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Home >> Chevrolet >> 2021 >> Trailblazer RS, 4WD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 11 (Automatic Transmission - VT40 (MRG) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P0721-P0723, P077C, or P077D >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
    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 8.3 to 9.6 V between the test points: 9 V Reference circuit terminal 7 & Ground
    • If less than 8.3 V 
    1. Ignition/Vehicle - Off
    2. Disconnect the electrical connector: K71 Transmission Control Module
    3. Test for infinite resistance between the test points: 9 V Reference circuit terminal 7 @ 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 circuit terminal 7 @ Component harness & The other end of the circuit @ 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 9.6 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 circuit terminal 7 @ 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 8.3 and 9.6 V 
  5. Ignition/Vehicle - Off
  6. Install & Setup EL-38522 Variable Signal Generator
    • Voltage - 5 V
    • {Test 1} Frequency - 1k Hz
    • {Test 2} Frequency - 5k Hz
    • Duty Cycle - 20%
    • Black lead @ Ground
    • Red lead @ Signal circuit terminal 6
  7. Ignition - On / Vehicle - In Service Mode
  8. Verify the scan tool parameter:

    Test 1

    • Transmission OSS = 2200 to 2400 RPM
    • Transmission Output Speed Sensor Direction = Reverse
    • Transmission Output Speed Sensor Direction Signal = 0.20 ms

    Test 2

    • Transmission OSS = 8100 to 8300 RPM
    • Transmission Output Speed Sensor Direction = Forward
    • Transmission Output Speed Sensor Direction Signal = 0.04 ms
    • If not the specified values 
    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 6 @ 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 6 @ 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 6 @ Component harness & The other end of the circuit @ 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 the specified values 
  9. Ignition/Vehicle - Off
  10. Connect the electrical connector: X175
  11. Remove the component: Torque Converter and Differential Housing
  12. Disconnect the electrical connector: B14A Transmission Output Shaft Speed Sensor
  13. Ignition - On / Vehicle - In Service Mode
  14. Test for 8.3 to 9.6 V between the test points: 9 V Reference circuit terminal 1 & Ground
    • If not between 8.3 and 9.6 V 

      Replace the component: Automatic Transmission Wiring Harness

    • Go to next step: If between 8.3 and 9.6 V 
  15. Ignition/Vehicle - Off
  16. Install & Setup EL-38522 Variable Signal Generator
    • Voltage - 5 V
    • Frequency - 5k Hz
    • Duty Cycle - 20%
    • Black lead @ Ground
    • Red lead @ Signal circuit terminal 2
  17. Ignition - On / Vehicle - In Service Mode
  18. Verify the scan tool parameter: Transmission OSS = 8100 to 8300 RPM
    • If not between 8100 and 8300 RPM 

      Replace the component: Automatic Transmission Wiring Harness

    • Go to next step: If between 8100 and 8300 RPM 
  19. Replace the component: B14A Transmission Output Shaft Speed Sensor
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