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Home >> Buick >> 2015 >> Regal GS, AWD >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Automatic Transmission - 6T70 - Diagnostic Information And Procedures >> Diagnostic Information and Procedures >> DTC P0851: Park/Neutral Position Switch >> Circuit/System Testing

Circuit/System Testing

    NOTE:

    You must perform the Circuit/System Verification first.

  1. Ignition OFF, disconnect the X1 harness connector at the Q8 Control Solenoid Valve Assembly harness connector at the automatic transmission.
  2. Install the DT-47825-20  Adapter Harness to the vehicle harness connector.
    3. NOTE:

    All testing in steps 3 through 5 will be performed at the DT-47825-20  Adapter Harness connector.

  3. Test for less than 5Ω between the ground circuit terminal 18 and ground.
    • If 5Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2Ω in the ground circuit end to end.
    • If 2Ω or greater, repair the open/high resistance in the circuit.
    • If less than 2Ω, repair the open/high resistance in the ground connection.
    • If less than 5Ω 
  4. Ignition ON.
  5. Test for 11-13V between signal circuit terminal 20 and ground.
    • If not between 11-13V 
    1. Ignition OFF, remove the harness connector at the K20 Engine Control Module.
    2. Test for infinite resistance between signal circuit terminal 20 and ground.
    • If less than infinite resistance, repair the short to ground in the circuit.
    • If infinite resistance.
    1. Test for less than 2Ω in the signal circuit end to end.
    • If 2Ω or greater, repair the open/high resistance in the circuit.
    • If less than 2Ω, replace the K20 Engine Control Module.
    • If between 11-13V 
  6. Ignition OFF, transmission in Park, disconnect the DT-47825-20  Adapter Harness from the vehicle wire harness.
  7. Connect the DT-47825-20  Adapter Harness to the Q8 Control Solenoid Valve Assembly X1 connector.
    8. NOTE:

    The ignition will need to be ON momentarily to shift from Park.

  8. Test for less than 10Ω between the Park/Neutral signal circuit terminal 20 and ground circuit terminal 18 with the transmission in Park and Neutral.
    • If 10Ω or greater 
    1. Disconnect the DT-47825-20  Adapter Harness and remove the transmission control valve body cover.
    2. Install the DT-47825-20  Adapter Harness to the Q8 Control Solenoid Valve Assembly X1 connector.
    3. Disconnect the B15 Transmission Internal Mode Switch electrical connector from the Q8 Control Solenoid Valve Assembly.
    4. Test for less than 10Ω between Park/Neutral signal circuit terminal 20 and terminal A at the Q8 Control Solenoid Valve Assembly X2 connector.
      • If 10Ω or greater, replace the Q8 Control Solenoid Valve Assembly.
      • If less than 10Ω, replace the B15 Transmission Internal Mode Switch.
    • If less than 10Ω 
  9. Test for infinite resistance between the Park/Neutral signal circuit terminal 20 and ground circuit terminal 18 with the transmission in Reverse and Drive.
    • If less than infinite resistance 
    1. Disconnect the DT-47825-20  Adapter Harness and remove the transmission control valve body cover.
    2. Install the DT-47825-20  Adapter Harness to the Q8 Control Solenoid Valve Assembly X1 connector.
    3. Disconnect the B15 Transmission Internal Mode Switch electrical connector from the Q8 Control Solenoid Valve Assembly.
    4. Test for infinite resistance between the Park/Neutral signal circuit terminal 20 and ground circuit terminal 18.
      • If less than infinite resistance, replace the Q8 Control Solenoid Valve Assembly.
      • If infinite resistance, replace the B15 Transmission Internal Mode Switch.
    • If infinite resistance 
  10. Replace the K20 Engine Control Module.
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