Power Liftgate Malfunction
Power Liftgate Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/System Description
The power liftgate module (PLGM) controls operation of the liftgate latch motor and the liftgate actuator assembly. Under normal conditions the power latch can only be unlatched under power from the PLGM through an input from the liftgate handle switch, the overhead console switch, or the remote keyless entry (RKE) transmitter, but the liftgate may be manually closed to the primary latched position without the PLGM performing the power latch function. The ratchet, pawl, and sector switches are part of the latch motor assembly and are used by the liftgate control module to determine the state of the latch during the process of latching or unlatching. The ratchet and pawl switches will be inactive when the primary and secondary latches are latched, and the sector switch will be active during the power cinch function. The ON/OFF switch in the overhead console will enable or disable the power open/close operation of the actuator assembly and have no effect on power latch operation. The liftgate actuator assembly consists of the actuator drive motor with 2 internal hall effect sensors. The drive motor is mated to a worm type gear off the actuator clutch and when the clutch is engaged the motor rotation is transferred to the clutch gear, intermediate gear, and actuator arm gear. The full open switch is a limit switch mounted on the liftgate actuator assembly along side the actuator arm gear, and will make contact with the cam on the actuator arm gear when the liftgate is near the full open position. The PLGM continuously monitors the liftgate location and direction of travel using the 2 hall effect sensors in the drive motor. The sensor counts are used to determine when the liftgate has reached the open and closed points of travel where the actuator clutch should be disengaged. These positions may vary slightly and must be learned when most liftgate components are serviced.
Diagnostic Aids
Power liftgate operation will only be allowed if certain operating criteria are met. When a power open or close cycle can not be initiated or is aborted during mid cycle, the scan tool open or close history data may be helpful in determining a condition that is preventing liftgate operation. The following is the list of scan tool open and close history parameters and their states that will allow normal operation.
* Crank Signal Present (No)
* Door Lock Status (Unlocked)
* Hall Sensor Feed Status (No Output)
* LGM Latch Fault (No)
* LGM Position Out of Range (No)
* Module Over Current Detected (No)
* Object Detection Sensor Status (Inactive)
* Obstacle Detected in Liftgate (No)
* System Operation Status (OK)
* System Voltage (OK)
* Temperature Out of Range (No)
* Vehicle In Park (Yes)
Circuit/System Verification
1. Ignition ON, verify no SIR DTCs are set.
^ If any SIR DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. Diagnostic Trouble Code Descriptions
2. With the liftgate fully closed and the overhead console power liftgate switch in the OFF position, press the RKE transmitter unlock button 2 times to unlock all doors and deactivate the theft deterrent system.
3. Verify that the liftgate will unlatch when operated from the liftgate handle switch.
^ If the liftgate will not unlatch validate the Liftgate Handle Sw. Status parameter to determine if a switch input or a latch output condition exists.
4. Manually open the liftgate to the full open position and verify that the liftgate opens smoothly without excessive resistance.
^ If excessive resistance or binding occurs in the liftgate travel, disconnect the actuator rod to determine if the actuator assembly or liftgate assembly is the cause.
5. Verify that the liftgate will remain at or near the full open position for several minutes.
^ If the liftgate will not remain open replace the liftgate struts as necessary.
6. Manually close the liftgate to the primary latched position and verify that the latch is properly aligned and will power cinch to the secondary latched position.
^ If the latch does not power cinch to the secondary latched position perform the Power Latch Circuit Test.
7. Verify that the liftgate will power open when the overhead console power liftgate switch is pressed to the ON and OPEN positions.
^ If the liftgate does not unlatch perform the Overhead Console Switch Circuit Test.
^ If the liftgate unlatches but does not open validate the LGM Front Control Switch parameter to determine if a switch input or an actuator output condition exists.
8. Verify that the liftgate will power close from the switch on the bottom of the liftgate.
^ If the liftgate does not power close validate the Liftgate Handle Sw. Status parameter to determine if a switch input or an actuator output condition exists.
