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.
Charging System: Generator
The single generator system consists of the generator mounted on the top right of the engine (diesel) or top center of the engine (gas). The gas engines use a 3G 115-amp generator with a 2.71:1 pulley ratio. The 6.0L diesel engine uses a 6G 110-amp generator with a 2.79:1 pulley ratio.
The dual generator package consists of an upper/lower dual generator system. The 6.0L upper generator is a VR42 140-amp generator with a 2.79:1 pulley ratio. The 6.0L lower generator is a 4G 120-amp generator with a 3.00:1 pulley ratio. The upper and lower generators are not interchangeable.
A snowplow option is available (6.0L diesel only) that includes a VR42 140-amp generator with a 2.79:1 pulley ratio. The 6G and the VR42 are similar in appearance and use the same connectors, making them interchangeable. Identification between the different generators can be carried out by referring to the generator engineering number and the parts catalog.
In the single generator system, with the key in the ON position, voltage is supplied through the charging system warning indicator (in the instrument cluster [IC]) through the I circuit to the voltage regulator. The regulator grounds this circuit and the charging system warning indicator is illuminated. When the engine is started, the regulator removes the ground on this circuit and the charging system warning indicator turns off.
On the dual generator system, the powertrain control module (PCM) controls the charging system warning indicator and commands the lamp on if the PCM detects a concern on the monitored circuits.
The dual generator system is also monitored and controlled by the PCM. The PCM monitors both the upper and lower generator I circuits to determine the output of both generators and sets possible diagnostic trouble codes (DTCs). The PCM controls the lower generator by turning the lower generator off when the glow plug system is commanded on by the PCM to avoid possible damage (excessive voltage) to the glow plugs. As soon as the glow plug system stops cycling, the PCM powers up the lower generator.
The dual generators operate independently of each other. The control is through the internal voltage regulators. If one generator fails, the other generator can maintain system performance under light load conditions. Under a heavy load, the PCM detects a concern, sets a DTC and illuminates the charging system warning indicator.
The set voltage varies with temperature and is typically higher in cold temperatures than in warm temperatures. This allows for better battery recharge in the winter and reduces the chance of overcharging in the summer.
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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.