Body control unit (Headlamps): Description and operation

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. INSTRUMENTS, DESCRIPTION AND OPERATION, Description. l The instrument pack provides the BCU and IDM with details of vehicle speed. l Signals are provided from the IDM to the instrument pack and BCU when the direction indicator lamps are active. l For certain markets, the BCU provides a signal to the instrument pack for indicating when the transfer box is in neutral. l 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. l 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. l 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: l When the brake pedal is pressed, a low voltage brake lamp signal is sent via the BCU to the cruise control ECU. l 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. l A voltage supply is fed from the BCU to the cruise control SET+ switch. l 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. ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description. ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - cruise control.

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. AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.