The generator control module, also referred to as the starter generator control module, is a serviceable GMLAN device located under the hood, toward the front of the vehicle on the drivers side. It is connected to the vehicles 12 and 36-volt DC power circuits, and it is also joined to the starter-generator by 3-phase AC cables. The generator control module is cooled by engine coolant, which is circulated through a cold plate. A separate, electrically driven pump is used to ensure adequate coolant flow, and individual coolant inlet and outlet hoses connect the cold plate to the cooling system. The generator control module performs three main functions:

1. As the power inverter for the starter-generator, the generator control module converts 36-volt DC power into 3-phase AC power to drive the starter-generator as a motor. The power inverter also rectifies 36-volt AC output power from the starter-generator into the 36-volt DC power used to charge the 36-volt generator battery.
2. An auxiliary power module contained within the generator control module converts 36-volt DC power into the 12-volt DC power which is used for 12-volt vehicle loads and to charge the underhood 12-volt battery. A serviceable 175 Amp Fuse (GM P/N 15305191) located beneath the generator control module DC cable terminal box cover protects the vehicles 12-volt electrical system from excessive current.
3. The generator control module contains a Renesas M32 processor, and it directly controls the starter-generator, transmission auxiliary oil pump, hill-hold solenoids, auxiliary coolant pump and the generator control module coolant pump. The pumps and solenoids are driven by 12-volt pulse width modulated (PWM) power through vehicle wiring harnesses.

The starter generator, sometimes referred to as the motor generator unit (MGU), is a serviceable 16 pole, permanent magnet, enhanced Lundell AC machine. This device not only serves as a 36-volt AC generator, it is also used to provide engine power assist and to start the engine following hybrid "autostops". 36-volt AC power flows between the starter generator and the generator control module through a three phase cable assembly.

As a generator, the starter-generator provides up to 3 KW of AC power to the generator control module power inverter. Field current is provided by the generator control module through a seven pin connector, and starter generator RPM feedback is transmitted back to the controller through the same connector. Starter generator temperature data is provided to the generator control module through a separate three pin connector.

As a motor, the machine provides up to 65 N·m of torque for power assist and engine starting. The motor receives three phase AC power from the power inverter within the generator control module.

The engine control module (ECM) will send an AutoStop state message to the body control module (BCM). The BCM will transmit the AutoStop state message to the instrument panel cluster (IPC). If all of the following conditions are true the indicated state will be Avail, otherwise the state will be Unavail:

The AutoStop ready indication will be a DIC message that indicates the following two states

The generator control module coolant pump is a serviceable component which is connected to the vehicle cooling system and the module cold plate using separate, serviceable hoses. The pump augments the engine driven water pump to ensure adequate coolant flow to the cold plate.

Three cables carry 36-volt AC power between the generator control module and the starter generator. The cables are serviceable as an assembly which includes the generator control module AC terminal box. The cables are shrouded in a blue conduit to alert the technician to the presence of intermediate voltage electrical energy.