Circuit/System Testing

2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Circuit/System Testing
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: If the interior backlighting is malfunctioning, refer to Interior Backlighting Does Not Dim or Interior Backlighting Inoperative before performing this diagnostic.
  1. Ignition OFF, disconnect the harness connector at the PTO switch.
  2. Connect a test lamp between LED dimming supply circuit terminal 7 and ground.
  3. Ignition OFF, turn the headlamps ON and OFF. The test lamp should turn ON and OFF accordingly with the headlamp switch.
    • If the test lamp is always ON, test the LED dimming supply circuit for a short to voltage.
    • If the test lamp is always OFF, test the LED dimming supply circuit for a short to ground or an open/high resistance.
  4. Ignition ON, verify that a test lamp does not illuminate between the PTO switch indicator control circuit terminal 8 and ground.
    • If the test lamp illuminates, test the PTO switch indicator control circuit for a short to voltage. If the circuit tests normal, test or replace the PTO module.
  5. Ignition OFF, PTO OFF, verify that a test lamp does not illuminate between the PTO switch indicator control circuit and B+.
    • If the test lamp illuminates, test the PTO switch indicator control circuit for a short to ground. If the circuit tests normal, test or replace the PTO module.
  6. Ignition OFF, disconnect the harness connector at the PTO module.
  7. Ignition OFF, test for less than 1.0 ohm of resistance on the PTO switch indicator control circuit between the PTO switch terminal 8 and the PTO module terminal 9.
    • If greater than the specified range, test the PTO switch indicator control circuit for an open/high resistance.
  8. If all circuits test normal, test or replace the PTO switch.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.