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 G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 700 (ENGINE CONTROLS AND FUEL - 3.6L - DTC P0201 TO DTC P0629)DTC P0627-P0629CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2010 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the fuel pump relay using the J 43244: Pliers.
- Connect a test lamp between the control circuit terminal 86 of the fuel pump relay and ground.
- Ignition ON, command the fuel pump ON and OFF with a scan tool. The test lamp should turn ON and OFF as commanded.
- If the test lamp remains OFF all the time, test for a short to ground or an open/high resistance on the control circuit. If the circuit/connections test normal, replace the ECM.
- If the test lamp remains ON all the time, test for a short to voltage on the control circuit. If the circuit/connections test normal, replace the ECM.
- Ignition OFF, connect a test lamp between the fuel pump relay control circuit terminal 86 and the ground circuit terminal 85 of the fuel pump relay.
- Ignition ON, command the fuel pump ON and OFF with a scan tool. The test lamp should turn ON and OFF as commanded.
- If the test lamp does not turn ON when commanded, repair the open/high resistance in the ground circuit of the fuel pump relay.
- Ignition ON, test for 2-3 V on the control circuit terminal 86 of the fuel pump relay.
- If not within the specified range, replace the ECM.
- If all circuits/connections 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.