Body Control Module: Description and Operation
Description
General
The Body Control Unit (BCU) is located behind the passenger glovebox and is connected to the main harness by four connectors on its bottom edge and an additional connector located on the side of the BCU casing. Mounting the BCU behind the fascia makes it reasonably inaccessible for intruders to disable the anti-theft system.
The BCU uses solid-state microprocessor control to perform logical operations and timing functions for a variety of the vehicle's electrically operated systems, these include:
^ Door locking.
^ Anti-theft alarm and immobilisation system.
^ Exterior lighting including direction indicators and hazard warning lamps.
^ Courtesy lighting.
^ Wipers and washers.
^ Electric windows and sunroof.
^ Heated windows.
The BCU also communicates with several other electronically controlled systems such as the EAT ECU and SLABS ECU and also has a datalink between the Intelligent Driver Module (IDM) and the instrument pack. The datalink is a low speed bus capable of transmitting and receiving messages at a data rate of 10,400 bits per second. Additional inputs and outputs to peripheral devices are included which are necessary for determining vehicle status for particular logical operations e.g. crank, ignition key inserted, fuel flap enable etc.
The BCU receives its power supply from the engine compartment fuse box, and is protected by a 10 A fuse. The BCU communicates with the IDM to provide the control signals to perform power switching operations in conjunction with dedicated relays.
IDM
The IDM is integrated into the passenger compartment fuse box, which is mounted behind the fascia below the steering column. There are no harnesses between the fuse box and the IDM. The IDM performs the power switching operations for several of the vehicle's electrical systems.
The IDM communicates with the BCU and the instrument pack via a serial interface. If the BCU or the IDM is replaced, the communications link between the two units has to be re-established. This can be done either by switching on the ignition and leaving it on for five minutes, or by using TestBook. The vehicle immobilisation will remain active until the communications link between the BCU and IDM has been re-established.
Transit mode
To prevent excessive battery drain during transit to overseas markets, the vehicle is placed in a transit mode. The following functions are disabled when the vehicle is in transit mode:
^ Volumetric sensors.
^ Passive immobilisation.
^ Immobilisation of the vehicle by use of door lock.
^ Ignition key interlock.
^ Electric seat enable time-out with driver's door open.
Power supply
Battery supply to the BCU and the IDM is provided through a 10 A fuse located in the engine compartment fuse box.
The BCU unit receives an ignition switched power supply (ignition switch position II) input via a 10 A fuse in the passenger compartment fuse box.
The BCU receives a signal when the ignition switch is turned to the crank position, it then supplies an earth path to the starter relay coil, to enable the crank operation by supplying power through the starter relay contacts to the starter motor.
Battery voltage is monitored and BCU operation will function normally between 8 and 18 volts. Between 5.7 and 8 volts the BCU is in the 'under volts' state. The status of the battery is used to determine which outputs may be driven.
If a voltage supply above 18 volts is experienced, outputs will not normally be driven except for those functions which are required during cranking (robust immobilisation, antenna coil, crank enable relay and feed to gear position switch contacts W, X, Y, Z). In the over voltage state the vehicle can be driven, but all other functions are disabled and outputs are switched off (power windows, heated screen, direction indicators etc.).
All functions are disabled on power up until communications between the BCU and IDM have been established. If communications cannot be established, operation will commence with degraded functionality.
Battery supply to the IDM is provided through the inertia switch and a 10 A fuse in the engine compartment fuse box. If the inertia switch contacts are closed battery voltage is available at the IDM; if the inertia switch contacts are open there is no battery supply to the IDM. The supply condition of the IDM is signalled to the BCU via the serial bus. If the inertia switch is operated (contacts open) the change in state is detected by the BCU which unlocks the doors if the ignition switch is in position II and the alarm is not set.
The BCU is earthed through a hard-wire connection.
Inputs and Outputs
The BCU and IDM process inputs and provide the necessary outputs for control and operation of the vehicle's 'body systems.
BCU inputs
The BCU processes signals received from the following components:
^ Door latch switches.
^ Driver's door key lock/unlock switches.
^ Bonnet activated security system.
^ Volumetric sensors.
^ Central Door Locking (CDL) switches.
^ Remote transmitter (via receiver unit).
^ Inertia fuel cut-off switch.
^ Ignition switch.
^ Fuel flap release switch.
The input voltages (Vin) for BCU digital signals are defined as follows:
^ Logic 1 when Vin > 6 V.
^ Logic 0 when Vin < 2 V.
BCU input voltages between 2 and 6 volts are indeterminate and cannot be guaranteed.
Analogue input voltages are measured as a ratio with respect to battery voltage.
