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Home >> Isuzu >> 2007 >> i-290 LS, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 39 (Lighting Systems) >> 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 2007 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION: The high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns:
  • Never open the high intensity discharge system ballast or the arc tube assembly starter.
  • Never probe between the high intensity discharge system ballast output connector and the arc tube assembly.

Turn Signal/Multifunction Switch Circuit Test.

  1. Ignition OFF, disconnect the C3 harness connector at the turn signal/multifunction switch.
  2. Test for less than 5.0 ohms of resistance between the ground circuit terminal G and ground.
    • If greater than the specified range, 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 F 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 H for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3A fused jumper wire between the signal circuit terminal F and the ground circuit terminal G. 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 an open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3A fused jumper wire between the signal circuit terminal H and the ground circuit terminal G. 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 an 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 Circuit Test.

  1. Ignition OFF, disconnect the C4 harness connector at the BCM.
  2. Ignition ON, verify a test lamp illuminates between the following B+ terminals and ground.
    • B+ terminal 1
    • B+ terminal 3
    • B+ terminal 4
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit fuse is open, test the B+ circuit and the respective turn signal circuits for a short to ground.
  3. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
  4. Test for less than 5.0 ohms of resistance between the appropriate ground circuit terminal listed below and ground.
    • Headlamp Assembly terminal A (and T72)
    • Headlamp Assembly terminal H (T84)
    • Repeater Lamp terminal B -- Export
    • Tail Lamp Assembly terminal C -- Domestic
    • Tail Lamp Assembly terminal H -- Export
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Connect a test lamp between the appropriate supply voltage circuit terminal listed below and the ground.
    • Headlamp Assembly terminal C
    • Repeater Lamp terminal A -- Export
    • Tail Lamp Assembly terminal B -- Domestic
    • Tail Lamp Assembly terminal G -- Export
  6. Ignition ON, command the inoperative 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the appropriate turn signal bulb.

Outside Rearview Mirror Turn Signal Circuit Test

  1. Ignition OFF, disconnect the C1 harness connector at the inoperative outside rearview mirror.
  2. Connect a test lamp between the low reference circuit terminal 2 and B+.
  3. Ignition ON, command the appropriate LF or RF 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 low reference circuit for a short to ground. If the circuit tests normal, replace the door module.
    • If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Connect a test lamp between the supply voltage circuit terminal 1 and ground.
  5. Ignition ON, command the appropriate LF or RF 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 supply voltage circuit for a short to voltage.
    • If the test lamp is always OFF, test the supply voltage circuit for an open/high resistance.
  6. If all circuits test normal, test or replace the outside rearview mirror lamp bulb.

Tail Lamp Outage Detection Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate tail lamp assembly.
  2. Ignition ON, test for B+ between the signal circuit terminal D and ground.
    • If less than B+, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  3. Ignition ON, connect a test lamp between the signal circuit terminal D and ground. The test lamp should not Illuminate.
    • If the test lamp illuminates, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  4. If all circuits test normal, test or replace the tail lamp assembly.

Turn Signal Indicators Malfunction

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