BODY CONTROL UNIT: DESCRIPTION AND OPERATION (page 8 of 16)

BODY CONTROL UNIT

86-3-26 DESCRIPTION AND OPERATION

Electric seats
The BCU can be programmed to operate the electric seats according to one of three options:

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Option 1 – no electric seats.

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Option 2 – normal.

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Option 3 – operates with ignition only.

To determine when to provide an output to the passenger and drivers seat enable relay, the BCU checks the condition 
of the following inputs:

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Ignition state.

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Transit mode.

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Driver's door open.

The electrically controlled seats are operated when the ignition switch is in position I or II or for a predetermined period 
when the driver's door is open. If the ignition state is in crank, the seat enable relay is off. If the ignition state is off and 
the driver's door open input is off, the seat enable relay is off. If the ignition state is off and the driver's door open input 
is on and transit mode is on, the seat enable relay output is off.

The power supply to each seat switch pack is powered from a power seat relay located on the underside of each seat 
frame. The feed from the relay is protected by a fuse located in a satellite fuse block located adjacent to the power 
seat relay. The fuse block also contains two additional fuses which are used to protect the feeds to the lumbar pump 
and solenoid.

With the ignition switch in position I or II or the driver's door open, the BCU provides an earth path for the coils of the 
LH and RH power seat relays, energising the relays and closing the contacts. If the driver's door input signal is on for 
longer than 45 seconds with the ignition switched off, the seat enable relay is switched off.

Direction indicators and hazard warning lamps
The BCU supplies reference voltages for the LH and RH indicators. When the direction indicator switch is used to 
select the LH or RH indicator position, an earth path is completed which signals the BCU that a request for direction 
indicator operation has been made. The BCU then communicates this request to the IDM which supplies an earth 
path for the coil of the relevant relay (LH or RH indicator relay). When the relay coil is energised, the relay contacts 
close and a voltage supply is provided via a resistor to the relevant direction indicators. The IDM controls the timing 
of the flash operations by continually removing and restoring the earth path to the direction indicator relay coil.

The BCU checks for the following inputs for performing the logic operations associated with the direction indicator 
lamps:

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Ignition state.

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RH indicators selected.

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LH indicators selected.

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Hazards selected.

l

Inertia switch hazard request.

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One short indicator flash request (anti-theft system arming).

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Two short indicator flash request (superlocking).

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One long indicator flash request (anti-theft system disarming).

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Alarm flashing indicators (anti-theft alarm triggered).

The following outputs are provided by the BCU as a result of the inputs received and the logical operations performed:

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RH indicators enable.

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LH indicators enable.

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Direction indicator left message (link to IDM).

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Direction indicator right message (link to IDM).

Direction indicator lamp failure detection
The BCU uses the following logic inputs to determine if there is a direction indicator bulb failure or if the presence of 
a trailer is detected. The BCU uses the information to decide which output to enable at any particular instance:

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Right direction indicators requested.

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Left direction indicators requested.

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RH indicators current sense.

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LH indicators current sense.