BCU outputs
The BCU processes the input signals it receives and uses the information to determine the control outputs that need to be established for any given set of conditions. The BCU provides controlled outputs for the following systems:
^ Interior courtesy lamps.
^ Fuel flap release actuator.
^ Anti-theft status LED.
^ Engine Control Module.
^ Door lock actuators.
^ Direction indicators and hazard warning lamps.
^ Headlamps.
^ Alarm sounder.
^ Vehicle horns.
^ Battery backed sounder.
^ Starter relay.
^ Passive re-mobilisation exciter coil.
Simultaneous switching of outputs in different units is limited by the bus transfer time, but the skew is no longer than 100 ms for either the BCU or the IDM. When the processor is reset, all outputs are switched off until the inputs have been read for the first time to check current condition.
The pinout details for the BCU connectors are defined below:
C0660 Connector Pin Details:
C0661 Connector Pin Details:
C0662 Connector Pin Details:
C0663 Connector Pin Details:
C0664 Connector Pin Details:
IDM Inputs
The IDM inputs are communicated to the BCU using the serial datalink so that the BCU can perform the necessary logic operations:
The Vin for IDM digital signals are defined as follows:
^ Logic 1 when Vin > 8 V.
^ Logic 0 when Vin < 2 V.
IDM input voltages between 2 and 8 volts are indeterminate and cannot be guaranteed.
IDM Outputs
The IDM receives the following signals from the BCU using the serial datalink to provide power outputs:
Diagnostic Socket
The BCU has a serial connection to the diagnostic socket to allow unit interrogation using TestBook.
In addition to fault diagnosis, the BCU can be programmed with the following information:
^ Pup codes.
^ Options.
^ VIN code.
^ EKA code.
^ EEPROM locking.
The following manufacturing details are programmed into the BCU which can be accessed using TestBook:
^ Date of manufacture.
^ Hardware version number.
^ Unit serial number.
^ Odometer reading.
It is not possible to use the diagnostic bus to communicate with the BCU via TestBook when the security system is active (except for passive immobilisation). This is a security measure to ensure that no key programming or market configuration can take place if the operator is not in possession of a valid remote transmitter or the vehicle keys.
The BCU is normally programmed to accept two remote transmitters, but a further two remote handsets can be programmed into the BCU and one optional Self Levelling Suspension (SLS) transmitter. All remote transmitters need to be available if TestBook is to be used to re-configure the BCU.
Programmable Options
The BCU can be programmed with a number of options to satisfy specific market requirements and customer preferences. The options can be set using TestBook.
Anti-Theft System
The BCU controls the logical switching operations for enabling and activating the anti-theft system. Features include:
- Perimetric protection - monitors the condition of doors and hinged panels.
^ Volumetric protection - monitors the vehicle's interior space.
^ Remote locking, superlocking and unlocking functions.
^ Engine immobilisation and remobilisation.
^ Advanced mislock detection and automatic compensation.
^ EKA code functions.
^ Customer configuration options.
^ Market configuration options.
Immobilisation
The immobilisation system comprises the following components:
^ RF receiver.
^ RF transmitter/transponder.
^ Transponder coil.
^ BCU.
^ Door switches, door lock switches and bonnet switch.
^ IDM.
^ ECM.
^ Starter solenoid relay.
^ Status LED.
Alarm system
The alarm system comprises the following components:
^ RF receiver.
^ RF transmitter.
^ BCU.
^ IDM.
^ Door switches, door lock switches and bonnet switch.
^ Battery backed-up sounder (BBUS).
^ Status LED.
On non NAS vehicles, power supply for the alarm sounder and the battery BBUS is provided through two relays in the passenger compartment fuse box. Each of the coils of the alarm relays are directly connected to the IDM which controls their operation under the direction of BCU signals received via the serial data bus.
On NAS vehicles, an audible warning is provided through operation of the vehicle horns. The BCU provides an earth path for the coil of the horn relay to initiate vehicle horn operation.
Central Door Locking (CDL)
The BCU carries out the logic control operation for CDL. A CDL switch is mounted on the fascia panel and has two inputs to the BCU, one for lock and one for unlock.
Door locking and unlocking can be performed using the remote transmitter in the keys and the receiver unit located above the vehicle's headlining, behind the rear sunroof aperture. The receiver detects the signals sent from the remote transmitter and sends a decoded signal to the BCU for processing.
Four methods of door locking are available:
^ Remote handset locking.
^ Vehicle key locking.
^ CDL switch locking.
^ Speed related locking.
Two security levels of door locking are available, CDL and Superlocking. The anti-theft alarm system works in conjunction with the CDL system.
Electric Windows and Sunroof
The BCU controls the logical operations and the timing periods for the electric front windows. The rear windows are hard-wired and the two electric sunroofs are controlled by a dedicated ECU which is enabled by the BCU.
