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Home >> Chevrolet >> 2024 >> Tahoe Commercial, 4WD >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Automatic Transmission - 10L80 (MHS MHU MQC) - Diagnostic Information And Procedures (2 Of 2) >> Diagnostic Information and Procedures >> DTC P27EB, P27ED, or P27EE >> Circuit/System Testing

Circuit/System Testing

  1. Ignition/Vehicle - Off
  2. NOTE:

    When the following connector is disconnected, the ignition cannot be turned off due to lack of a valid park input to the TCM. If the ignition needs to be turned off, the connector will need to be reconnected.

  3. Disconnect the electrical connector: X1@T12 Automatic Transmission
  4. Ignition - On/Vehicle - In Service Mode
  5. Test for 8.8 to 9.2 V between the test points: 9 V Reference circuit terminal 8 & Ground
    • If less than 8.8 V 
    1. Disconnect the electrical connector: K71 Transmission Control Module
    2. Test for infinite resistance between the test points: 9 V Reference circuit terminal 8@Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 ohms between the test points: 9 V Reference circuit terminal 8@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 9.2 V 
    1. Disconnect the electrical connector: K71 Transmission Control Module
    2. Ignition - On/Vehicle - In Service Mode
    3. Test for less than 1 V between the test points: 9 V Reference circuit terminal 8@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 8.8 and 9.2 V 
  6. Install - EL-38522 Variable Signal Generator
    • Voltage - 5 V
    • Frequency - 10 kHz
    • Duty Cycle - 40%
    • Black lead@Battery Negative Post
    • Red lead@Signal circuit terminal 20
  7. Verify the scan tool parameter: Transmission Range Control Valve Position Sensor = 2.0 to 2.3 V
    • If less than 2.0 V 
    1. Remove - EL-38522 Variable Signal Generator
    2. Ignition/Vehicle - Off
    3. Disconnect the electrical connector: K71 Transmission Control Module
    4. Test for infinite resistance between the test points: Signal circuit terminal 20@Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    5. Test for less than 2 ohms between the test points: Signal circuit terminal 20@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 2.3 V 
    1. Disconnect the electrical connector: K71 Transmission Control Module
    2. Ignition - On/Vehicle - In Service Mode
    3. Test for less than 1 V between the test points: Signal circuit terminal 20@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 2.0 and 2.3 V 
  8. Remove the component: Automatic Transmission Fluid Pan
  9. Connect the electrical connector: X1@T12 Automatic Transmission
  10. Disconnect the electrical connector: X176
  11. Test for 8.8 to 9.2 V between the test points: 9 V Reference circuit terminal 11@Control module harness & Ground
    • If not between 8.8 and 9.2 V 

      Replace the appropriate component: Automatic Transmission Wiring Harness

    • Go to next step: If between 8.8 and 9.2 V 
  12. Install - EL-38522 Variable Signal Generator
    • Voltage - 5 V
    • Frequency - 10 kHz
    • Duty Cycle - 40%
    • Black lead@Battery Negative Post
    • Red lead@Signal circuit terminal 10
  13. Verify the scan tool parameter: Transmission Range Control Valve Position Sensor = 2.0 to 2.3 V
    • If not between 2.0 and 2.3 V 

      Replace the appropriate component: Automatic Transmission Wiring Harness

    • Go to next step: If between 2.0 and 2.3 V 
  14. Connect the electrical connector: X176
  15. Disconnect the electrical connector: X177
  16. Test for 8.8 to 9.2 V between the test points: 9 V Reference circuit terminal 6@Control module harness & Ground
    • If not between 8.8 and 9.2 V 

      Replace the appropriate component: Automatic Transmission Wiring Harness

    • Go to next step: If between 8.8 and 9.2 V 
  17. Install - EL-38522 Variable Signal Generator
    • Voltage - 5 V
    • Frequency - 10 kHz
    • Duty Cycle - 40%
    • Black lead@Battery Negative Post
    • Red lead@Signal circuit terminal 5
  18. Verify the scan tool parameter: Transmission Range Control Valve Position Sensor = 2.0 to 2.3 V
    • If not between 2.0 and 2.3 V 

      Replace the appropriate component: Automatic Transmission Wiring Harness

    • Go to next step: If between 2.0 and 2.3 V 
  19. Connect the electrical connector: X177
  20. Disconnect the electrical connector: B315A Transmission Range Control Valve 1 Position Switch
  21. Test for 8.8 to 9.2 V between the test points: 9 V Reference circuit terminal 1@Control module harness & Ground
    • If not between 8.8 and 9.2 V 

      Replace the appropriate component: Automatic Transmission Wiring Harness

    • Go to next step: If between 8.8 and 9.2 V 
  22. Install - EL-38522 Variable Signal Generator
    • Voltage - 5 V
    • Frequency - 10 kHz
    • Duty Cycle - 40%
    • Black lead@Battery Negative Post
    • Red lead@Signal circuit terminal 1
  23. Verify the scan tool parameter: Transmission Range Control Valve Position Sensor = 2.0 to 2.3 V
    • If not between 2.0 and 2.3 V 

      Replace the appropriate component: Automatic Transmission Wiring Harness

    • Go to next step: If between 2.0 and 2.3 V 
  24. Test or replace the component: B315A Transmission Range Control Valve 1 Position Switch