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Power Liftgate Malfunction




Power Liftgate Malfunction

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.

Diagnostic Fault Information





Circuit/System Description

The liftgate 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 driver door 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 driver door will enable or disable the power open/close operation of the actuator assembly but will have no effect on power latch operation. The liftgate control module continuously monitors power liftgate operation and calculates its location and direction of travel using 2 inputs from the liftgate position sensor. One input returns the position of the liftgate relative to the latch along the x-axis and the other returns the position of the liftgate relative to the latch along the y-axis. The liftgate control module then uses these 2 inputs together to calculate its angle relative to the liftgate latch.

Diagnostic Aids

Before testing can be performed, the liftgate must be opened. Refer to Opening the Liftgate Without Electrical Power (Procedures) for the appropriate procedure.

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:

* After a power loss of the low current battery supply until the ignition is cycled
* Vehicle is not in park
* Engine cranking is present.
* Ambient temperature at the liftgate must be within -17 to +80°C (+1 to +176°F).
* Liftgate motor excess current is detected.
* System voltage is out of range.
* A DTC is set that disables power liftgate functionality.
* The liftgate is locked when attempting to open from exterior handle.

Inspect the system for proper fluid level and any hydraulic fluid leaks prior to any extensive electrical diagnostics; refer to Liftgate Hydraulic System Refilling (Liftgate Hydraulic System Refilling).

The liftgate module also receives input from 2 pressure sensing object detection sensors. If either of these sensors indicates an object may be pinched as the liftgate is brought to the closed position, the liftgate will reverse direction and power close operation will be suspended until the pressure against the sensor is released.

Whenever the liftgate module loses power or is disconnected, the ignition must be cycled OFF then ON in order to reactivate the liftgate module.

Certain SIR DTCs will make the power liftgate inoperative. Correct any SIR concern first before performing any extensive power liftgate diagnostics.

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 Description and Operation)
Electrical Information Reference

* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Circuit Testing (Circuit Testing)
* Wiring Repairs (Wiring Repairs)
* Connector Repairs (Connector Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Doors unlocked, command the liftgate to OPEN by pressing the liftgate button on the remote keyless entry transmitter. The liftgate latch assembly should release the liftgate and the liftgate should perform the power OPEN function.

• If the liftgate is completely inoperative, refer to Liftgate Inoperative.

• If the liftgate latch will release but the liftgate will not power OPEN, refer to Liftgate Power Open Inoperative.

2. Command the liftgate to CLOSE by pressing the liftgate button on the remote keyless entry transmitter. The liftgate should perform the power CLOSE function.

• If there is no movement of the liftgate during the power CLOSE command, refer to Liftgate Power Close Inoperative.

3. Observe the scan tool LGM Front Control Switch parameter while pressing the open/close switch on the S58B Rear Compartment Lid Unlatch Switch - Interior. The parameter should change between Inactive and Active.

• If the values do not change, refer to Interior Liftgate Control Switch Inoperative.

4. Observe the scan tool Liftgate Handle Sw parameter while pressing and releasing the S46 liftgate handle switch. The parameter should change between Active and Inactive

• If the values do not change, refer to Liftgate Handle Switch Inoperative.

5. With the liftgate open, observe the scan tool LGM Rear Close Switch parameter while pressing and releasing the B70 liftgate close switch. The parameter should change from Inactive to Active.

• If the value does not change, refer to Liftgate Close Switch Inoperative.

Circuit/System Testing

Liftgate Inoperative
1. Ignition OFF, disconnect the X2 harness connector at the K39 liftgate module.
2. Test for less than 1 ohm between the ground circuit terminal 6 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal listed below and ground:

* B+ circuit terminal 3
* B+ circuit terminal 4

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, replace the K39 liftgate module.

4. Test for less than 5 ohm between the control circuit terminal 1 and the control circuit terminal 2.

• If greater than the specified range, test either control circuit for a short to voltage or an open/high resistance. If the circuits test normal, test or replace the M31 liftgate latch assembly.

