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Home >> Cadillac >> 2017 >> ATS Base, 4D Sedan, RWD, Automatic Trans >> Repair and Diagnosis >> External Pages >> Different car >> Section 174 (Cellular System, Entertainment System, And Navigation System - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC B128F: Video Display Mode Control Signal >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2016 Cadillac CT6. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF.
  2. Disconnect the X1 harness connector at the appropriate P22 Video Display.
  3. Test for less than 10 Ω between the ground circuit terminal 3 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. 
  4. Verify that a test lamp illuminates between the B+ circuit terminal 1 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, remove the test lamp.
    2. Test for less than 2 Ω in the B+ 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 not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF, remove the test lamp.
    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 infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the P22 Video Display
    • If the test lamp illuminates 
  5. Ignition ON, rear seat entertainment system ON.
  6. Test for 5 V or greater between the control circuit terminal 2 and ground.
    • If less than 5 V. 
    1. Ignition OFF, disconnect the X1 harness connector at the A33 Media Disc Player.
    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 A33 Media Disc Player.
    • If 5 V or greater. 
  7. Ignition OFF.
  8. Verify the LVDS cable is properly connected at the P22 Video Display, A33 Media Disc Player and all in-line connectors, and there is no damage to the cable or connections.
    • If connection problems or cable damage is noted. 

      Perform the appropriate repair or replacement to correct any issues.

    • If no connection problems or cable damage is noted. 
  9. Test or replace the appropriate P22 Video Display
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