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Home >> GMC >> 2021 >> Acadia AT4 >> Repair and Diagnosis >> External Pages >> Different car >> Section 413 (Automatic Transmission - 9T60 (M3G) Or 9T65 (M3W) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P18A2 or P18A4 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2023 GMC Acadia. 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 28 & Ground
  4. Ignition - On/Vehicle - In Service Mode
  5. Perform the scan tool control function: High Side Driver 2 - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp is always Off 
    1. Connect the electrical connector: X1@T12 Automatic Transmission Assembly
    2. Ignition/Vehicle - Off & Remove - Test lamp
    3. Disconnect the electrical connector: X1@T12 Automatic Transmission Assembly
    4. Disconnect the electrical connector: K71 Transmission Control Module
    5. Test for infinite resistance between the test points: Control circuit terminal 28@Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    6. Test for less than 2 ohms between the test points: Control circuit terminal 28@Component harness & Terminal 49@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. Remove - Test Lamp
    2. Connect the electrical connector: X1@T12 Automatic Transmission Assembly
    3. Ignition/Vehicle - Off
    4. Disconnect the electrical connector: X1@T12 Automatic Transmission Assembly
    5. Disconnect the electrical connector: K71 Transmission Control Module
    6. Ignition - On/Vehicle - In Service Mode
    7. Test for less than 1 V between the test points: Control circuit terminal 28@Component harness & Ground
      • If 1 V or greater - Repair the short to ground 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. Remove - Test Lamp
  7. Connect the electrical connector: X1@T12 Automatic Transmission Assembly
  8. Ignition/Vehicle - Off
  9. Disconnect the electrical connector: X1@T12 Automatic Transmission Assembly
  10. Disconnect the electrical connector: K71 Transmission Control Module
  11. Test for less than 2 ohms between the test points: Control circuit terminal 10@Component harness & Control circuit terminal 22@Control module harness
    • If 2 ohms or greater 

      Repair the open/high resistance in the circuit.

    • Go to next step: If less than 2 ohms 
  12. Test for infinite resistance between the test points: Control circuit terminal 10@Component harness & Ground
    • If less than infinite resistance 

      Repair short to ground on the circuit.

    • Go to next step: If infinite resistance 
  13. Ignition - On/Vehicle - In Service Mode
  14. Test for less than 1 V between the test points: Control circuit terminal 10 & Ground
    • If 1 V or greater 

      Repair the short to voltage on the circuit.

    • Go to next step: If less than 1 V 
  15. Connect the electrical connector: X1@T12 Automatic Transmission Assembly
  16. Ignition/Vehicle - Off
  17. Connect the electrical connector: K71 Transmission Control Module
  18. Disconnect the electrical connector: X1@T12 Automatic Transmission Assembly
  19. Remove the component: Control Valve Body Cover
  20. Connect the electrical connector: X1@T12 Automatic Transmission Assembly
  21. Disconnect the electrical connector: M123 Transmission Park Valve Lock Solenoid Actuator
  22. Connect a test lamp between the test points: Control circuit terminal 1@Component harness & Ground
  23. Ignition - On/Vehicle - In Service Mode
  24. Perform the scan tool control function: High Side Driver 2 - 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

    • Go to next step: If the test lamp turns On and Off 
  25. Connect a test lamp between the test points: Control circuit terminal 1@Component harness & Control circuit terminal 2@Component harness
  26. Perform the scan tool control function: Transmission Park Valve Lock Solenoid Actuator - 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

    • Go to next step: If the test lamp turns On and Off 
  27. Test or replace the component: M123 Transmission Park Valve Lock Solenoid Actuator
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