Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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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 P2635CIRCUIT/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.
- Verify that DTCs P018C, P018D, P0231, P0232, or P023F are not set.
- If the DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
- Ignition OFF, disconnect the harness connector at the G12 fuel pump.
- Ignition OFF, test for less than 5.0 Ξ© between the G12 fuel pump low reference circuit terminal A and ground.
- If greater than the specified range, test the G12 fuel pump low reference circuit for a high resistance. If the circuit tests normal, replace the K27 fuel pump control module.
- Ignition OFF, install a test lamp between the control circuit terminal D and the low reference circuit terminal A.
- Ignition ON, command the Fuel Pump Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K27 fuel pump control module.
- If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K27 fuel pump control module.
- Perform the Fuel System Diagnosis (Without FPCM)
or Fuel System Diagnosis (FPCM)
to verify proper fuel pressure.
- If the fuel pressure is not normal, replace the G12 fuel pump
- If all circuits test normal, replace the K27 fuel pump control module.
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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.