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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 >> Headlamps Malfunction (Chevrolet, GMC) >> Circuit/System Testing

Circuit/System Testing

Headlamp Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S30 Headlamp Switch. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 15 Ω between the ground circuit terminal 8 and ground.
    • 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.
    • Go to next step: If less than 15 Ω 
  3. Ignition ON.
  4. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body 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 K9 Body Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 3 and ground.
  6. Verify the scan tool Automatic Headlamps Disable Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 3 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 K9 Body Control Module.
    • Go to next step: If Active 
  7. Verify the scan tool Park Lamps Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 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.
    • Go to next step: If Inactive 
  8. Install a 3 A fused jumper wire between the signal circuit terminal 5 and ground.
  9. Verify the scan tool Park Lamps Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 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.
      • 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 K9 Body Control Module.
    • Go to next step: If Active 
  10. Verify the scan tool Headlamps On Switch parameter is Inactive.
    • If not Inactive 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body 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 K9 Body Control Module.
    • Go to next step: If Inactive 
  11. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground.
  12. Verify the scan tool Headlamps On Switch parameter is Active.
    • If not Active 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 1 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 K9 Body Control Module.
    • Go to next step: If Active 
  13. Test or replace the S30 Headlamp Switch.

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, open and close drivers door, disconnect the X1 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 15 Ω between the ground circuit terminal 13 and ground.
    • 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.
    • Go to next step: If less than 15 Ω 
  3. Ignition ON.
  4. Verify the scan tool High Beam Select 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 14 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 14 and ground.
  6. Verify the scan tool High Beam Select 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 14 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 K9 Body Control Module.
    • Go to next step: If Active 
  7. Verify the scan tool Headlamps Flash 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 10 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  8. Install a 3 A fused jumper wire between the signal circuit terminal 10 and ground.
  9. Verify the scan tool Headlamps Flash 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 10 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 K9 Body Control Module.
    • Go to next step: If Active 
  10. Test or replace the S78 Turn Signal/Multifunction Switch.

Headlamps Malfunction - Low Beam (without T4F)

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate component listed below. It may take up to 2 min for all vehicle systems to power down.
    • E4G Headlamp - Left Low Beam
    • E4H Headlamp - Right Low Beam
  2. Test for less than 10 Ω between the appropriate ground circuit terminal listed below and ground.
    • E4G Headlamp - Left Low Beam socket terminal
    • E4H Headlamp - Right Low Beam socket terminal
    • 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. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E4G Headlamp - Left Low Beam socket terminal
    • E4H Headlamp - Right Low Beam socket terminal
  4. Verify the test lamp turns ON and OFF when commanding the appropriate Low Beam/Daytime Running Lamp ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module.
    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 K9 Body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X4 harness connector at the K9 Body Control Module, 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 K9 Body Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Test or replace the E4 Headlamp - Low beam.

Headlamps Malfunction - Low Beam (with T4F)

  1. Ignition OFF, disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
    2. NOTE:

    The test lamp in the following step will illuminate at LOW intensity. This is normal circuit operation and does not indicate a circuit malfunction.

  2. Verify a test lamp illuminates between the control circuit terminal 13 and ground.
    • 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 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 X50A Fuse Block - Underhood.
    • If the test lamp illuminates 
  3. Ignition OFF, connect a 3 A fused jumper between the control circuit terminal 13 and ground.
  4. Remove the left low beam fuse (F122UA) at the X50A Fuse Block - Underhood, ignition ON.
  5. Verify a test lamp illuminates between the left low beam fuse (F122UA) B+ switch control terminal and ground.
    • 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 control circuit terminal 13 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 illuminates 
  6. Ignition OFF, connect the X5 harness connector at the K9 Body Control Module.
  7. Install the left low beam fuse (F122UA) at the X50A Fuse Block - Underhood.
  8. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate component listed below. It may take up to 2 min for all vehicle systems to power down.
    • E13LA Headlamp Assembly - Left
    • E13RA Headlamp Assembly - Right
  9. Test for less than 10 Ω between the appropriate ground circuit terminal listed below and ground.
    • E13LA Headlamp Assembly - Left terminal 1 and terminal 4
    • E13RA Headlamp Assembly - Right terminal 1 and terminal 4
    • 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 
  10. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E13LA Headlamp Assembly - Left terminal 2
    • E13RA Headlamp Assembly - Right terminal 2
  11. Verify the test lamp turns ON and OFF when commanding the Low Beam Headlamps ON and OFF with the S30 Headlamp Switch.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X1 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 K9 Body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X1 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 K9 Body Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  12. Ignition OFF, replace the T7 Headlamp Ballast.
  13. Ignition ON, verify the appropriate low beam headlamp illuminates when commanded ON with the S30 Headlamp Switch.
    • If the low beam headlamp does not illuminate 
    1. Replace the E4 Headlamp - Low Beam bulb.
    • Go to next step: If the low beam headlamp illuminates 
  14. All OK.

