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Home >> Chevrolet >> 2019 >> Suburban 3500 HD LS >> Repair and Diagnosis >> Accessories & Equipment >> Exterior Lights >> Lighting System - Diagnostic Information And Procedures (DTC B3950-C0297) >> Diagnostic Information and Procedures >> Trailer Lamps Malfunction (Without MBM/MBR) >> Circuit/System Testing

Circuit/System Testing

Trailer Backup Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF.
  2. Test for less than 5 Ω between the ground circuit terminal B at the X88 Trailer Connector and ground.
    • If 5 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 5 Ω 
  3. Connect a test lamp between the control circuit terminal A at the X88 Trailer Connector and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the Backup Lamps ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood.
    2. Test for infinite resistance between the 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 circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the X50A Fuse Block - Underhood.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood, ignition ON.
    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 X50A Fuse Block - Underhood.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Test or replace the X88 Trailer Connector.

Trailer Park Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF.
  2. Test for less than 5 Ω between the ground circuit terminal B at the X88 Trailer Connector and ground.
    • If 5 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 5 Ω 
  3. Connect a test lamp between the control circuit terminal F at the X88 Trailer Connector and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the Park Lamps ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood.
    2. Test for infinite resistance between the 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 circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the X50A Fuse Block - Underhood.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood, ignition ON.
    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 X50A Fuse Block - Underhood.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Test or replace the X88 Trailer Connector.

Trailer Stop/Turn Signal Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF.
  2. Test for less than 5 Ω between the ground circuit terminal B at the X88 Trailer Connector and ground.
    • If 5 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 5 Ω 
  3. Disconnect the X5 harness connector at the X50A Fuse Block - Underhood, ignition ON.
  4. Verify a test lamp does not illuminate between the appropriate control circuit terminal listed below and ground.
    • Terminal K5 - left stop/turn signal
    • Terminal K6 - right stop/turn signal
    • If the test lamp illuminates 
    1. Ignition ON.
    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 X88 Trailer Connector.
    • Go to next step: If the test lamp does not illuminate 
  5. Ignition OFF, connect a 3 A fused jumper between the appropriate control circuit terminal listed below and B+, ignition ON.
    • Terminal K5 - left stop/turn signal
    • Terminal K6 - right stop/turn signal
  6. Verify a test lamp illuminates between the appropriate control circuit terminal listed below at the X88 Trailer Connector and ground.
    • Terminal G - left stop/turn signal
    • Terminal D - right stop/turn signal
    • If the test lamp does not illuminate 
    1. Ignition OFF, remove the 3 A fused jumper wire.
    2. Test for infinite resistance between the control circuit terminal 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 circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the X88 Trailer Connector.
    • Go to next step: If the test lamp illuminates 
  7. Ignition OFF, connect the X5 harness connector at the X50A Fuse Block - Underhood.
  8. Disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
  9. Verify a test lamp illuminates between the appropriate control circuit terminal listed below and ground.
    • Terminal 8 - left stop/turn signal
    • Terminal 17 - right stop/turn signal
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the X4 harness connector at the X50A Fuse Block - Underhood.
    2. Test for infinite resistance between the 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 circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the X50A Fuse Block - Underhood.
    • Go to next step: If the test lamp illuminates 
  10. Connect a 3 A fused jumper between the appropriate control circuit terminal listed below and ground, ignition ON.
    • Terminal 8 - left stop/turn signal
    • Terminal 17 - right stop/turn signal
  11. Verify a test lamp illuminates between the appropriate control circuit terminal listed below at the X88 Trailer Connector and ground.
    • Terminal G - left stop/turn signal
    • Terminal D - right stop/turn signal
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the X4 harness connector at the X50A Fuse Block - Underhood, ignition ON.
    2. Test for less than 1 V between the appropriate control circuit terminal listed below and ground.
      • Terminal 8 - left stop/turn signal
      • Terminal 17 - right stop/turn signal
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the X50A Fuse Block - Underhood.
    • Go to next step: If the test lamp illuminates 
  12. Test or replace the K9 Body Control Module.
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