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Home >> GMC >> 2021 >> Terrain SL >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Vehicle Access System >> Diagnostic Information and Procedures >> Power Liftgate Malfunction >> Circuit/System Testing

Circuit/System Testing

Test 1

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S45B Liftgate Control Switch-Interior. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 1 and ground.
    • If 10 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Ignition ON.
  4. Verify the scan tool Liftgate Front Control Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 4 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 1.
  6. Verify the scan tool Liftgate Front Control Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Active 
  7. Test or replace the S45B Liftgate Control Switch-Interior.

Test 2

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S45B Liftgate Control Switch-Interior, ignition ON.
  2. Verify the scan tool Liftgate Mode Switch parameter is greater than 300 counts.
    • If 300 counts or less 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 3 and ground
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance, replace the K39 Liftgate Control Module
    • Go to next step: If greater than 300 counts 
  3. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 1.
  4. Verify the scan tool Liftgate Mode Switch parameter is less than 5 counts.
    • If 5 counts or greater 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • Go to next step: If less than 2 Ω, replace the K39 Liftgate Control Module
    • Go to next step: If less than 5 counts 
  5. Test or replace the S45B Liftgate Control Switch-Interior.

Test 3

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S46B Liftgate Unlatch Switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 30 Ω between the low reference circuit terminal 2 and ground.
    • If 30 Ω or greater 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module
    2. Test for less than 2 Ω in the low reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the low reference connection.
    • Go to next step: If less than 30 Ω 
  3. Ignition ON.
  4. Verify the scan tool Liftgate Handle Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 2 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2.
  6. Verify the scan tool Liftgate Handle Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, remove the 3 A fused jumper wire, disconnect the harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Active 
  7. Test or replace the S46B Liftgate Unlatch Switch.

Test 4

  1. Ignition OFF and all vehicle systems OFF, disconnect the X2 harness connector at the K39 Liftgate Control Module. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 6 and ground.
    • If 10 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF and all vehicle systems OFF, connect the X2 harness connector at the K39 Liftgate Control Module. Disconnect the harness connector at the A23C Liftgate Latch Assembly. It may take up to 2 minutes for all vehicle systems to power down.
  6. Test for less than 10 Ω between the low reference circuit terminal 6 and ground.
    • If 10 Ω or greater 
    1. Disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for less than 2 Ω in the low reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If less than 10 Ω 
  7. Ignition ON.
  8. Verify the scan tool Liftgate Latch Pawl Switch parameter is Closed.
    • If not Closed 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 1 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Closed 
  9. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 6.
  10. Verify the scan tool Liftgate Latch Pawl Switch parameter is Open
    • If not Open 
    1. Ignition OFF, remove the 3 A fused jumper wire, disconnect the harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Open 
  11. Verify the scan tool Liftgate Latch Ratchet Switch parameter is Closed.
    • If not Closed 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 5 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Closed 
  12. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the low reference circuit terminal 6.
  13. Verify the scan tool Liftgate Latch Ratchet Switch parameter is Open
    • If not Open 
    1. Ignition OFF, remove the 3 A fused jumper wire, disconnect the harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Open 
  14. Verify the scan tool Liftgate Latch Sector Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 2 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Inactive 
  15. Install a 3 A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 6.
  16. Verify the scan tool Liftgate Latch Sector Switch parameter is Active
    • If not Active 
    1. Ignition OFF, remove the 3 A fused jumper wire, disconnect the harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Active 
  17. Verify the scan tool Body Control Module Rear Closure Ajar Switch parameter is Inactive
    • If not Inactive 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 3 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Inactive 
  18. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the low reference circuit terminal 6.
  19. Verify the scan tool Body Control Module Rear Closure Ajar Switch parameter is Active
    • If not Active 
    1. Ignition OFF, remove the 3 A fused jumper wire, disconnect the harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Active 
  20. Test or replace the A23C Liftgate Latch Assembly.

Test 5

  1. Ignition OFF and all vehicle systems OFF. Disconnect the harness connector at the B70 Liftgate Close Switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 30 Ω between the low reference circuit terminal 3 and ground.
    • If 30 Ω or greater 
    1. Disconnect the harness connector at the K39 Liftgate Control Module
    2. Test for less than 2 Ω in the low reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the low reference connection.
    • Go to next step: If less than 30 Ω 
  3. Ignition ON
  4. Verify the scan tool Liftgate Rear Close Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the signal circuit terminal 4 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K39 Liftgate Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the low reference circuit terminal 3.
  6. Verify the scan tool Liftgate Rear Close Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module. Ignition ON
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • Go to next step: If Active 
  7. Test or replace the B70 Liftgate Close Switch.

