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DanielJones
DanielJones, ASE Certified Technician
Category: GM
Satisfied Customers: 505
Experience:  GM A Tech at Straub Buick GMC
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Left turn signal not working. Replaced the signal switch and

Customer Question

Left turn signal not working. Replaced the signal switch and nothing everything else works. Looked for bad fuses found nothing
Submitted: 1 year ago.
Category: GM
Expert:  DanielJones replied 1 year ago.

Hello. Welcome to the site. Thanks for coming. I'm ***** *****.
I'm here to provide as much information and insight as I can, to best answer your question.

Do the lights flash when you put the hazard switch on?

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Customer: replied 1 year ago.
Expert:  DanielJones replied 1 year ago.

All other lights work, brake lights, parking lights?

Both left side turn signals don't work when turn signal is turned on , but they work with the hazard switch?

Customer: replied 1 year ago.
sir all the lights work high, low, stops, emergency all work just fine except the left blinker
Expert:  DanielJones replied 1 year ago.

When the turn signal switch is placed in either the left or right position, a ground signal is completed from the turn signal switch to the Body Control Module(BCM).

The BCM then sends an ON-OFF voltage signal through the fuses to the appropriate turn signal lamps or to all of the turn signal fuses.

You will need to check the circuit from the turn signal switch to the BCM.

Customer: replied 1 year ago.
How do I do that
Expert:  DanielJones replied 1 year ago.

Do you have access to a scan tool that can access the BCM Data?

Customer: replied 1 year ago.
No sir
Expert:  DanielJones replied 1 year ago.

BCM is located In the passenger compartment, on the lower left side of the I/P, to the left of the steering column.

Turn Signal Lamps Malfunction

  1. Ignition OFF, disconnect the X4 harness connector at the BCM.
  2. Verify that a test lamp illuminates between the B+ circuit terminal 1 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 2 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 3 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, connect the X4 harness connector at the BCM.
  6. Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp.
  7. Ignition OFF, exterior lamps OFF, test for less than 5 Ω between the ground circuit terminal listed below and ground:
    • Park/Turn Signal Lamp – Terminal G
    • Tail/Stop and Turn Signal Lamp – Terminal GRD
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect a test lamp between the control circuit terminal listed below and ground:
    • Park/Turn Signal Lamp – Terminal MIN
    • Tail/Stop and Turn Signal Lamp – Terminal MJR
  9. Command the appropriate turn signal lamp 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.
  10. If all circuits test normal, replace the turn signal lamp.
Expert:  DanielJones replied 1 year ago.

BCM is item#3 in picture.

X4 connector is black.

Expert:  DanielJones replied 1 year ago.

Circuit/System Description

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM then applies a pulsating voltage to the front and rear turn signal lamps through their respective control circuits.

Expert:  DanielJones replied 1 year ago.

Hi, Just wanted to get an update on how you made out with vehicle.
Thanks
Dan

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