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 P2636CIRCUIT/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.
- Ignition OFF, disconnect the fuel pump relay.
- Ignition ON, verify that a test lamp illuminates between the ground circuit terminal 85 and B+.
- If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance.
- Verify that a test lamp does not illuminate between the ground circuit terminal 85 and the control circuit terminal 86.
- If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Remove the test lamp.
- Command the fuel pump relay ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is OK.
- If not the specified value, test the fuel pump relay control circuit for a short to ground. If the circuit tests normal, replace the ECM.
- Install a 3A fused jumper wire between the fuel pump relay control circuit terminal 86 and the ground circuit terminal 85. Command the fuel pump ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is Fault.
- If not the specified value, test the fuel pump relay control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Inspect the fuel pump fuse.
- If the fuel pump fuse is open, test for the following conditions:
- A short to ground in the relay switch B+ circuit
- A short to ground in the supply voltage circuit of the fuel pump
- If the above circuits test normal, replace the fuel tank module.
- If the fuel pump fuse is open, test for the following conditions:
- Verify that a test light illuminates between the B+ circuit and ground.
- If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
- Connect a 15A fused jumper wire between the B+ circuit and the supply voltage circuit of the fuel pump. Verify the fuel pump is activated.
- If the fuel pump does not activate, test for the following conditions:
- An open/high resistance in the supply voltage circuit of the fuel pump
- An open/high resistance in the ground circuit of the fuel pump
- If the above circuits test normal, replace the fuel tank module.
- If the fuel pump does not activate, test for the following conditions:
- If all circuits test normal, test or replace the fuel pump 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:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.