The front windows are electrically operated using two rocker switches located in the center console. Electric motors are located in each of the front doors.
The rear windows are enabled by the IDM controlling the operation of the rear window relay located in the passenger compartment fuse box.
Wipers and Washers
The wiper and washer functions are controlled by the BCU and the IDM.
The front wipers and washers are operated from the switch stalk located on the right hand side of the steering column and only operate when the ignition switch is in position I or II. The front wipers are operated by a motor located below the windscreen plenum.
The BCU controls the wiper motor frequency of operation via the IDM when intermittent wipe or wash is selected. The front intermittent wipe option features five different intermittent delay periods. The shortest delay period is 3 seconds and this is increased by 2 second increments up to a maximum delay of 11 seconds. The desired delay period for the front wipers is set by the position of the rotary switch located on the wiper column stalk.
The rear wiper switch is located on the instrument pack cowl and is latched when pressed. The rear wiper electric motor is located in the tail door. The rear wiper operation is controlled according to a programmed strategy via the BCU and the IDM. The BCU also checks for a signal from either the reverse lamp switch located in the vehicle gearbox (manual gearbox models) or the gear position switch (automatic gearbox models) for operating the rear wipers when the vehicle is in reverse. The rear wiper and washer only operate when the ignition switch is in position II.
The front and rear washer pumps and the headlamp powerwash (where fitted) are also controlled through the BCU. The washers are operated from electric pumps attached to the washer reservoir located in the left hand wheel arch. The front wash switch is located on the wiper column stalk and is pulled towards the steering wheel to select the washer function. When the front washers are operated, the wipers are also activated for three full cycles. The rear wash switch is located on the instrument pack cowl. The BCU programme can be configured in one of two modes of operation:
^ No wiper operation when the wash switch is pressed.
^ Wiper action after an initial delay of 400 ms.
Headlamp wash is activated by the BCU via the IDM and operates when the headlamps are on and the front washers function is selected.
Electric seats
The BCU controls the logical operation of the electrically operated front seats. Two modes of operation are available:
^ Electric seat adjustment is enabled if the ignition is on or the driver's door is opened for a short time period.
^ Electric seat adjustment is enabled if the ignition is on and the driver's door is closed.
The seats are operated by four electric motors which control the seat cushion rear up/ down, the seat cushion front up/down, seat cushion forward/rearward and seat squab recline. The electrically powered lumbar adjustment in each seat is operated by a single motorised air pump and a solenoid located on the seat squab frame. The air pump inflates a cushion in the seat squab and the solenoid operates a valve to deflate the cushion. The seat squab and cushion may also contain heater elements to provide heated seat operation.
The switches for electrically operated seats are located either side of the center console.
Direction Indicators and Hazard warning Lamps
The direction indicator lamps are operated from a three position direction indicator switch on the left hand, steering column stalk. The BCU only allows the lamps to work as direction indicators when the ignition switch is in position II. The BCU also controls the lamps to operate as hazard warning lamps and as a visual warning for the anti-theft system, in which cases all lamps flash simultaneously irrespective of the ignition switch position.
System control of the direction indicators and hazard warning lamps is provided by the BCU operating with the IDM and two electronic relays located in the passenger compartment fuse box. The IDM and relays are integral parts of the passenger compartment fuse box and cannot be serviced individually. The serial data bus is used for communication of status and operation requests between the BCU, IDM and instrument pack.
The hazard warning lamps are operated from a latching pushbutton switch located on the fascia. All direction indicator/hazard warning lamp bulbs are rated at 5 Watts.
Headlamps
The BCU contains a feature which allow the vehicle headlamps to be turned on when the remote transmitter is pressed (courtesy headlamps).
For markets with daylight running lamps, the BCU controls the logical operation of the daylight running lamps. Options are daylight running lamps are on if the main beam headlamps are off, or the daylight running lamps are on with main and dipped beam off and the gearbox not in Park.
Front Fog Lamps
For markets with front fog lamps fitted, the BCU controls the operation of the front fog lamps. Options can be selected so that the fog lamps will operate with or without the headlamps on main beam.
Instrument pack
The BCU communicates with the instrument pack via a serial data bus.
^ The instrument pack provides the BCU and IDM with details of vehicle speed.
^ Signals are provided from the IDM to the instrument pack and BCU when the direction indicator lamps are active.
^ For certain markets, the BCU provides a signal to the instrument pack for indicating when the transfer box is in neutral.
^ The IDM can signal the instrument pack to illuminate a trailer warning lamp. This operates when the IDM senses that the current drawn by the indicator circuit exceeds a preset threshold.
