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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 129 (Lighting System - DTC B0655 To DTC B3890) >> Diagnostic Information and Procedures >> DTC B388D: Rear Multifunction Carrier Switch >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2016 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition ON, test for 4.8-5.2 V between the trailer connector position switch signal circuit (5992 GN/BU) at the W8 Blunt Cut Trailer Provision and ground.
    • If less than 4.8V 
    1. Ignition OFF, disconnect the X1 harness connector at the K68 Trailer Lighting Control Module.
    2. 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
    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 K68 Trailer Lighting Control Module.
    • If greater than 5.2 V 
    1. Ignition OFF, disconnect the X1 harness connector at the K68 Trailer Lighting Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K68 Trailer Lighting Control Module.
    • If between 4.8-5.2 V 
  2. Test or replace the W8 Blunt Cut Trailer Provision.
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