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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 274 (Lighting System - DTC B3891 To DTC C0297 And Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> Turn Signal Lamps and/or Indicators Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the S78 Turn Signal/Multifunction Switch. It may take up to 2 min 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.
    • If less than 10 Ω 
  3. Ignition ON.
  4. Verify the scan tool Left Turn Signal Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X3 harness connector at the K9 Body 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 K9 Body Control Module.
    • If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and ground.
  6. Verify the scan tool Left Turn Signal Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X3 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 5 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • 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 K9 Body Control Module.
    • If Active 
  7. Verify the scan tool Right Turn Signal Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X3 harness connector at the K9 Body 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 K9 Body Control Module.
    • If Inactive 
  8. Install a 3 A fused jumper wire between the signal circuit terminal 4 and ground.
  9. Verify the scan tool Right Turn Signal Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X3 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 4 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • 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 K9 Body Control Module.
    • If Active 
  10. Test or replace the S78 Turn Signal/Multifunction Switch.

Turn Signal Lamps Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, disconnect the X3 harness connector at the X53A Fuse Block - Rear Body.
    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, disconnect the X3 harness connector at the X53A Fuse Block - Rear Body.
    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 K9 Body Control Module.
    • If the test lamp illuminates 
  3. 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, disconnect the X1 harness connector at the X53A Fuse Block - Rear Body.
    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, disconnect the X1 harness connector at the X53A Fuse Block - Rear Body.
    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 K9 Body Control Module.
    • If the test lamp illuminates 
  4. Ignition OFF, connect the X1 harness connector at the K9 Body Control Module.
  5. Disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
  6. 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, disconnect the X2 harness connector at the X50A Fuse Block - Underhood.
    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, disconnect the X2 harness connector at the X50A Fuse Block - Underhood.
    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 K9 Body Control Module.
    • If the test lamp illuminates 
  7. Verify a test lamp illuminates between the B+ circuit terminal 4 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, disconnect the X2 harness connector at the X50A Fuse Block - Underhood.
    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, disconnect the X2 harness connector at the X50A Fuse Block - Underhood.
    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 K9 Body Control Module.
    • If the test lamp illuminates 
  8. Ignition OFF, connect the X5 harness connector at the K9 Body Control Module.
  9. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate turn signal lamp. It may take up to 2 min for all vehicle systems to power down.
  10. Test for less than 15 Ω between the appropriate ground circuit terminal listed below and ground.
    • E4Y Turn Signal Repeater Lamp - Left terminal 1
    • E4LF Turn Signal Lamp - Left Front terminal G (with T4F)
    • E4LF Turn Signal Lamp - Left Front terminal G (TR6-T4F)
    • E4N Park/Turn Signal Lamp - Left terminal G (TUJ-T4F)
    • E4Z Turn Signal Repeater Lamp - Right terminal 1
    • E4RF Turn Signal Lamp - Right Front terminal G (with T4F)
    • E4RF Turn Signal Lamp - Right Front terminal G (TR6-T4F)
    • E4P Park/Turn Signal Lamp - Right terminal G (TUJ-T4F)
    • E42L Tail Lamp Assembly - Left terminal A
    • E42R Tail Lamp Assembly - Right terminal D (without TVN)
    • E42R Tail Lamp Assembly - Right terminal E (with TVN)
    • If 15 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.
    • If less than 15 Ω 
  11. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E4Y Turn Signal Repeater Lamp - Left terminal 2
    • E4LF Turn Signal Lamp - Left Front terminal A (with T4F)
    • E4LF Turn Signal Lamp - Left Front terminal A (TR6-T4F)
    • E4N Park/Turn Signal Lamp - Left terminal A (TUJ-T4F)
    • E4Z Turn Signal Repeater Lamp - Right terminal 2
    • E4RF Turn Signal Lamp - Right Front terminal A (with T4F)
    • E4RF Turn Signal Lamp - Right Front terminal A (TR6-T4F)
    • E4P Park/Turn Signal Lamp - Right terminal A (TUJ-T4F)
    • E42L Tail Lamp Assembly - Left terminal E (with TVN)
    • E42L Tail Lamp Assembly - Left terminal C (without TVN)
    • E42R Tail Lamp Assembly - Right terminal A (with TVN)
    • E42R Tail Lamp Assembly - Right terminal B (without TVN)
  12. Verify the test lamp turns ON and OFF when commanding the appropriate Turn Signal Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module.
      • X5 left turn signals
      • X4 right turn signals
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module, ignition ON.
      • X5 left turn signals
      • X4 right turn signals
    2. Test for less than 1 V between the control circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K9 Body Control Module.
    • If the test lamp turns ON and OFF 
  13. Test or replace the E4 Turn Signal Lamp.

Turn Signal Lamp Outage Detection Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate E42 Tail Lamp Assembly, ignition ON.
  2. Test for B+ between the appropriate signal circuit terminal listed below and ground.
    • E42L Tail Lamp Assembly - Left terminal D
    • E42R Tail Lamp Assembly - Right terminal B (with TVN)
    • E42R Tail Lamp Assembly - Right terminal A (without TVN)
    • If not B+ 
    1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module.
      • X6 left tail lamp assembly
      • X7 right tail lamp assembly
    2. Test for infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    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 K9 Body Control Module.
    • If B+ 
  3. Verify a test lamp does not illuminate between the appropriate signal circuit terminal listed below and ground.
    • E42L Tail Lamp Assembly - Left terminal D
    • E42R Tail Lamp Assembly - Right terminal B (with TVN)
    • E42R Tail Lamp Assembly - Right terminal A (without TVN)
    • If the test lamp illuminates 
    1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module, ignition ON.
      • X6 left tail lamp assembly
      • X7 right tail lamp assembly
    2. Test for less than 1 V between the signal circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K9 Body Control Module.
    • If the test lamp does not illuminate 
  4. Test or replace the E42 Tail Lamp Assembly.
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