Test 6

  1. Ignition OFF, disconnect the harness connector at the B71R Liftgate Object Sensor - Right. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 30 Ω between the low reference circuit terminal 2 and ground.
    • If 30 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the low reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
    • Go to next step: If less than 30 Ω 
  3. Disconnect the harness connector at the B71L Liftgate Object Sensor - Left.
  4. Ignition ON, test for 4.8 - 5.2 V between the 5 V reference circuit terminal 1 and ground.
    • If less than 4.8 V 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between the 5 V reference circuit and ground
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the 5 V reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • If greater than 5.2 V 
    1. Ignition OFF, disconnect the harness connector at the K39 Liftgate Control Module, Ignition ON.
    2. Test for less than 1 V between the 5 V reference circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K39 Liftgate Control Module.
    • Go to next step: If between 4.8 - 5.2 V 
  5. Test or replace the B71 Liftgate Object Sensors.

Test 7

  1. Ignition OFF, disconnect the X2 harness connector at the K39 Liftgate Control Module, Ignition ON
  2. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Disconnect the X3 harness connector.
    4. Test for infinite resistance between each control circuit listed below and ground:
      • Control circuit terminal 1 X3
      • Control circuit terminal 2 X3
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the M31 Liftgate Motor.
    • Go to next step: If the test lamp illuminates 
  3. Ignition OFF, connect the X2 harness connector at the K39 Liftgate Control Module and disconnect the harness connector at the M17 Liftgate Motor Assembly.
  4. Connect a test lamp between the control circuit terminal 1 and control circuit terminal 5, ignition ON.
  5. Liftgate closed and latched, verify the test lamp turns ON and OFF when pressing the S46 Liftgate Handle Switch.
    • If the test lamp remains OFF 
    6. NOTE:

    The liftgate must be opened and allowed to cinch closed each time this test is performed, repeating this test without opening and closing the liftgate will result in a misdiagnosis and replacement of a functional K39 Liftgate Control Module

  6. Open and completely close the liftgate, verify the test lamp turns ON and OFF when pressing the S46 Liftgate Handle Switch.
    • If the test lamp remains OFF 
    1. Ignition OFF, remove the test lamp, disconnect the X3 harness connector at the K39 Liftgate Control Module.
    2. Test for infinite resistance between each control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the control circuits end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K39 Liftgate Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, remove the test lamp, disconnect the X3 harness connector at the K39 Liftgate Control Module, ignition ON.
    2. Test for less than 1 V between each control circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K39 Liftgate Control Module
    • Go to next step: If the test lamp turns ON and Off 
  7. Replace the M17 Liftgate Motor Assembly.

Test 8

  1. Ignition OFF, disconnect the X3 harness connector at the K39 Liftgate Control Module.
  2. Test for infinite resistance between each circuit terminal listed below and ground:
    • Voltage reference circuit terminal 8 X3
    • Signal circuit terminal 9 X3
    • Signal circuit terminal 10 X3
    • Low reference circuit terminal 11 X3
    • If less than infinite resistance 
    • Replace the M17 Liftgate Motor Assembly
    • Go to next step: If infinite resistance 
  3. Ignition ON
  4. Test for less than 1 V between each circuit terminal listed below and ground:
    • Voltage reference circuit terminal 8 X3
    • Signal circuit terminal 9 X3
    • Signal circuit terminal 10 X3
    • Low reference circuit terminal 11 X3
    • If 1 V or greater 
    • Replace the M17 Liftgate Motor Assembly
    • Go to next step: If less than 1 V 
  5. Connect a 3A fused jumper wire between the voltage reference circuit terminal 8 and B+.
  6. Connect a 3A fused jumper wire between the low reference circuit terminal 11 and ground.
  7. Connect a DMM between the signal circuit terminal 9 and ground.
  8. Verify the voltage varies while manually opening and closing the liftgate.
    • If the voltage does not vary 
    • Replace the M17 Liftgate Motor Assembly
    • Go to next step: If the voltage varies 
  9. Connect a DMM between the signal circuit terminal 10 and ground.
  10. Verify the voltage varies while manually opening and closing the liftgate.
    • If the voltage does not vary 
    • Replace the M17 Liftgate Motor Assembly
    • Go to next step: If the voltage varies 
  11. Replace the K39 Liftgate Control Module
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