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Home >> GMC >> 2021 >> Terrain SLE, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 91 (Automatic Transmission - 9T45 (M3U) Or 9T50 (M3D M3H) - 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 2020 GMC Terrain and 2020 Chevrolet Equinox. 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 Control Solenoid Valve 11 - 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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