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 500 (BATTERY, CHARGING SYSTEM AND STARTING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURES (BATTERY, CHARGING SYSTEM AND STARTING SYSTEM)DTC P0621 (GAS)(BATTERY, CHARGING SYSTEM AND STARTING SYSTEM)CIRCUIT/SYSTEM TESTING (GAS)(BATTERY, CHARGING SYSTEM AND STARTING SYSTEM)
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing (Gas)(Battery, Charging System And Starting System)
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing (Gas)(Battery, Charging System And Starting System)
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2009 GMC Savana Special, 2009 GMC Savana Camper Special, 2009 GMC Savana, 2009 Chevrolet RV Cutaway, and 2009 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the harness connector at the generator.
- Ignition ON, test for less than 1 volt between the generator turn on signal circuit terminal B X1 and ground.
- If greater than the specified range, test the generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Engine running, test for greater than 3.5 volts between the generator turn on signal circuit terminal B and ground.
- If less than the specified range, test the generator turn on signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- If the circuit tests normal, test or replace the generator.
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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.