System Operation

Multifunction Electronic Modules

System Operation

Battery Saver

NOTE: The battery saver time-out is 1 minute if the vehicle has less than 201 km (125 mi).

NOTE: The battery saver does not control the parking lamps if the headlamp switch is in the PARKING LAMPS ON position.

To save battery voltage, the BCM (Body Control Module) provides automatic shut-off of the interior and exterior lamps after a time-out period when the ignition is off. The BCM (Body Control Module) monitors the ignition state and input from the RKE (Remote Keyless Entry) system to determine when to energize or de-energize the battery saver relay and to shut the power off to the lamps. A timer in the BCM (Body Control Module) starts when:

- the ignition changes to OFF,

- any door or liftgate becomes ajar while the ignition is off,

- an UNLOCK button of the RKE (Remote Keyless Entry) transmitter is pressed while the ignition is off,

- a valid keypad code is entered while the ignition is off,

- or the courtesy lamp switch (integrated into the FLM (Front Lighting Control Module)) is used to turn the courtesy lamps on while the ignition is off.

When 10 minutes have elapsed, the BCM (Body Control Module) automatically shuts off voltage to the lamps. The timer restarts (voltage is restored if the BCM (Body Control Module) is in battery saver mode) if:

- the ignition transitions out of OFF,

- any door or liftgate becomes ajar,

- the UNLOCK button of the RKE (Remote Keyless Entry) transmitter is pressed,

- a valid keypad code is entered,

- the courtesy lamp switch is pressed.

Post Crash Alert Function

The post crash alert is a function controlled by the BCM (Body Control Module). If the RCM (Restraints Control Module) determines an impact of enough severity (the air bags may or may not be deployed), the post crash alert function activates. The post crash alert function activates the hazard lamp function and cycles the horn on 3 times, then off for 4 seconds, and repeats this cycle until the battery is discharged or the function is turned off. The post crash alert function can be turned off by:
- pressing the hazard flasher lamp switch (which may need to be pressed twice).
- pressing the RKE (Remote Keyless Entry) transmitter UNLOCK button.
- pressing the RKE (Remote Keyless Entry) transmitter PANIC button.

Field Effect Transistor (FET) Protection

FET (Field-Effect Transistor) Protection

A FET (Field-Effect Transistor) 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 a 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 (Diagnostic Trouble Code) 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) circuit 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 (Diagnostic Trouble Code) U1000:00 should set (U1000:00 may or may not set) along with the short circuit DTC (Diagnostic Trouble Code) that was stored on the first failure. These DTCs (Diagnostic Trouble Codes) cannot be cleared until the vehicle is repaired. After the repair, it is necessary to clear the DTCs (Diagnostic Trouble Codes) using the Clear DTC (Diagnostic Trouble Code) operation on the scan tool, cycling the ignition, and run the BCM (Body Control Module) on-demand self-test. 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, DTC (Diagnostic Trouble Code) U3000:49 sets along with the associated short circuit DTC (Diagnostic Trouble Code). DTC (Diagnostic Trouble Code) 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 (Powertrain Control Module) over the HS-CAN (High Speed Controller Area Network), converts the data into a MS-CAN (Medium Speed Controller Area Network) message and sends (gateways) the message to other network modules such as the HVAC (Heating, Ventilation, and Air Conditioning) module. 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)).