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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 335 (Mirror System) >> Diagnostic Information and Procedures >> Power Mirror Malfunction (Without AAB) >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2017 GMC Acadia. However, it is still accessible from the selected car via links, so may be relevant.

Both Outside Mirrors Inoperative

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S79D Window Switch - Driver. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 24 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. Verify a test lamp illuminates between the B+ circuit terminal 23 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 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.
    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 each of the control circuit terminals listed below and ground:
      • Terminal 2 control circuit
      • Terminal 3 control circuit
      • Terminal 4 control circuit
      • Terminal 6 control circuit
      • Terminal 7 control circuit
      • Terminal 8 control circuit
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, test or replace the appropriate M77 Outside Rearview Mirror Motor.
    • If the test lamp illuminates 
  4. Test or replace the S79D Window Switch - Driver.

Single Outside Mirror Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate A9 Outside Rearview Mirror. Ignition ON.
  2. Connect a test lamp between the control circuit terminal 9 and the control circuit terminal 12.
  3. Verify the test lamp illuminates when commanding the UP and DOWN functions with the S79D Window Switch - Driver.
    • If the test lamp does not illuminate during either of the UP and DOWN commands 
    1. Ignition OFF, remove the test lamp, disconnect the harness connector at the S79D Window Switch - Driver.
    2. Test for infinite resistance between each 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 each control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace at the S79D Window Switch - Driver.
      • If the test lamp is always ON 
    4. Ignition OFF, remove the test lamp, disconnect the harness connector at the S79D Window Switch - Driver, ignition ON.
    5. Test for less than 1 V between each control circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the S79D Window Switch - Driver.
    • If the test lamp illuminates during UP and DOWN the commands 
  4. Connect a test lamp between the control circuit terminal 10 and the control circuit terminal 12.
  5. Verify the test lamp illuminates when commanding the LEFT and RIGHT functions with the S79D Window Switch - Driver.
    • If the test lamp does not illuminate during either of the LEFT and RIGHT commands 
    1. Ignition OFF, remove the test lamp, disconnect the harness connector at the S79D Window Switch - Driver.
    2. Test for infinite resistance between each 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 each control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace at the S79D Window Switch - Driver.
      • If the test lamp is always ON 
    4. Ignition OFF, remove the test lamp, disconnect the harness connector at the S79D Window Switch - Driver, ignition ON.
    5. Test for less than 1 V between each control circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the S79D Window Switch - Driver.
    • If the test lamp illuminates during the LEFT and RIGHT commands 
  6. Test or replace the M77 Outside Rearview Mirror Motor.
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