Liftgate System Diagnosis
Liftgate System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/System Description
The liftgate control module 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 liftgate control module through an input from the liftgate handle switch, the interior liftgate control switch, or the remote keyless entry transmitter, but the liftgate may be manually closed to the primary latched position without the liftgate control module performing the power latch function. The ON/OFF switch in the interior liftgate control switch will enable or disable the power open/close operation of the actuator assembly but will 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 liftgate control module 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 function will only be allowed if certain operating criteria are met. Any of the following may cause the power liftgate not to function:
* Vehicle is not in park
* System voltage is below 10.5 V
* Engine is cranking
* The vehicle doors are locked
* A liftgate control module DTC is set
* Liftgate motor excess current is detected which may be caused by a misaligned liftgate striker
* Interior trim and/or liftgate wedge/bumper misalignment
Whenever the liftgate control module loses power or is disconnected, the ignition must be cycled OFF then ON in order to reactivate the liftgate control module.
An open or shorted accessory wake up ignition circuit between the engine control module and transmission control module will cause the power liftgate to work when the ignition is ON but not work when the ignition is OFF.
Reference Information
Schematic Reference
Liftgate Schematics Liftgate Schematics
Connector End View Reference
Component Connector End Views Connector Views
Description and Operation
Liftgate Description and Operation Liftgate
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Verify the liftgate control module is programmed with the latest software.
• If the software is not the latest, program the liftgate control module with the latest software. Refer to Control Module References Control Module References for liftgate control module replacement, programming and setup.
2. Verify the liftgate control module does not have any current DTCs set.
• If the liftgate control module has current DTCs set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
3. Verify DTC B2494 or B153F is not set as a history DTC.
• If DTC B2494 is set only as history, replace the liftgate control switch-exterior, refer to Liftgate Release Switch Replacement (Except Avalanche and Escalade EXT) Liftgate Release Switch Replacement.
• If DTC B153F is set only as history, replace both liftgate object sensors, refer to Liftgate Side Upper Sensor Replacement (Except Avalanche and EXT Escalade) Service and Repair.
4. Verify the scan tool LGM Disable Switch parameter changes from Inactive to Active pressing and depressing the liftgate Enable/Disable button on the interior liftgate control switch.
• If the parameter does not change, refer to Liftgate Interior Release Open/Close Switch Malfunction - DTC B396C or B396D B396C.
5. Place the interior liftgate control switch to the Disable position.
6. Verify the scan tool LGM Front Control Switch parameter changes between Inactive and Active while pressing and releasing the interior liftgate control switch.
• If the parameter does not change, refer to Liftgate Interior Release Open/Close Switch Malfunction - DTC B396C or B396D B396C.
7. With the liftgate closed, observe the scan tool Liftgate Latch Pawl, Ratchet, and Sector Switch parameters. Each parameter status should be as listed below:
* LGM Latch Pawl Sw. parameter - Inactive
* LGM Latch Ratchet Sw. parameter - Inactive
* LGM Latch Sector Sw. parameter - Inactive
• If not the specified value, refer to Liftgate Latch Switches Malfunction - DTC B153A B153A.
8. Observe the scan tool Liftgate Handle Sw. Status parameter while pressing and releasing the liftgate handle switch. The value should change between Active and Inactive as the switch is pressed and released.
• If the parameter does not change, refer to Liftgate Handle Switch Malfunction - DTC B2494 Liftgate Handle Switch Malfunction.
9. Using either the power door lock switches or the keyless entry transmitter, LOCK all doors then UNLOCK all doors. This will set the liftgate module door lock status to unlock.
10. Verify the liftgate will manually open.
• If the liftgate does not manually open, refer to Liftgate Latch Release/Cinch Malfunction - DTC B2495 Liftgate Latch Release/Cinch Malfunction.
11. With the liftgate open, verify the scan tool Object Detection Sensor Status parameter is 3-3.5 V.
• If not within the specified range, refer to Liftgate Object Sensor Malfunction - DTC B153F B153F.
12. With the liftgate open, verify the scan tool Liftgate Latch Pawl, Ratchet, and Sector Switch parameters are as listed below:
* LGM Latch Pawl Sw. parameter - Active
* LGM Latch Ratchet Sw. parameter - Active
* LGM Latch Sector Sw. parameter - Inactive
• If not the specified value, refer to Liftgate Latch Switches Malfunction - DTC B153A B153A.
13. Observe the scan tool Liftgate Handle Sw. Status parameter while pressing and releasing the liftgate close switch. The value should change between Active and Inactive as the switch is pressed and released.
• If the parameter does not change, refer to Liftgate Handle Switch Malfunction - DTC B2494 Liftgate Handle Switch Malfunction.
14. Observe the scan tool LGM Full Open Switch parameter while manually opening and closing the liftgate. The parameter should change between Active and Inactive as the liftgate opens and closes.
• If the value does not change, refer to Liftgate Full Open Switch Malfunction - DTC B153B B153B.
15. Verify while manually opening and closing the liftgate is in proper aligned with the body bumpers, wedges and striker and there is no binding.
16. Verify that the liftgate will remain at or near the full open position and does not drop down.
• If the liftgate will not remain open or drops, refer to Power Liftgate Sags When Open or Slowly Closes Power Liftgate Sags When Open or Slowly Closes.
17. Verify the scan tool LGM Latch Sector Sw. parameter changes from Inactive to Active then back to Inactive within 10 seconds while the liftgate is being automatically cinched closed.
• If the liftgate cinches close and the parameter does not momentarily change states while cinching, refer to Liftgate Latch Switches Malfunction - DTC B153A B153A.
• If the liftgate does not cinch close, refer to Liftgate Latch Release/Cinch Malfunction - DTC B2495 Liftgate Latch Release/Cinch Malfunction.
18. Liftgate open, select the Enable position on the interior liftgate control switch then activate the power close function. Verify the scan tool LGM Clutch Actuator Cmd. changes from Inactive to Active
• If the parameter does not change, refer to Liftgate Motor Clutch Malfunction - DTC B396B B396B.
19. Activate the power close function of the liftgate.
• If the liftgate does not power close, refer to Liftgate Motor Power Open/Close Malfunction - DTC B396A B396A.
20. Liftgate closed, activate the power open function. Verify the liftgate power opens.
• If the liftgate does not power open, refer to Liftgate Motor Power Open/Close Malfunction - DTC B396A B396A.
21. Verify the liftgate has not been auto reversing un-expectedly.
• If the liftgate has been auto reversing, check both liftgate object sensors for interference or deformity.