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Home >> Cadillac >> 2017 >> CTS Base, AWD >> Repair and Diagnosis >> Accessories & Equipment >> Drivers Assistance Systems - ADAS >> Object Detection System And Pedestrian Protection System >> Diagnostic Information and Procedures >> DTC B127B: Rearview Camera Input Signal Circuit Missing Reference >> Circuit/System Testing
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Circuit/System Testing

    NOTE:

    If the condition is intermittent or cannot be duplicated, disconnect the connectors and add Nyogel lubricant 760G. This procedure will correct the high resistance condition due to terminal fretting corrosion.

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the B87 Rearview Camera. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 5 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 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the ignition circuit terminal 6 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse. Refer to Power Mode Mismatch .
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the B87 Rearview Camera.
    • If the test lamp illuminates 
  5. Engine running, park brake applied, transmission in R.
  6. Verify a test lamp illuminates between the control circuit terminal 3 and ground.
    • If the test lamp does not illuminate 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is good and there is voltage at the fuse. Refer to Backup Lamps Malfunction .
    • If the test lamp illuminates 
  7. Ignition OFF, disconnect the X2 harness connector at the K74 Human Machine Interface Control Module, ignition ON.
  8. Test for less than 1 V between the signal circuit terminals listed below and ground:
    • K74 Human Machine Interface Control Module signal (+) circuit terminal 5 X2
    • K74 Human Machine Interface Control Module signal (-) circuit terminal 6 X2
    • If 1 V or greater 

      Repair the short to voltage on the circuit.

    • If less than 1 V 
  9. Test for infinite resistance between the signal circuit terminals listed below and ground:
    • K74 Human Machine Interface Control Module signal (+) circuit terminal 5 X2
    • K74 Human Machine Interface Control Module signal (-) circuit terminal 6 X2
    • If less than infinite resistance 

      Repair the short to ground on the circuit.

    • If infinite resistance 
  10. Test for less than 2 Ω between the K74 Human Machine Interface Control Module signal (+) circuit terminal 5 X2 and the B87 Rearview Camera signal (+) circuit terminal 1.
    • If 2 Ω or greater 

      Repair the open/high resistance on the circuit.

    • If less than 2 Ω 
  11. Test for less than 2 Ω between the K74 Human Machine Interface Control Module signal (-) circuit terminal 6 X2 and the B87 Rearview Camera signal (-) circuit terminal 4.
    • If 2 Ω or greater 

      Repair the open/high resistance on the circuit.

    • If less than 2 Ω 
  12. Replace the B87 Rearview Camera.
  13. Engine running, transmission in R,
  14. Verify a clear rear vision image is displayed on the P17 Info Display Module.
    • If a clear rear vision image is not displayed 

      Replace the K74 Human Machine Interface Control Module.

    • If a clear rear vision image is displayed 
  15. All OK.