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Home >> Chevrolet >> 2017 >> Silverado 1500 SSV, 4WD, Part Time T/Case Control, Gas >> 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 85 and ground.
    • If 10 Ω or greater 
    1. Ground Connection - Disconnect
    2. Test for less than 2 Ω between the test points:Ground circuit terminal 85 & 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.
    • If less than 10 Ω 
  4. Connect a test lamp between the test points: Control circuit terminal 86 & ground circuit terminal 85
  5. Ignition - On / Vehicle - In Service Mode
  6. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.

    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: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 86@Relay Socket & ground
      1. If 1 V or greater - Repair the short to voltage on the circuit.
      2. If less than 1 V - Replace the component:K33 HVAC Control Module
    • If the test lamp turns On and Off 
  7. Momentarily connect a 30 A fused jumper wire between the test points:B+ circuit terminal 30 & control circuit terminal 87

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

    • If the test lamp is always OFF 
    • Test or replace the component:KR5 Rear Defogger Relay
    • If the component does not turn On and Off 
  8. Ignition ON, connect a 30 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
  9. Install the component:KR5 Rear Defogger Relay
  10. Disconnect the electrical connector:E18 Rear Defogger Grid
  11. Connect a test lamp between the test points:Control circuit terminal 1 and ground
  12. Ignition - On / Vehicle - In Service Mode
  13. 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

    • If the test lamp turns On and Off 
  14. Test or replace the component:E18 Rear Defogger Grid
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