motor assembly and will close and become active when the liftgate reaches the full open position. The full open switch signal circuit is supplied battery voltage through a resistor and monitored within the liftgate module. The liftgate provides a low reference circuit and when the switch contacts close the signal circuit goes low and the liftgate module determines the switch to be active.

DTC B153A 00: Liftgate Latch Switch Signal Circuit
DTC B153A 08: Liftgate Latch Switch Signal Circuit Signal Invalid

When calibrating the liftgate position, the liftgate module (LGM) is placed in a functional state to learn the liftgate travel limits. DTC B1019 00 will set automatically as an indicator that the system is in learn mode and not as a fault indicator. Once the travel limits are learned by the liftgate module, the LGM will exit calibration mode. If the LGM does not exit learn mode, DTC B1019 00 will remain current and indicate a fault.
DTC B153B 02: Liftgate Open Switch Signal Circuit Short to Ground
DTC B153B 05: Liftgate Open Switch Signal Circuit Short to Short to Battery or Open
DTC B153E 02: Liftgate Position Sensor Signal Circuit Short to Ground
DTC B153E 05: Liftgate Position Sensor Signal Circuit Short to Battery or Open
DTC B153E 08: Liftgate Position Sensor Signal Circuit Signal Invalid

Your best bet , take it to the dealer .

Remove the liftgate pull handle. Refer to Liftgate Inside Pull Handle Replacement .
DO NOT attempt to remove the liftgate trim panel if there is a failure of the electric latch. Refer to Opening the Liftgate Without Electrical Power .
1
Liftgate Trim Finish Panel
2
Liftgate Trim Finish Retainer Clips (Qty: 2)
3
Liftgate Lower Trim Finish Panel
4
Liftgate Trim Finish Retainer Clips (Qty: 14)

Pretty straight forward.....here are the steps:

Please don't forget to rate--

Rear Window Wiper Motor Removal & Installation To Remove:

1. Disconnect and isolate the negative battery cable.
2. Remove the rear wiper arm.
3. Open the liftgate.
4. Perform the following to remove the liftgate trim panel.
   • If equipped, remove the lift motor link
   • Remove the upper frame molding
   • Remove assist handle screws
   • Disengage the hidden clips around perimeter of liftgate trim
   • Disconnect the electrical connectors.
5. Disconnect the wire connector from the wiper motor.
6. Remove the wiper motor mounting screws.
7. Remove the wiper motor.

To Install:

1. Position the wiper motor in the liftgate.
2. Install the wiper motor mounting screws.
3. Connect the wiring connector.
4. Install the liftgate trim panel.
5. Close the liftgate.

There are 2 switchs one each for the left and right liftgate latch, u must detrim the liftgate to replace them, they stick and cause your problem, replace the courtesy light switches on both latches.