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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 2159 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 4.8L, 5.3L, 6.0L, 6.2L - DTC P1255 TO DTC P3449)DTC P1682CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6

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 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
  1. Ignition ON, observe the scan tool Ignition 1 Signal and the EC Ignition Relay Feedback parameter to determine which is more than 3 V lower than the other.
    2. NOTE: The Ignition 1 Signal is supplied by the Run/Crank relay. The EC Ignition Relay Feedback signal is supplied by the powertrain relay.
  2. Ignition OFF, remove the relay that corresponds to the scan tool parameter that is more than 3 V lower.
    3. NOTE: A resistance of 6 Ξ© or greater in the circuit/underhood fuse block will cause the DTC to set.
  3. Ignition ON, connect a 20 A fused jumper wire between B+ and the applicable ignition voltage circuit terminal 87. Verify that the applicable scan tool parameter displays between 9-14 V.
    • If less than the specified value, test the ignition voltage circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.
  4. Ignition OFF, connect a DMM set to the diode setting between the control circuit terminal 86 and ground. Verify the DMM displays OL.
    • If not the specified value, test the control circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.
  5. Ignition ON, verify the DMM displays less than 1 V.
    • If not the specified range, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM.
  6. If all circuits test normal, replace the appropriate relay.
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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.