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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 2 (Engine Heating And Cooling System) >> Diagnostic Information and Procedures >> Cooling Fan Inoperative >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the Q85 Cooling Fan Clutch harness connector.
  2. Ignition ON, verify that a test lamp illuminates between ground circuit terminal A and B+.
    • If the test lamp does not illuminate 
    1. Ignition OFF, 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.
  3. Verify that a test lamp illuminates between the B+ circuit terminal B and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, and all vehicle systems OFF, it may take up to 2 minutes for all vehicle systems to power down.
    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, and all vehicle systems OFF, it may take up to 2 minutes for all vehicle systems to power down.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance, replace the Q85 Cooling Fan Clutch.
    • Go to next step: If the test lamp illuminates 
  4. Connect a DMM, set on the diode setting, between the control circuit terminal 85 and ground at the KR20F Cooling Fan Relay.
  5. Verify the DMM reading is greater than 2.5 V or displays O.L. with the cooling fan commanded OFF.
    • If 2.5 V or less 
    1. Ignition OFF, and all vehicle systems OFF, it may take up to 2 minutes for all vehicle systems to power down.
    2. Disconnect the harness connector X1 at the K20 Engine Control Module.
    3. Test for infinite resistance between the KR20F Cooling Fan Relay control circuit terminal 85 and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance, replace the K20 Engine Control Module.
    • Go to next step: If greater than 2.5 V or displays O.L. 
  6. Activate the cooling fan ON by turning on the A/C.
  7. Verify the DMM reading is less than 1 V.
    • If 1 V or greater 
    1. Ignition OFF.
    2. Disconnect the harness connector X1 at the K20 Engine Control Module, ignition ON.
    3. Test for less than 1 V between the KR20F Cooling Fan Relay control circuit terminal 85 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
    • Go to next step: If less than 1 V 
  8. Replace the K20 Engine Control Module.
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