Circuit/System Testing
Liftgate Handle Switch Circuit Test
1. Disconnect the harness connector at the liftgate handle switch.
2. Test for less than 1 ohm of resistance between the ground circuit terminal B and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
3. Verify the scan tool Liftgate Handle Sw. Status parameter is Inactive.
^ If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the liftgate control module.
4. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Liftgate Handle Sw. Status parameter is Active.
^ If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the liftgate control module.
5. If all circuits test normal, test or replace the liftgate handle switch.
Liftgate Close Switch Circuit Test
1. Disconnect the harness connector at the liftgate close switch.
2. Test for less than 1 ohm of resistance between the ground circuit terminal A and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
3. Verify the scan tool Liftgate Handle Sw. Status parameter is Inactive.
^ If not the specified value, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the liftgate control module.
4. Install a 3A fused jumper wire between the signal circuit terminal D and ground. Verify the scan tool Liftgate Handle Sw. Status parameter is Active.
^ If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the liftgate control module.
5. If all circuits test normal, test or replace the liftgate close switch.
Overhead Console Switch Circuit Test
1. Disconnect the harness connector at the overhead console switch.
2. Test for less than 1 ohm of resistance between the ground circuit terminal C and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
3. Verify the scan tool LGM Disable Switch parameter is Inactive.
^ If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the liftgate control module.
4. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool LGM Disable Switch parameter is Active.
^ If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the liftgate control module.
5. Verify the scan tool Front Control Switch parameter is Inactive.
^ If not the specified value, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the liftgate control module.
6. Install a 3A fused jumper wire between the signal circuit terminal D and ground. Verify the scan tool Front Control Switch parameter is Active.
^ If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the liftgate control module.
7. If all circuits test normal, test or replace the overhead console switch.
Liftgate Latch Switch Circuit Test
1. Disconnect the liftgate latch connector.
2. Using a DMM, verify that continuity to ground is present at the low reference circuit terminal 2 in the latch harness connector.
^ If the low reference circuit has high resistance to or no continuity to ground, Test the circuit for an open/high resistance. If the circuit tests normal, replace the liftgate control module.
3. Ignition ON, verify that the Pawl Sw., Ratchet Sw., and Sector Sw. scan tool parameters are Inactive.
^ If any of the switch parameters are displayed as Active, test the affected switch signal circuit for a short to ground. If the signal circuit tests normal, replace the liftgate control module.
4. Connect a fused jumper wire from the low reference circuit terminal 2 to the sector switch signal terminal 4 and verify that the sector switch scan tool parameter displays Active.
^ If the scan tool displays Inactive, test the sector switch signal circuit for an open/high resistance. If the circuit tests normal replace the liftgate control module.
5. Connect a fused jumper wire from the low reference circuit terminal 2 to the pawl switch signal terminal 5 and verify that the pawl switch scan tool parameter displays Active.
^ If the scan tool displays Inactive, test the pawl switch signal circuit for an open/high resistance. If the circuit tests normal replace the liftgate control module.
6. Connect a fused jumper wire from the low reference circuit terminal 2 to the ratchet switch signal terminal 6 and verify that the ratchet switch scan tool parameter displays Active.
^ If the scan tool displays Inactive, test the ratchet switch signal circuit for an open/high resistance. If the circuit tests normal replace the liftgate control module.
7. If all the circuits test normal, replace the liftgate latch assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Liftgate Calibration Procedure (Except Avalanche and EXT Escalade)
* Opening the Liftgate Without Electrical Power
* Liftgate Outside Handle Replacement (Except Avalanche and EXT Escalade)
* Liftgate Close Actuator Motor Replacement
* Liftgate Side Upper Sensor Replacement (Except Avalanche and EXT Escalade)
* Liftgate Actuator Switch Replacement
* Liftgate Release Switch Replacement (Except Avalanche and EXT Escalade)
* Liftgate Close Actuator Motor Control Module Replacement (Except Avalanche and EXT Escalade)