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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 56 (Automatic Transmission - 6L90 (MYD) - 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: X1 @ Q8 Control Solenoid Valve Assembly
  3. Ignition - On / Vehicle - In Service Mode
  4. Test for 11 to 13 V between the test points: Signal circuit terminal 3 @ Component harness & Ground
    • If not between 11 and 13 V 
    1. Ignition/Vehicle - Off
    2. Disconnect the appropriate electrical connector: K20 Engine Control Module
    3. Test for infinite resistance between the test points: Signal circuit terminal 3 @ Component harness & 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: Signal circuit terminal 3 @ Component harness & The other end of the circuit
    • 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 
  5. Ignition/Vehicle - Off
  6. Remove the component: Control Valve Body Cover
  7. Connect the electrical connector: X1 @ Q8 Control Solenoid Valve Assembly
  8. Disconnect the electrical connector: X2 @ Q8 Control Solenoid Valve Assembly - B15 Transmission Internal Mode Switch
  9. Ignition/Vehicle - On
  10. Verify the scan tool parameter: Park/Neutral Position Switch = In Gear
    • If not the specified state 
    1. Test for 11 to 13 V between the test points: Signal circuit terminal 3 & Ground
      • If not between 11 and 13 V - Replace the component: Q8 Control Solenoid Valve Assembly
      • Go to next step: If between 11 and 13 V
    2. Replace the component: K20 Engine Control Module
  11. Connect a 3 A fused jumper wire between the test points: Signal circuit terminal A & Low Reference circuit terminal F
  12. Verify the scan tool parameter: Park/Neutral Position Switch = Park/Neutral
    • If not the specified state 
    1. Ignition/Vehicle - Off & Remove - Jumper wire(s)
    2. Disconnect the appropriate electrical connector: K20 Engine Control Module
    3. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points: Signal circuit terminal A @ Q8 Control Solenoid Valve Assembly & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    5. Ignition/Vehicle - Off
    6. Test for less than 2 ohms between the test points: Signal circuit terminal 3 @ Q8 Control Solenoid Valve Assembly & The other end of the circuit
      • 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 the specified state 
  13. Test or replace the component: B15 Transmission Internal Mode Switch
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