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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 57 (Automatic Transmission - 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 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. 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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