Principles of Operation

Body Control Module (BCM)

Principles of Operation

The Body Control Module (BCM) controls various systems by monitoring inputs from switches, sensors and messages sent from other modules. The BCM (Body Control Module) activates outputs based on the inputs received. For example, the Steering Column Control Module (SCCM) monitors the headlamp switch and transmits the headlamp switch position to the BCM (Body Control Module) over the network. Based on this input, the BCM (Body Control Module) may provide voltage to the exterior lamps.

Field-Effect Transistor (FET) Protection

A Field-Effect Transistor (FET) is a type of transistor that, when used with module software, monitors and controls current flow on module outputs. The FET (Field-Effect Transistor) protection strategy prevents module damage in the event of excessive current flow.

The BCM (Body Control Module) utilizes an FET (Field-Effect Transistor) protective circuit strategy for many of its outputs (for example, a headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET (Field-Effect Transistor) protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (FET (Field-Effect Transistor) protection) and the circuit is still shorted, the FET (Field-Effect Transistor) protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. Each FET (Field-Effect Transistor) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET (Field-Effect Transistor) and the ability of the FET (Field-Effect Transistor) to withstand it. A module lifetime level of fault events is established based upon the durability of the FET (Field-Effect Transistor). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, DTC U1000:00 should set along with the short circuit DTC that was stored on the first failure. These DTCs cannot be cleared until the vehicle is repaired.

After the repair, it is necessary for the module successfully complete a self-test (the module no longer detects the fault), to clear the DTCs using the Clear DTC operation on the scan tool, and then cycling the ignition for the circuit function to return.

The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur. If the number of short circuit fault events reach the third level, then DTCs U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and the module must be replaced after the initial fault is repaired.

Gateway Function

The BCM (Body Control Module) acts as a gateway module by receiving information in one format and transmitting it to other modules using another format. For example, the BCM (Body Control Module) receives the vehicle speed data from the PCM over the High Speed Controller Area Network (HS-CAN), converts the data into a Medium Speed Controller Area Network (MS-CAN) message and sends (gateways) the message to other network modules such as the HVAC module and the Audio Control Module (ACM). This enables network communication between modules that do not communicate using the same network (HS-CAN (High Speed Controller Area Network) or MS-CAN (Medium Speed Controller Area Network) ).