System Description

Fig.1 Power Liftgate Introduction:

Fig.2 Key Fob:

POWER LIFTGATE SYSTEM
Some vehicles are equipped with an automatic opening and closing power liftgate system. This power liftgate system is a complex system consisting of many components. Some of these components are the liftgate gear motor assembly, latch assembly, lift gear and rod, liftgate control module, chime/thermistor, full open switch, engage actuator, pinch sensor, liftgate handle switch, overhead console switch, key fob switches, pawl switch and ratchet switch.

The power liftgate system has its own door control module, located on the vehicles left body D-pillar behind the trim panel. (Refer to ELECTRICAL/ ELECTRONIC CONTROL MODULES/DOOR CONTROL MODULE - DESCRIPTION) The power liftgate gear motor assembly is located just above the control module. The latch assembly is located in the bottom center of the power liftgate, below the exterior liftgate handle switch. The power liftgate full open switch, engage actuator, lift gear and rod are part of the liftgate gear motor assembly. The pawl and ratchet switches are part of the latch assembly.

The pinch sensor or sensors are located along the right and left sides of the power liftgate, just above the body line. The liftgate handle switch is an power release switch and is located in the rear light bar assembly just above the license plate. The overhead console switch is an power open and close command switch located in the vehicles overhead console.

Fig.3 Liftgate Fuse Location:

Safety is of the utmost concern with the power liftgate system. Software technology has enabled the power liftgate control module to detect resistance to liftgate travel, which allows the power liftgate to stop and reverse direction anytime an obstruction is felt or any of the command switches are operated (only in closing direction). Battery voltage is supplied to the power liftgate system through a 40 amp fuse, located in the Intelligent Power Module (IPM) assembly. In the unlikely event that the power liftgate system develops a fault the power liftgate can still be operated manually with a key just like a standard manual liftgate.

The power liftgate control module communicates on the J1850 Programmable Communication Interface (PCI) Bus Circuit. Therefore, the power liftgate control module can generate and store its own Diagnostic Trouble Codes (DTC). The vehicles Body Control Module (BCM) receives and supplies messages to the power liftgate control module via the PCI bus circuit. A diagnostic scan tool, such as the DRB III is used to read and troubleshoot these Diagnostic Trouble Codes (DTC). Refer to the Body Diagnostic Manual for a complete list of diagnostic routines.

For additional information refer to Power Liftgate Operation. For a complete system wiring schematic refer to Wiring Diagrams. For system operation instructions refer to the vehicles owner manual.

Refer to the Body section of the service manual for additional information on liftgate components such as the prop rods, hinges, door alignment and striker alignment.

WARNING: BE CERTAIN TO READ ALL WARNINGS AND CAUTIONS (NOTED BELOW) IN POWER LIFTGATE SYSTEM OPERATION BEFORE ATTEMPTING ANY SERVICE OF THE POWER LIFTGATE SYSTEM OR COMPONENTS.

With the push of a power liftgate open/close command switch (key fob or overhead console mounted) a signal is sent out on the J1850 PCI Data Bus circuit. This signal is detected at the body control module (BCM). The BCM then sends a signal out on the J1850 PCI Data Bus circuit to the power liftgate module. The power liftgate module then signals the power liftgate motor to start an open or close cycle, depending on what position the liftgate is in open or closed.

During a liftgate open or close cycle, if the power liftgate module detects sufficient resistance to liftgate travel, such as an obstruction in the liftgates path, the power liftgate control module will immediately stop the liftgate movement and reverse travel to the full open or closed position. The ability for the power liftgate module to detect resistance to liftgate travel is accomplished by hall effect sensors, drive motor speed and pinch sensors (tape switches).

The power liftgate control module has the ability to learn. Anytime the liftgate is opened or closed using the power liftgate system the module learns from its cycle. If a replacement power liftgate component is installed or a liftgate adjustment is made, the module will relearn the effort and/or time required to open or close the door. This learn cycle can be performed with a Diagnostic Scan Tool, such as the DRB III or with a complete cycle of the liftgate, using any one of the command switches. Refer to Standard Procedures in this section for detailed instructions.

The power liftgate system is designed with a number of system inhibitors. These inhibitors are necessary for safety and I or feasibility of the power liftgate system. Refer to power liftgate system inhibitors noted below:

POWER LIFTGATE
The power liftgate (PLG) system is activated through the use of the following: remote keyless entry (RKE), overhead console switches, outside liftgate handle switch or the DRB III. These inputs are hardwired to the body control module (BCM) and can be monitored with a diagnostic tool. The BCM will send the message via PCI bus to the power liftgate module (PLGM). The liftgate must be in the full open or full closed position to operate. Once the BCM sends a button activation message to the PLGM, the module shall read all inputs, outputs and vehicle conditions to determine whether it shall open, close or inhibit the PLG operation. Once the PLGM determines the vehicle conditions are safe for operation, the PLGM will initiate a chime for 2 seconds prior to the liftgate activation and 2 seconds during the open or close cycle.

During an opening or closing cycle, the PLGM can detect an obstacle present should it meet sufficient resistance by the hall effect sensors (integrated in the gear motor assembly GMA).

During an open cycle, multiple liftgate activations (RKE, overhead console, B pillar) are ignored until the liftgate reaches the full open position. However, during a close cycle, a 2nd liftgate activation (RKE, overhead console, B pillar) will reverse the liftgate to the full open position.

If the engine is cranked during a power open/close the PLG will pause then resume after engine cranking. In addition, if the vehicle is placed in gear during an open cycle, the PLG shall reverse direction and begin closing. If the vehicle is placed in gear during a closing cycle, the PLG shall continue closing until fully closed. If the outside handle is activated during an open cycle, the PLG will become a full manual liftgate. If the outside handle is activated during a close cycle, the PLG shall reverse direction of travel to the full open position.

DIAGNOSTIC FEATURES
The PLG can be flashed on vehicle via PCI bus with a DRB III diagnostic tool. The DRB III can read all inputs, actuate all outputs, read module information, and read diagnostic trouble codes. As a reminder, some DTC's can be set during normal PLG operation.

POWER LIFTGATE SYSTEM INHIBITORS
1. The Power Liftgate may not operate in extreme temperatures. These extreme temperatures will be approximately -12 °F (-24.4 °C) on the low side and 143 °F (61.6 °C) for the high side. A chime/thermistor assembly in the rear light bar assembly monitors the outside temperature.
2. The vehicles transmission must be in Park or Neutral for the power liftgate to start a cycle.
3. If multiple obstacles are detected during the same power open or close cycle, the liftgate goes into manual operation.
4. If severe Diagnostic Trouble Codes (DTC) are stored in the power Liftgate Control Module.
5. O/H console lockout will inhibit the B pillar switches only.
6. Liftgate locked will inhibit all interior switches from opening (overhead console). A locked lift-gate can be power closed.
7. Pinch Sensor switch stuck shall inhibit the power close feature.
8. The Power Sliding Door System will not function if battery voltage is too low (below 9.5 volts) or too high (above 16 volts).
9. The Power Sliding Door System will not function if vehicle speed is above 0 mph (0 km/h).