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 MANUALSCHEVROLET2025TAHOE PPV, 4WDREPAIR AND DIAGNOSIS (SINGLE PAGE)ELECTRICALCHARGING SYSTEMSBATTERY, STARTING SYSTEM AND CHARGING SYSTEM - DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC INFORMATION AND PROCEDURESDTC P0621CIRCUIT/SYSTEM TESTING
2025 Chevrolet Tahoe PPV, 4WD
Circuit/System Testing
2025 Chevrolet Tahoe PPV, 4WDSECTION Circuit/System Testing
- Verify a test lamp illuminates between the G13 Generator B+ circuit terminal A X2 and ground.
- If the test lamp does not illuminate and the circuit fuse is good
- Test circuit 2 for an open/high resistance.
- if an open/high resistance is found, repair the fault on the circuit.
- Go to next step: If an open or high resistance is not found
- Verify the fuse is not open and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
- Test circuit 2 for a short to ground.
- If a short to ground is found, repair the fault on the circuit.
- Go to next step: If a short to ground is not found.
- Replace the G13 Generator.
- Go to next step: If the test lamp illuminates
- Ignition Off, disconnect the X1 connector at the G13 Generator, engine running.
- Test for 1 V or greater between control circuit terminal 1 and ground.
- If less than 1 V
- Test circuit 25 for a short to ground.
- If a short to ground is found, repair the fault on the circuit.
- Go to next step: If a short to ground is not found
- Test circuit 25 for an open/high resistance.
- If an open/high resistance is found, repair the fault on the circuit.
- Go to next step: If an open or high resistance is not found
- Replace the K20 Engine Control Module.
- Go to next step: If 1 V or greater
- Ignition OFF, disconnect the appropriate connector at the K20 Engine Control Module.
- Ignition ON.
- Test for less than 1 V between control circuit terminal 1 at G13 Generator connector X1 and ground.
- If greater than 1 V
Repair the short to voltage on circuit 25.
- Go to next step: If 1 V or less
- If greater than 1 V
- Replace the G13 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.