GM Service Manual Online
For 1990-2009 cars only

Generator Battery Control Module (GBCM)

Parameter

System State

Expected Value

Description

Operating Conditions: Ignition ON/Engine OFF

Battery Voltage Signal

--

12.3 V

The scan tool displays 0-20 volts. The scan tool displays the voltage as received by the module.

Generator L Terminal Signal Command

--

0 Percent

The scan tool displays On/Off. The scan tool displays Off until the engine is running, at which time it will display On.

Regulated Voltage Control Current Sensor

--

Varies

The scan tool displays Amps. This controls how much current is going to or from the negative battery cable.

Running State of Charge

--

Varies

The scan tool displays percent. This calculates the battery's state of charge based on current and voltage over a long period of time.


Generator Battery Control Module Output Controls

Output Control

Description

GEN L-Terminal

The engine control module (ECM) commands the generator OFF by removing the 5-volt reference signal from the L terminal of the voltage regulator when you select OFF. The generator will then stop generating an output voltage.