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Home >> GMC >> 2017 >> Acadia SL >> Repair and Diagnosis >> External Pages >> Different car >> Section 197 (Automatic Transmission - 8L45 (M5N M5T) Or 8L90 (M5U) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P0851: Park/Neutral Position Switch >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition Off and all vehicle systems Off, disconnect the X175 harness connector at the T12 Automatic Transmission Assembly. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 5 Ω between the ground circuit terminal 30, and ground.
    • If 5 Ω or greater 
    1. Disconnect the harness connector at the K71 Transmission Control Module.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K71 Transmission Control Module.
    • If less than 5 Ω 
  3. Ignition On.
  4. Test for 11-13 V at the signal circuit terminal 35 and ground.
    • If not between 11-13 V 
    1. Ignition Off, disconnect the X1 harness connector at the K20 Engine Control Module.
    2. Test for infinite resistance between the harness connector X175, terminal 35 and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
    • If between 11-13 V 
  5. Connect a 3 A fused jumper wire between signal circuit terminal 35 and the ground circuit terminal 30.
  6. Verify the scan tool park/neutral position switch parameter displays Park/Neutral.
    • If Park/Neutral is not displayed 

      Replace the K20 Engine Control Module.

    • If Park/Neutral is displayed 
  7. Perform the Component Testing.
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