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Home >> GMC >> 2018 >> Terrain SL >> Repair and Diagnosis >> Body & Frame >> Windows >> Fixed And MOVEABLE Window System >> Diagnostic Information And Procedures >> Rear Window Defogger Malfunction >> Circuit/System Testing

Circuit/System Testing

    NOTE:

    It may take up to 2 min for all vehicle systems to power down before an accurate ground or low reference circuit continuity test can be performed.

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Remove the component: KR5 Rear Defogger Relay
  3. Test for less than 10 Ω between the test points: Ground circuit terminal 2 & Ground
    • If 10 Ω or greater 
    1. Disconnect Ground Connection
    2. Test for less than 2 Ω between the test points: Ground circuit terminal 2 & Ground Connection
      • 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.
    • Go to next step: If less than 10 Ω 
  4. Connect a test lamp between the test points: Control circuit terminal 1 & Ground circuit terminal 2
  5. Ignition - On/Vehicle - In Service Mode
  6. Perform the scan tool control function: Rear Defogger - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp is always Off 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector: X2 K33 HVAC Control Module
    3. Test for infinite resistance between the test points: Control circuit terminal 1 @ Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance
    4. Test for less than 2 Ω between the test points: Control circuit terminal 1 @ Relay Socket & Terminal 19 X2 @ Control module harness
      • If 2 Ω or greater - Repair the open/high resistance in the circuit.
      • If less than 2 Ω - Replace the component: K33 HVAC Control Module
    • If the test lamp is always On 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector: K33 HVAC Control Module
    3. Ignition - On/Vehicle - In Service Mode
    4. Test for less than 1 V between the test points: Control circuit terminal 1 @ Relay Socket & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V - Replace the component: K33 HVAC Control Module
    • Go to next step: If the test lamp turns On and Off 
  7. Verify a test lamp turns On between the test points: B+ circuit terminal 3 & Ground
    • If the test lamp does not turn On and the circuit fuse is OK 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for less than 2 Ω between the test points: B+ circuit terminal 3 @ Relay Socket & Output terminal @ Fuse
      • 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.
    • If the test lamp does not turn On and the circuit fuse is open 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for infinite resistance between the test points: B+ circuit terminal 3 & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance
    3. Disconnect the electrical connector: X1 & X2 E18 Rear Defogger Grid
    4. Test for infinite resistance between the test points: Control circuit terminal 5 @ Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance
    5. Replace the component: Fuse
    6. Install the component: KR5 Rear Defogger Relay
    7. Connect a test lamp between the test points: Control circuit terminal 1 X1 & Ground circuit terminal 1 X2
    8. Ignition - On/Vehicle - In Service Mode
    9. Perform the scan tool control function: Rear Defogger - On and Off

      Verify the test lamp turns On and Off.

      • If the test lamp does not turn On and Off - Test or replace the component: KR5 Rear Defogger Relay
      • If the test lamp turns On and Off - Test or replace the component: E18 Rear Defogger Grid
    • Go to next step: If the test lamp turns On 
  8. Momentarily connect a 30 A fused jumper wire between the test points: B+ circuit terminal 3 & Control circuit terminal 5

    Verify the component does not turn On and Off when connecting and disconnecting the jumper wire: E18 Rear Defogger Grid

    • If the component turns On and Off 

      Test or replace the component: KR5 Rear Defogger Relay

    • Go to next step: If the component does not turn On and Off 
  9. Ignition/Vehicle & All vehicle systems - Off
  10. Install the component: KR5 Rear Defogger Relay
  11. Disconnect the electrical connector: X1 & X2 E18 Rear Defogger Grid
  12. Test for less than 10 Ω between the test points: Ground circuit terminal 1 X2 & Ground
    • If 10 Ω or greater 
    1. Disconnect Ground Connection
    2. Test for less than 2 Ω between the test points: Ground circuit terminal 1 X2 @ Component harness & Ground Connection
      • 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.
    • Go to next step: If less than 10 Ω 
  13. Connect a test lamp between the test points: Control circuit terminal 1 X1 & Ground circuit terminal 1 X2
  14. Ignition - On/Vehicle - In Service Mode
  15. Perform the scan tool control function: Rear Defogger - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp is always Off 

      Repair the open/high resistance in the circuit: Control circuit

    • If the test lamp is always On 

      Repair the short to voltage on the circuit: Control circuit

    • Go to next step: If the test lamp turns On and Off 
  16. Test or replace the component: E18 Rear Defogger Grid
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