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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 2 (Automatic Transmission - 8L90 (M5U MQD) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> Tow/Haul Switch/Indicator Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
  1. Ignition/Vehicle - Off
  2. Disconnect the electrical connector: S18 Exhaust Brake Switch
  3. Test for infinite resistance between the test points: Signal circuit terminal D (component side) & Ground circuit terminal A (component side)
    • If less than infinite resistance 

      Replace the component: S18 Exhaust Brake Switch

    • Go to next step: If infinite resistance 
  4. Press and hold the switch: S18 Exhaust Brake Switch

    Test for less than 5 ohms between the test points: Signal circuit terminal D (component side) & Ground circuit terminal A (component side)

    • If 5 ohms or greater 

      Replace the component: S18 Exhaust Brake Switch

    • Go to next step: If less than 5 ohms 
  5. Test for less than 10 ohms between the test points: Ground circuit terminal A (harness side) & Ground
    • If 10 ohms or greater 
    1. Disconnect the ground connection: G302
    2. Test for less than 2 ohms between the test points: Ground circuit terminal A (harness side) & Terminal G220
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 ohms 
  6. Disconnect the electrical connector: X1 @ K9 Body Control Module
  7. Ignition - On / Vehicle - In Service Mode
  8. Test for less than 1 V between the test points: Signal circuit terminal D (harness side) @ S18 Exhaust Brake Switch & Ground
    • If 1 V or greater 

      Repair the short to voltage on the circuit.

    • Go to next step: If less than 1 V 
  9. Ignition/Vehicle - Off
  10. Test for infinite resistance between the test points: Signal circuit terminal D (harness side) @ S18 Exhaust Brake Switch & Ground
    • If less than infinite resistance 

      Repair the short to ground on the circuit.

    • Go to next step: If infinite resistance 
  11. Test for less than 5 ohms between the test points: Signal circuit terminal D (harness side) @ S18 Exhaust Brake Switch & The other end of the circuit @ Control module harness
    • If 5 ohms or greater 

      Repair the open/high resistance in the circuit.

    • Go to next step: If less than 5 ohms 
  12. Replace the component: K9 Body Control Module
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