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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 57 (Automatic Transmission - 8L90 (M5U) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P0658, P0659, P2718, P2720, P2721, P2727, P2729, P2730, P281B, P281D, or P281E >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition/Vehicle - Off
  2. Disconnect the electrical connector: X175 @ T12 Automatic Transmission Assembly
    3. NOTE:

    All testing for this procedure is performed on the control module K71 side of the circuit.

  3. Connect a test lamp between the test points: Control circuit terminal 18 & Ground
  4. Ignition - On / Vehicle - In Service Mode
  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 18 @ 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 18 @ Component harness & The other end of the circuit
      • 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 18 @ Component harness & Ground
      • 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. Verify DTC P0658, P0659 is not set.
    • If the DTC is set 

      Refer to step 9

    • Go to next step: If the DTC is not set 
  7. Connect a test lamp between the test points:
    • { P2718, P2720, P2721 }Control circuit terminal 13 & Control circuit terminal 18 @ Component harness
    • { P2727, P2729, P2730 }Control circuit terminal 14 & Control circuit terminal 18 @ Component harness
    • { P281B, P281D, P281E }Control circuit terminal 1 & Control circuit terminal 18 @ Component harness
  8. Perform the scan tool control function: Transmission Control Solenoid Valve 4, 5, 8 - 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. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points:
      • { P2718, P2720, P2721 }Control circuit terminal 13 @ Component harness & Ground
      • { P2727, P2729, P2730 }Control circuit terminal 14 @ Component harness & Ground
      • { P281B, P281D, P281E }Control circuit terminal 1 @ Component harness & 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:
      • { P2718, P2720, P2721 }Control circuit terminal 13 @ Component harness & The other end of the circuit
      • { P2727, P2729, P2730 }Control circuit terminal 14 @ Component harness & The other end of the circuit
      • { P281B, P281D, P281E }Control circuit terminal 1 @ Component harness & The other end of the circuit
      • 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. Test for infinite resistance between the test points:
      • { P2718, P2720, P2721 }Control circuit terminal 13 @ Component harness & Ground
      • { P2727, P2729, P2730 }Control circuit terminal 14 @ Component harness & Ground
      • { P281B, P281D, P281E }Control circuit terminal 1 @ Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component: K71 Transmission Control Module
    • Go to next step: If the test lamp turns On and Off 
  9. Connect the electrical connector: X175 @ T12 Automatic Transmission Assembly
  10. Remove the component: Transmission Fluid Pan
  11. Disconnect the electrical connector: X176
  12. Connect a test lamp between the test points:
    • { P2718, P2720, P2721 }Control circuit terminal 9 & Control circuit terminal 4 @ Component harness
    • { P2727, P2729, P2730 }Control circuit terminal 7 & Control circuit terminal 4 @ Component harness
    • { P281B, P281D, P281E }Control circuit terminal 1 & Control circuit terminal 4 @ Component harness
  13. Perform the scan tool control function: Transmission Control Solenoid Valve 4, 5, 8 - 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 
  14. Connect the electrical connector: X176
  15. Disconnect the appropriate electrical connector: Q77 Transmission Control Solenoid Valve
  16. Verify a test lamp turns On between the test points: Control circuit terminal 2 & Control circuit terminal 1 @
    • If the test lamp does not turn On and Off 

      Replace the component: Automatic Transmission Control Wiring Harness

    • Go to next step: If the test lamp turns On and Off 
  17. Replace the appropriate component: Q77 Transmission Control Solenoid Valve
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