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Home >> Cadillac >> 2021 >> XT5 Sport >> Repair and Diagnosis >> External Pages >> Different car >> Section 838 (Automatic Transmission - 10L1000 (MGM MGU) - Diagnostic Information And Procedures (1 Of 2)) >> Diagnostic Information and Procedures >> DTC P0658 or P0659 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2023 GMC Sierra 3500 HD and 2023 GMC Sierra 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition/Vehicle - Off
  2. Disconnect the electrical connector: X1@T12 Automatic Transmission Assembly
  3. Connect a test lamp between the test points: Control circuit terminal 11 (harness side) & Ground
  4. Ignition - On/Vehicle - In Service Mode
    5. NOTE:

    The test lamp may not turn Off completely when the control function is commanded Off as the control module continues to supply a small amount of current on the circuit.

  5. Perform the scan tool control function: High Side Driver 1 - 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 electrical connector: K71 Transmission Control Module
    3. Test for infinite resistance between the test points: Control circuit terminal 11@Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    4. Test for less than 2 ohms between the test points: Control circuit terminal 11@Component harness & Terminal 33@ Control module harness
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component: K71 Transmission Control Module
    • If the test lamp is always On 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector: K71 Transmission Control Module
    3. Ignition - On/Vehicle - In Service Mode
    4. Test for less than 1 V between the test points: Control circuit terminal 11@Component harness & Terminal 33@ Control module harness
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V - Replace the component: K71 Transmission Control Module
    • Go to next step: If the test lamp turns On and Off 
  6. Ignition/Vehicle - Off & Remove - Test lamp
  7. Connect the electrical connector: X1@T12 Automatic Transmission Assembly
  8. Remove the component: Automatic Transmission Fluid Pan
  9. Disconnect the electrical connector: X177
  10. Connect a test lamp between the test points: Control circuit terminal 4 (harness side) & Ground
  11. Ignition - On/Vehicle - In Service Mode
  12. Perform the scan tool control function: High Side Driver 1 - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp does not turn On and Off 

      Replace the component: Automatic Transmission Wiring Harness - Pass-Thru

    • Go to next step: If the test lamp turns On and Off 
  13. Ignition/Vehicle - Off & Remove - Test lamp
  14. Connect the electrical connector: X177
  15. Disconnect the electrical connector:
    • Q77G Transmission Control Solenoid Valve 7
    • Q77H Transmission Control Solenoid Valve 8
  16. Connect a test lamp between the test points: Control circuit terminal 1 (harness side) @Q77G Transmission Control Solenoid Valve 7 & Ground
  17. Perform the scan tool control function: High Side Driver 1 - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp does not turn On and Off 

      Replace the component: Automatic Transmission Wiring Harness - Main/Solenoid

    • Go to next step: If the test lamp turns On and Off 
  18. Test or replace the component:
    • Q77G Transmission Control Solenoid Valve 7
    • Q77H Transmission Control Solenoid Valve 8
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