^ The odometer reading displayed on the instrument pack LCD screen is also stored in non volatile memory in the BCU. Whenever the ignition is turned from position I to position II the instrument pack and the BCU compare their stored values.
^ The gear selector position is displayed on the instrument pack LCD screen under the direction of the BCU.
Starting
The starting system comprises a starter motor and solenoid located at the rear right hand side of the engine. A starter relay controlled by the BCU is used to supply battery power for starter solenoid operation. The starter motor receives its feed directly from the battery.
Cruise control
The BCU processes several signals used for cruise control:
^ When the brake pedal is pressed, a low voltage brake lamp signal is sent via the BCU to the cruise control ECU.
^ The gear position switch sends an input via the BCU to the cruise control ECU if the selector lever is in Park, Neutral or Reverse.
^ A voltage supply is fed from the BCU to the cruise control SET+ switch.
^ A voltage supply is fed from the BCU to the cruise control RES switch.
On vehicles with automatic transmission, if the BCU receives an input from the gear position switch or the brake pedal switch, the BCU sends a signal to the cruise control ECU to cancel or inhibit cruise control operation.
Shift Interlock (where fitted)
On automatic gearbox models, the BCU and IDM combine with an interlock relay located in the passenger compartment fuse box to operate a shift interlock solenoid, so that the gear selector lever cannot be moved out of Park until certain logical conditions have been satisfied. Operation of the interlock may be affected, if the battery becomes discharged.
Ignition Key Interlock (where fitted)
On automatic gearbox models, the ignition key interlock solenoid prevents removal of the ignition key from the ignition switch when the transmission gear selector is not in the Park position. The logic control operation for this is performed by the BCU.
Transfer Box Interlock (where fitted)
On Automatic Gearbox models, a transfer box interlock solenoid is controlled by the IDM to prevent transfer box shift lever being moved out of high or low range unless certain conditions have been satisfied. The IDM controls the operation of the transfer box relay which is located in the passenger compartment fuse box.
Gear Position Switch
A gear position switch is located on the automatic gearbox and is used to inform the BCU of the gear selector lever position. The BCU has four sensing inputs from the gear position switch contacts W, X, Y, Z, which are used to determine the gearbox drive status at any particular instance. The BCU gives an output corresponding to the gearbox status derived from the gear position switch inputs. The logic states defining the gear selector positions are listed in the table below, where Z1, Z2, Z3 and Z4 represent intermediate states which exist as the selector lever position is changed:
The existence of an intermediate state causes a fault code to be detected by the BCU. To reduce the chances of the fault condition occurring while changing selector lever position, the inputs are debounced and only considered valid when they have existed for at least 33 ms.
Transmission neutral selector
The transmission neutral sensor provides an earth signal to the BCU when the transfer box is in neutral. The earth signal causes the BCU to operate an audible warning when the transfer box is in neutral with the ignition switched on.
Self Levelling Suspension and ABS
The BCU communicates with the SLABS ECU for several functions:
^ An output is provided from the SLABS ECU to the BCU to provide the logic conditions for issuing the SLS audible warning.
^ The BCU receives an input from the SLABS ECU relating to the raise/lower command from the remote handset.
Hill Descent Control
The BCU provides an output signal to the SLABS ECU for automatic transmission in neutral for HDC control. The BCU checks the status of the ignition and 'gearbox state' inputs and provides a 'Neutral selected' output. If the ignition is on and 'gearbox state' is Neutral, the 'Neutral selected' output is on, otherwise 'Neutral selected' is off.
Heated Screens
The Heated Front Screen (HFS) is fitted for some market destinations and is operated from a non-latching switch located on the instrument pack cowl. The BCU will only allow the heated front screen to operate when the engine is running and controls the time-out period for switching the circuit off.
The heated front screen operation can also be controlled from the Automatic Temperature Control (ATC) ECU on vehicles fitted with air conditioning.
The heated rear window will only function when the engine is running, and is operated by a non-latching switch on the instrument pack cowl. The heated rear window can also be operated by the ATC ECU on vehicles fitted with air conditioning.
Interior Courtesy Lamps
The BCU controls the operation of the interior courtesy lamps. The courtesy lamps are situated in the front, mid and rear areas of the headlining.
Fuel Flap Actuator
The BCU provides an earth path to the fuel flap release solenoid to allow the fuel filler flap to be opened. This is only allowed if the alarm system is not set and all other conditions have been satisfied. The fuel flap release switch is located in the fascia switch pack and it receives a voltage supply from the passenger compartment fuse box.
Audible Warnings
The BCU can request the instrument pack to generate an audible warning in response to conditions it has detected and which need to be drawn to the driver's attention. One of six different audible warnings can be requested by the BCU.
