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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 P0722, P0723, P077C, or P077D >> 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.
    NOTE:

    It may take up to 2 min for all vehicle systems to power down before an accurate ground or low reference circuit continuity test can be performed.

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Disconnect the electrical connector: X175 @ T12 Automatic Transmission Assembly
  3. Ignition - On / Vehicle - In Service Mode
  4. Test for 8. 5 to 9. 5 V between the test points: 9 V Reference circuit1Terminal 25 @ Component harness & Ground
    • If less than 8. 5 V 
    1. Ignition/Vehicle - Off
    2. Disconnect the electrical connector: X175 @ K71 Transmission Control Module
    3. Test for infinite resistance between the test points: 9 V Reference circuit1Terminal 25 @ 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: 9 V Reference circuit1Terminal 25 @ Component harness & Terminal 7 @ 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 greater than 9. 5 V 
    1. Ignition/Vehicle - Off
    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: 9 V Reference circuit1Terminal 25 @ 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 between 8. 5 and 9. 5 V 
  5. Ignition/Vehicle - Off
  6. Install the special tool: EL-38522 Variable Signal Generator
    • Red lead @ Signal circuit terminal 24
    • Black lead @ Ground
    • Set the voltage to 5 V
    • Set the frequency to 300 Hz
    • Set the duty cycle to 50%
  7. Ignition - On / Vehicle - In Service Mode
  8. Verify the scan tool parameter: Transmission OSS = 230 to 280 RPM
    • If not between 230 and 280 RPM 
    1. Ignition/Vehicle - Off
    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: Signal circuit terminal 24 @ 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 infinite resistance between the test points: Signal circuit terminal 24 @ Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    7. Test for less than 2 ohms between the test points: Signal circuit terminal 24 @ Component harness & Terminal 14 @ 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
    • Go to next step: If between 230 and 280 RPM 
  9. Ignition/Vehicle - Off
  10. Connect the electrical connector: X175 @ T12 Automatic Transmission Assembly
  11. Remove the component: Automatic Transmission Fluid Pan
  12. Disconnect the electrical connector: X177
  13. Ignition - On / Vehicle - In Service Mode
  14. Test for 8. 5 to 9. 5 V between the test points: 9 V Reference circuit1Component terminal 2 & Ground
    • If not between 8. 5 and 9. 5 V 

      Replace the component: Automatic Transmission Wiring Harness

    • Go to next step: If between 8. 5 and 9. 5 V 
  15. Ignition Off
  16. Install the special tool: EL-38522 Variable Signal Generator
    • Red lead @ Signal circuit terminal 1
    • Black lead @ Ground
    • Set the voltage to 5 V
    • Set the frequency to 300 Hz
    • Set the duty cycle to 50%
  17. Ignition - On / Vehicle - In Service Mode
  18. Verify the scan tool parameter: Transmission OSS = 230 to 280 RPM
    • If not between 230 and 280 RPM 

      Replace the component: Automatic Transmission Wiring Harness

    • Go to next step: If between 230 and 280 RPM 
  19. Remove the component: B14A Transmission Output Shaft Speed Sensor
  20. Inspect the following components: Output Carrier Assembly - Damaged or misaligned reluctor ring.
    • If a condition exists 

      Replace the component: Output Carrier Assembly

    • Go to next step: If no condition exists 
  21. Replace the component: B14A Transmission Output Shaft Speed Sensor
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