5. Test for infinite resistance between the control circuit terminal listed below and ground:

* Control circuit terminal 1
* Control circuit terminal 2

• If less than the specified value, test the control circuit for a short to ground. If circuit tests normal, test or replace the M31 liftgate latch assembly.

6. Ignition OFF, connect the X1 harness connector at the K39 liftgate module and disconnect the harness connector at the M31 liftgate latch assembly.
7. Test for less than 10 ohm between the low reference circuit terminal 2 and ground.

• If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K39 liftgate module.

8. Ignition ON, verify the scan tool Liftgate Latch Pawl Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the K39 liftgate module.

9. Install a 3 A fused jumper wire between the signal circuit terminal 5 and low reference circuit terminal 2. Verify the scan tool Liftgate Latch Pawl 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 K39 liftgate module.

10. Verify the scan tool Liftgate Latch Ratchet Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 6 for a short to ground. If the circuit tests normal, replace the K39 liftgate module.

11. Install a 3 A fused jumper wire between the signal circuit terminal 6 and low reference circuit terminal 2. Verify the scan tool Liftgate Latch Ratchet 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 K39 liftgate module.

12. Verify the scan tool Liftgate Latch Sector Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K39 liftgate module.

13. Install a 3 A fused jumper wire between the signal circuit terminal 4 and low reference circuit terminal 2. Verify the scan tool Liftgate Latch Sector 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 K39 liftgate module.

14. If all circuits test normal, test or replace the M31 liftgate latch assembly.

Liftgate Power Open Inoperative
1. Ignition OFF, disconnect the harness connector at the M17 liftgate motor assembly.
2. Test for less than 25 ohm between the control circuit terminal A and ground.

• If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K39 liftgate module.

3. Test for less than 25 ohm between the control circuit terminal B and ground.

• If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K39 liftgate module.

Note: Verify that the interior liftgate control switch mode selector is in the 3/4 or the Max position

4. Connect a test lamp between the control circuit terminal A and control circuit terminal B.
5. Ignition ON, with the liftgate in the open position, command the liftgate to CLOSE by pressing the B70 liftgate close switch. The test lamp should illuminate during the CLOSE command.

• If the test lamp does not illuminate, test control circuit terminal A for a short to ground. If the circuit tests normal, replace the K39 liftgate module.

6. With the liftgate in the closed position, command the liftgate to OPEN by pressing the S46 liftgate handle switch. The test lamp should illuminate during the OPEN command.

• If the test lamp does not illuminate, test control circuit terminal B for a short to ground. If the circuit tests normal, replace the K39 liftgate module.

7. If all circuits test normal, test or replace the M17 liftgate motor assembly.

Liftgate Power Close Inoperative
1. Ignition OFF, disconnect the harness connector at the B71L liftgate object sensor - left.
2. Test for less than 10 ohm between the low reference circuit terminal A and ground.

• If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K39 liftgate module.

3. Disconnect the harness connector at the B71R liftgate object sensor - right.
4. Ignition ON, test for 4.75-5.25 V between the signal circuit terminal B and ground.

• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K39 liftgate module.
• If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K39 liftgate module.

5. Test of infinite resistance between the signal circuit terminal A and ground.

• If not the specified value, test the signal circuit for a short to ground.

6. Test for less than 10 ohm between the signal circuit terminal A at the B71R liftgate object sensor - right and the signal circuit terminal B at the B71L liftgate object sensor - left.

• If greater than the specified range, test the signal circuit for an open/high resistance.

7. If all circuits test normal, test or replace the appropriate B71 liftgate object sensor.

Interior Liftgate Control Switch Inoperative
1. Ignition OFF, disconnect the harness connector at the S58B rear compartment lid unlatch switch - interior.
2. Test for less than 5 ohm between the low reference circuit terminal 1 and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K15D door control module - driver.

