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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 >> Headlamp Leveling Malfunction (Manual) >> 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.
  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E13 Headlamp Assembly. 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.
    • If less than 15 Ω 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminal 9 and ground.
    • If the test lamp does not illuminate 
    1. Ignition OFF, disconnect the X1 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
    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 
  5. Ignition OFF, disconnect the harness connector at the S42 Headlamp Leveling Switch. It may take up to 2 min for all vehicle systems to power down.
  6. 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.
    • If less than 10 Ω 
  7. Ignition ON.
  8. Verify a test lamp illuminates between the B+ circuit terminal 6 and ground.
    • If the test lamp does not illuminate 
    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
    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 
  9. Ignition OFF, connect the harness connector at the S42 Headlamp Leveling Switch.
  10. Ignition ON, exterior lights OFF.
  11. Test the voltage between the control circuit terminal 10 at the E13 Headlamp Assembly harness connector and ground for each S42 Headlamp Leveling Switch position listed below.
    • Headlamp leveling switch position 0 - 10 V - 11 V
    • Headlamp leveling switch position 1 - 8.5 V - 9.9 V
    • Headlamp leveling switch position 2 - 8 V - 9 V
    • Headlamp leveling switch position 3 - 6 V - 7 V
    • If less than the specified voltage range for each headlamp leveling switch position 
    1. Ignition OFF, disconnect the harness connector at the S42 Headlamp Leveling Switch.
    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 S42 Headlamp Leveling Switch.
    • If greater than the specified voltage range for each headlamp leveling switch position 
    1. Ignition OFF, disconnect the harness connector at the S42 Headlamp Leveling Switch, 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 S42 Headlamp Leveling Switch.
    • If within the specified voltage range for each headlamp leveling switch position 
  12. Test or replace the M29 Headlamp Leveling Actuator.
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