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Home >> Cadillac >> 2019 >> CTS Base, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 68 (Automatic Transmission - 8L45 (M5N) Or 8L90 (M5U) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P0851 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2018 Cadillac CTS. 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. Test for less than 5 ohms between the test points: Terminal 30 & Ground
    • If 5 ohms or greater 
    1. Disconnect the electrical connector: K71 Transmission Control Module
    2. Test for less than 2 ohms between the test points: Terminal 30@X175 & Terminal 25@K71 Transmission Control Module
      • 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 less than 5 ohms 
  4. Ignition - On / Vehicle - In Service Mode
  5. Test for 11 to 13 V between the test points: Terminal 35 & Ground
    • If not between 11 and 13 V 
    1. Ignition/Vehicle & All vehicle systems - Off
    2. Disconnect the electrical connector: X1@K20 Engine Control Module
    3. Test for infinite resistance between the test points: Terminal 35@X175 & 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: Terminal 35@X175 & The other end of the circuit@K20 Engine Control Module
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component: K20 Engine Control Module
    • Go to next step: If between 11 and 13 V 
  6. Connect a 3 A fused jumper wire between the test points: Terminal 35 & Terminal 30@X175
  7. Verify the scan tool parameter: Park/Neutral Position Switch = Park/Neutral
    • If not the specified state 

      Replace the component: K20 Engine Control Module

    • Go to next step: If the specified state 

      Go to next step: Test or replace the component: B15 Transmission Internal Mode Switch

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