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Home >> Chevrolet >> 2018 >> Suburban 3500 HD LT >> Repair and Diagnosis >> External Pages >> Different car >> Section 9 (Engine Controls And Fuel - 5.3L (L83) Or 6.2L (L86) - DTC P0443 To DTC P3452 And Diagnostic Information And Procedures) >> Diagnostic Information And Procedures >> DTC P0685, P0686, P0687, P0689, P0690 Or P1682: Engine Controls Ignition Relay Control Circuit >> Circuit/System Testing

Circuit/System Testing

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2018 GMC Yukon XL, 2018 GMC Yukon, 2018 Chevrolet Tahoe, 2018 Chevrolet Suburban, and 2018 Cadillac Escalade ESV. However, it is still accessible from the selected car via links, so may be relevant.
  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 30 & Ground
    • B+ circuit terminal 86 & 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 85 & B+ circuit terminal 86
  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 85 @ Relay Socket & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V
    5. Ignition/Vehicle - Off
    6. Test for less than 2 Ω between the test points:Control circuit terminal 85 @ Relay Socket & The other end of the circuit @ Control module harness
      • If 2 Ω or greater - Repair the open/high resistance in the circuit.
      • If less than 2 Ω - 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 85 @ 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: F51UA 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 Ω between the test points:Ignition circuit terminal 87 @ Relay Socket & Ignition circuit terminal 73 @ Control module harness
      • If 2 Ω or greater - Repair the open/high resistance in the circuit.
      • If less than 2 Ω - 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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