3. Ignition ON, verify the scan tool LGM Front Control Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K15D door control module - driver.

4. Install a 3A fused jumper wire between the signal circuit terminal 4 and ground. Verify the scan tool LGM 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 K15D door control module - driver.

5. If all circuits test normal, test or replace the S58B rear compartment lid unlatch switch - interior.

Liftgate Handle Switch Inoperative
1. Ignition OFF, disconnect the X903 inline connector.
2. Test for less than 10 ohm between the low reference circuit terminal 2 and ground.

• If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance.

3. Ignition ON, verify the scan tool Liftgate Handle Sw. parameter is Inactive.

• If not the specified value, test the signal circuit terminal 7 for a short to ground. If the circuit tests normal, replace the K39 liftgate module.

4. Connect a 3 A fused jumper wire between the signal circuit terminal 7 and ground, verify the scan tool Liftgate Handle Sw. 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 K39 liftgate module.

5. If all circuits test normal, test or replace the S46 liftgate handle switch.

Liftgate Close Switch Inoperative
1. Ignition OFF, disconnect the harness connector at the B70 liftgate close switch.
2. Test for less than 10 ohm between the low reference circuit terminal 3 and ground.

• If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance.

3. Ignition ON, verify the scan tool LGM Rear Close Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K39 liftgate module

4. Connect a 3 A fused jumper wire between the signal circuit terminal 4 and ground, verify the scan tool LGM Rear Close 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 K39 liftgate module.

5. If all circuits test normal, test or replace the B70 liftgate close switch.

Component Testing

Liftgate Object Sensor
1. Ignition OFF, disconnect the harness connector at the B71R liftgate object sensor - right.
2. Test for 10k ohm between the signal terminal A and the low reference terminal B.

• If not within the specified range, replace the B71R liftgate object sensor - right.

3. Disconnect the harness connector at the B71L liftgate object sensor - left.
4. Test for 10k ohm between the signal terminal A and the low reference terminal B.

• If resistance is not within the specified range, replace the B71L liftgate object sensor - left.

Liftgate Handle Switch
1. Ignition OFF, disconnect the X903 inline connector.
2. Test for infinite resistance between the signal terminal 7 and the low reference terminal 2 with the switch in the open position.

• If not the specified value, replace the S46 liftgate handle switch.

3. Test for less than 2 ohm between the signal terminal 7 and the low reference terminal 2 with the switch in the closed position.

• If greater than the specified range, replace the S46 liftgate handle switch.

Liftgate Latch Assembly
1. Ignition OFF, disconnect the harness connector at the M31 liftgate latch assembly.
2. Install a 20 A fused jumper wire between one of the control terminals and 12V. Momentarily install a jumper wire between the other control terminal and ground. Reverse the jumper wires at least two times, the M31 liftgate latch assembly should perform the CINCH and RELEASE functions.

• If it does not perform as specified, replace the M31 liftgate latch assembly.

Interior Liftgate Control Switch
1. Ignition OFF, disconnect the harness connector at the S58B rear compartment lid unlatch switch - interior.
2. Test for infinite resistance between the signal terminal 4 and the low reference terminal 1 with the liftgate open switch in the inactive position.

• If not the specified value, replace the S58B rear compartment lid unlatch switch - interior.

3. Test for less than 3 ohm between the signal terminal 4 and the low reference terminal 1 with the liftgate open switch in the active position.

• If greater than the specified range, replace the S58B rear compartment lid unlatch switch - interior.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Liftgate Outside Handle Replacement (Service and Repair)
* Liftgate Latch Replacement (Liftgate Latch Replacement)
* Liftgate Hydraulic Pump Motor Replacement (Liftgate Hydraulic Pump Motor Replacement)
* Rear Compartment Lid Release Switch Replacement (Sedan) (Service and Repair)
* Liftgate Side Upper Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for Driver Door Lock/Window Switch and liftgate module replacement, setup and programming

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