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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 21 (Engine Controls And Fuel - 4.3L (LV1) - Diagnostic Information And Procedures (2 Of 2)) >> Diagnostic Information and Procedures >> DTC P0685-P0687, P0689, P0690, or P1682 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
  1. Ignition/Vehicle - Off
  2. Remove the component : KR75 Engine Controls Ignition Relay
  3. Verify a test lamp turns On between the test points :
    • B+ circuit terminal 85 & Ground
    • B+ circuit terminal 30 & Ground
    • If the test lamp does not turn On 

      Replace the component : X50A Fuse Block - Underhood

    • Go to next step : If the test lamp turns On 
  4. Ignition - On / Vehicle - In Service Mode
  5. Connect a test lamp between the test points : Control circuit terminal 86 & B+ circuit terminal 85
  6. Perform the scan tool control function : Engine Controls Ignition Relay - 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 appropriate electrical connector : K20 Engine 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
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • Go to next step : If less than 1 V
    5. Ignition/Vehicle - Off
    6. Test for less than 2 ohms between the test points : Control circuit terminal 86 @ Relay Socket & The other end of the circuit @ Control module harness
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component : K20 Engine Control Module
    • If the test lamp is always On 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the appropriate electrical connector : K20 Engine Control Module
    3. Test for infinite resistance between the test points : Control circuit terminal 86 @ Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component : K20 Engine Control Module
    • Go to next step : If the test lamp turns On and Off 
  7. Verify the fuse is not open : F78UA Fuse
    • If the fuse is open 
    1. Ignition/Vehicle & All vehicle systems - Off
    2. Disconnect the appropriate electrical connector : K20 Engine Control Module
    3. Test for infinite resistance between the test points : Output terminal @ Fuse & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component : K20 Engine Control Module
    • Go to next step : If the fuse is not open 
  8. Ignition - On / Vehicle - In Service Mode
  9. Verify a test lamp does not turn On between the test points : Ignition circuit terminal 87 @ Relay Socket & Ground
    • Go to next step : If the test lamp turns On 
  10. Disconnect the appropriate electrical connector : K20 Engine Control Module
  11. Test for less than 1 V between the test points : Ignition circuit terminal 73 @ Control module harness & Ground
    • If 1 V or greater - Repair the short to voltage on the circuit.
    • Go to next step : If the test lamp does not turn On 
  12. Ignition/Vehicle - Off
  13. Connect a 30 A fused jumper wire between the test points : Ignition circuit terminal 87 & B+ circuit terminal 30
  14. Ignition - On / Vehicle - In Service Mode
  15. Verify the scan tool parameter : Engine Controls Ignition Relay Feedback Signal = Within 1 V of the battery voltage
    • If not within 1 V of the battery voltage 
    1. Ignition/Vehicle - Off & Remove - Jumper wire(s)
    2. Disconnect the appropriate electrical connector : K20 Engine Control Module
    3. Test for less than 2 ohms between the test points : Ignition circuit terminal 87 @ Relay Socket & Ignition circuit terminal 73 @ Control module harness
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component : K20 Engine Control Module
    • Go to next step : If within 1 V of the battery voltage 
  16. Test or replace the component : KR75 Engine Controls Ignition Relay
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