Headlamps Malfunction - High Beam

  1. Ignition OFF, disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
    2. NOTE:

    The test lamp in the following step will illuminate at LOW intensity. This is normal circuit operation and does not indicate a circuit malfunction.

  2. Verify a test lamp illuminates between the control circuit terminal 18 and ground.
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the X3 harness connector at the X50A Fuse Block - Underhood.
    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 X50A Fuse Block - Underhood.
    • If the test lamp illuminates 
  3. Ignition OFF, connect a 3 A fused jumper between the control circuit terminal 18 and ground.
  4. Remove the high beam fuse (F95UA) at the X50A Fuse Block - Underhood, ignition ON.
  5. Verify a test lamp illuminates between the high beam fuse (F95UA) B+ switch control terminal and ground.
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the X3 harness connector at the X50A Fuse Block - Underhood, ignition ON.
    2. Test for less than 1 V between the control circuit terminal 18 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 illuminates 
  6. Ignition OFF, connect the X5 harness connector at the K9 Body Control Module.
  7. Install the high beam fuse (F95UA) at the X50A Fuse Block - Underhood.
  8. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate component listed below. It may take up to 2 min for all vehicle systems to power down.
    • E4E Headlamp - Left High Beam
    • E4F Headlamp - Right High Beam
  9. Test for less than 10 Ω between the appropriate ground circuit terminal listed below and ground.
    • E4E Headlamp - Left High Beam socket terminal
    • E4F Headlamp - Right High Beam socket terminal
    • 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 
  10. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • E4E Headlamp - Left High Beam socket terminal
    • E4F Headlamp - Right High Beam socket terminal
  11. Verify the test lamp turns ON and OFF when commanding the High Beams ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X1 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 K9 Body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X1 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 K9 Body Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  12. Test or replace the E4 Headlamp - High Beam.

High Beam Indicator Malfunction

  1. Ignition ON.
  2. Verify the high beam indicator turns ON and OFF when commanding the Instrument Cluster All Indicators Test ON and OFF with a scan tool.
    • If the high beam indicator is always OFF or remains ON 

      Replace the P16 Instrument Cluster.

    • Go to next step: If the high beam indicator turns ON and OFF 
  3. Replace the K9 Body Control Module.

Ambient Light Sensor Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the B10B Ambient Light/Sunload Sensor. It may take up to 10 min for all vehicle systems to power down.
  2. Test for less than 5 Ω between the low reference circuit terminal 6 and ground.
    • If 5 Ω or greater 
    1. Ignition OFF, disconnect the X2 harness connector at the K33 HVAC 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 K33 HVAC Control Module.
    • Go to next step: If less than 5 Ω 
  3. Ignition ON.
  4. Verify the scan tool Ambient Light Sensor parameter is greater than 4.65 V.
    • If 4.65 V or less 
    1. Ignition OFF, disconnect the X2 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.
    • Go to next step: If greater than 4.65 V 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the low reference circuit terminal 6.
  6. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V.
    • If 0.196 V or greater 
    1. Ignition OFF, disconnect the X2 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.
      • 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 K9 Body Control Module.
    • Go to next step: If less than 0.196 V 
  7. Test or replace the B10B Ambient Light/Sunload Sensor.
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