Mike's Workshop Manuals: Service manuals for every vehicle
Home >> Chevrolet >> 2016 >> City Express LS >> 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

Rear Defogger Switch Malfunction

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the A26 HVAC Controls. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 12 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.
    • Go to next step: If less than 10 Ω 
  3. Ignition ON.
  4. Verify the scan tool Rear Defogger Switch parameter is Off.
    • If not Off 
    1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the A26 HVAC Controls signal circuit terminal 13 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Off 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 13 and the ground circuit terminal 12.
  6. Verify the scan tool Rear Defogger Switch parameter is On.
    • If not On 
    1. Ignition OFF, remove the jumper wire, disconnect the harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • Go to next step: If On 
  7. Test or replace the A26 HVAC Controls.

Rear Defogger Malfunction

  1. Ignition OFF, and all vehicle systems OFF. Disconnect the harness connector at the E18 Rear Defogger Grid. 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 2 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.
    • Go to next step: If less than 10 Ω 
  3. Connect a test lamp between the control circuit terminal 1 and ground, ignition ON.
  4. Verify the test lamp does not turn ON and OFF when commanding the Rear Defogger On and Off with a scan tool.
    • If the test lamp turns ON and OFF 

      Test or replace the E18 Rear Defogger Grid.

    • Go to next step: If the test lamp does not turn ON and OFF 
  5. Ignition OFF, connect the harness connector at the E18 Rear Defogger Grid. Disconnect the X8 harness connector at the X50A Fuse Block-Underhood, ignition ON.
  6. Verify the E18 Rear Defogger Grid is not activated.
    • If the E18 Rear Defogger Grid is activated 
    1. Ignition OFF, disconnect the harness connector at the E18 Rear Defogger Grid, ignition ON.
    2. Test for less than 1 V between the control circuit terminal 5 X8 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, test or replace the E18 Rear Defogger Grid.
    • Go to next step: If the E18 Rear Defogger Grid is not activated 
  7. Connect a 20 A fused jumper wire between the control circuit terminal 5 X8 and B+.
  8. Verify the E18 Rear Defogger Grid activates.
    • If the E18 Rear Defogger Grid does not activate 
    1. Ignition OFF, remove the jumper wire, disconnect the harness connector at the E18 Rear Defogger Grid.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than Infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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, test or replace the E18 Rear Defogger Grid.
    • Go to next step: If the E18 Rear Defogger Grid activates 
  9. Replace the X50A Fuse Block-Underhood.

Rear Window Defogger Indicator Malfunction

  1. Ignition OFF, disconnect the harness connector at the A26 HVAC Controls
  2. Ignition ON, connect a test lamp between the control circuit terminal 14 and the ground circuit terminal 12.
  3. Verify the test lamp turns ON and OFF when commanding the Rear Defogger On and Off with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, remove the test lamp, disconnect the harness connector at the X50A Fuse Block-Underhood.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 X50A Fuse Block-Underhood.
    • If the test lamp is always ON 
    1. Ignition OFF, remove the test lamp, disconnect the harness connector at the X50A Fuse Block-Underhood, ignition ON.
    2. Test for less than 1 V between the control circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the X50A Fuse Block-Underhood
    • Go to next step: If the test lamp turns ON and OFF 
  4. Test or replace the A26 HVAC Controls.
scientia non olet · About Mike's Workshop Manuals