Body Control Systems: Description and Operation
Multifunction Electronic Modules
Component Location
Overview
The BCM (Body Control Module) controls the following:
- Battery saver function
- Brake shift interlock
- Delayed accessory function
- Dimmable backlighting
- Exterior lighting
- Horn
- Ignition state messaging
- Interior lighting
- Keyless entry keypad (without IA (Intelligent Access))
- Liftgate release (without IA (Intelligent Access))
- PATS (Passive Anti-Theft System) (vehicles without IA (Intelligent Access))
- Perimeter alarm
- Power door locks (vehicles without IA (Intelligent Access))
- Post crash alert function
- RKE (Remote Keyless Entry) system (without IA (Intelligent Access))
- Remote start
- TPMS (Tire Pressure Monitoring System)
The RFA (Remote Function Actuator) (with IA (Intelligent Access) only) controls the following:
- IA (Intelligent Access) function
- Key validation (part of the PATS (Passive Anti-Theft System))
- Keyless entry keypad
- Liftgate release
- PATS (Passive Anti-Theft System)
- Power door locks
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
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, the short circuit DTC (Diagnostic Trouble Code) that was stored on the first failure cannot be cleared by a command to clear the continuous DTCs (Diagnostic Trouble Codes). The module does not allow this code to be cleared or the circuit restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs (Diagnostic Trouble Codes) present), DTC (Diagnostic Trouble Code) U1000:00 and the associated DTC (Diagnostic Trouble Code) (the DTC (Diagnostic Trouble Code) related to the shorted circuit) automatically clears and the circuit function returns.
When each level is reached, the DTC (Diagnostic Trouble Code) associated with the short circuit sets along with DTC (Diagnostic Trouble Code) U1000:00. These DTCs (Diagnostic Trouble Codes) are cleared using the module on-demand self-test, then the Clear DTC (Diagnostic Trouble Code) operation on the scan tool (if the on-demand test shows the fault corrected). 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 (Diagnostic Trouble Codes) U1000:00 and U3000:49 set 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 repair.
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)).
Component Description
Body Control Module (BCM)
The BCM (Body Control Module) is a multifunction module that requires a PMI (Programmable Module Installation) when replaced. For additional information, REFER to Programmable Module Installation (PMI) Module Configuration.
Remote Function Actuator (RFA)
The RFA (Remote Function Actuator) is a multifunction module that requires a PMI (Programmable Module Installation) when replaced. For additional information, REFER to Programmable Module Installation (PMI) Module Configuration.