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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 18 (Lighting System) >> Diagnostic Information and Procedures >> Turn Signal Lamps and/or Indicators Malfunction >> Circuit/System Testing

Circuit/System Testing

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Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the turn signal/multifunction switch.
  2. Verify that a test lamp illuminates between the ground circuit terminal F and B+.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Left Turn Signal Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Right Turn Signal Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the BCM.
  5. Connect a 3 A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool Left Turn Signal Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  6. Connect a 3 A fused jumper wire between the signal circuit terminal D and ground. Verify the scan tool Right Turn Signal Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Turn Signal Lamps Malfunction

  1. Ignition OFF, disconnect the X4 harness connect at the BCM.
  2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminals listed below and ground.
    • B+ terminal 1
    • B+ terminal 2
    • B+ terminal 3
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuits test normal and the circuit fuse is open, test the appropriate control circuit terminal(s) listed below for a short to ground.
    • Terminal 5 X4 for an open BCM 3 fuse
    • Terminal 1 X5 and terminal 4 X5 for an open BCM 5 fuse
    • Terminal 2 X5 for an open BCM 6 fuse
  3. Ignition OFF, reconnect the X4 harness connector at the BCM.
  4. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
  5. Test for less than 5.0 Ω between the appropriate ground circuit terminal listed below and ground.
    • Front Turn Signal terminal C
    • Outside Rearview Mirror terminal D
    • Rear Turn Signal terminal G
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the appropriate control circuit terminal listed below and ground.
    • Front Turn Signal terminal A
    • Outside Rearview Mirror terminal B
    • Rear Turn Signal terminal A
  7. Ignition ON, command the appropriate turn signal ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  8. If all circuits test normal, test or replace the turn signal bulb.
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