LAND ROVER DISCOVERY 1999 Workshop Manual

SEATS
76-5-4 DESCRIPTION AND OPERATION
Description - electric seats
General
All markets use the same electric seat system. Electically operated lumbar support is optional. The system consists
of an electrical sub-system and a mechanical sub-system.
The electrical sub-system consists of the following components:
lBCU.
lSeat power relays.
lSeat switch packs.
lSeat fore/ aft motors.
lSeat cushion front up/ down motors.
lSeat cushion rear up/ down motors.
lSeat squab motor.
lLumbar pump.
lLumbar deflate solenoid.
The mechanical sub-system consist of the following components:
lGear wheels.
lRack and pinion assemblies.
Seat power relay
Located beneath the seat, the seat power relay supplies battery voltage to the satellite fuse box. Operation of the
relays is controlled by the BCU.
Voltage to the seat power relays is from fuse 5 in the engine compartment fuse box. The BCU controls the earth for
the relay coils. Operating the seat power relays provides voltage to the satellite fuse box under each seat.
Satellite fuse box
Located beneath the seat, the satellite fuse box provides circuit protection for the wiring to the seat switches and
motors. It also protects the lumbar inflate and deflate circuits.
The seat power relay provides voltage directly to the 40A fuse in the satellite fuse box. Voltage from this fuse feeds
the seat switch pack. The 3A fuses in the satellite fuse box protect the wiring to the lumbar pump and lumbar deflate
solenoid. Voltage to the 3A fuses comes from the seat switch pack.

SEATS
DESCRIPTION AND OPERATION 76-5-5
Seat switch pack
Each seat switch pack contains two switches representing the seat cushion and the seat squab. The switches provide
the following adjustments:
lSeat fore/ aft.
lCushion front up/ down.
lCushion rear up/ down.
lSquab fore/ aft.
lLumbar inflate.
lLumbar deflate.
The voltage supply to the seat switch pack is from the 40A fuse in the satellite fuse box. A pair of switches controls
the operation of each seat motor, the lumbar pump and the lumbar deflate relay.

SEATS
76-5-6 DESCRIPTION AND OPERATION
Seat fore/ aft motor
The seat fore/ aft motor is a permanent magnet motor coupled to a rack and pinion assembly. Should the motor seize
or stick for 6 seconds or more, an internal thermal cut out switch will trip to remove voltage from the motor. Reset
time for the switch is 35 seconds.
Two pins within the seat switch pack control the seat fore/ aft motor. Both pins are normally earthed. Operating the
backward switch applies voltage to that pin while the other pin remains earthed. Operating the forward switch reverses
power and earth to the motor allowing the motor to run in the opposite direction.
Seat cushion front up/ down motor
The seat cushion front up/ down motor is a permanent magnet motor coupled to a rack and pinion assembly. Should
the motor seize or stick for 6 seconds or more an internal thermal cut out switch will trip to remove voltage from the
motor. Reset time for the switch is 35 seconds.
Two pins within the seat switch pack control the seat cushion front up/ down motor. Both pins are normally earthed.
Operating the up switch applies voltage to that pin while the other pin remains earthed. Operating the down switch
reverses power and earth to the motor allowing the motor to run in the opposite direction.
Seat cushion rear up/ down motor
The seat cushion rear up/ down motor is a permanent magnet motor coupled to a rack and pinion assembly. Should
the motor seize or stick for 6 seconds or more, an internal thermal cut out switch will trip to remove voltage from the
motor. Reset time for the switch is 35 seconds.
Two pins within the seat switch pack control the seat cushion rear up/ down motor. Both pins are normally earthed.
Operating the up switch applies voltage to that pin while the other pin remains earthed. Operating the down switch
reverses power and earth to the motor allowing the motor to run in the opposite direction.
Seat squab fore/ aft motor
The squab fore/ aft motor is a permanent magnet motor coupled to a rotary rack and pinion assembly. Should the
motor seize or stick for 6 seconds or more, an internal thermal cut out switch will trip to remove voltage from the motor.
Reset time for the switch is 35 seconds.
Two pins within the seat switch pack control the squab fore/ aft motor. Both pins are normally earthed. Operating the
fore switch applies voltage to that pin while the other pin remains earthed. Operating the aft switch reverses power
and earth to the motor allowing the motor to run in the opposite direction.

SEATS
DESCRIPTION AND OPERATION 76-5-7
Lumbar pump
The lumbar pump inflates a bladder in the squab which provides extra support for the seat occupant. With no load on
the seat it takes approximately 10 seconds to completely inflate the bladder. With a load of 25 kg (55 lb) it takes
approximately 15 seconds to inflate the bladder. A pressure cut off switch in the system will operate at 0.12 to 1.93
bar (1.8 to 28 lbf.in
2). If a problem occurs with the lumbar bladder, e.g. a rupture, the whole lumbar system must be
replaced. The components are not serviceable.
Power comes from the seat switch pack through a 3A fuse in the satellite fuse box. The lumbar pump and the lumbar
deflate solenoid share an earth.
Lumbar deflate solenoid
The lumbar deflate solenoid vents the lumbar bladder to atmosphere to allow air to evacuate the bladder. The average
time to evacuate the bladder with a load of 25 kg (55 lb) is 9 seconds.
Power comes from the seat switch pack through a 3A fuse in the satellite fuse box. The lumbar deflate solenoid and
the lumbar pump share an earth.

SEATS
76-5-8 DESCRIPTION AND OPERATION
Operation - electric seats
Seat power relay enable line
The BCU provides the seat power relays with an earth supply to the relay coil that enables the relay operation. When
this seat power relay enable line is active, the seat power relay energises allowing seat operation.
In order for the seat power relay to be active the BCU must detect either of the following condition options:
lIgnition switch in position II.
lIgnition switch in position II or driver's door within 45 seconds of opening.
Seat fore/ aft movement
When the cushion switch is operated and the seat power relay enable line is operating, power and earth are supplied
to the motor in the seat, allowing the seat to move forward or backward depending on switch position. The motor
drives a gear wheel along a gear rack connected to the seat base. Sliding the cushion switch forward causes the motor
to drive the seat forward. Sliding the cushion switch rearward reverses polarity of the voltage at the seat motor, driving
the seat rearward.
Seat cushion front up/ down movement
When the cushion switch is operated and the seat power relay enable line is operating, power and earth are supplied
to the motor in the seat, allowing the front of the seat cushion to move upward or downward depending on switch
position. The motor drives a gear wheel along a gear rack connected to the seat base. Sliding the front of the cushion
switch upward causes the motor to drive the seat upward. Sliding the front of the cushion switch downward reverses
polarity of the voltage at the seat motor driving the seat downward.
Seat cushion rear up/ down movement
When the cushion switch is operated and the seat power relay enable line is operating, power and earth are supplied
to the motor in the seat, allowing the seat to move upwards or downwards depending on switch position. The motor
drives a gear wheel along a gear rack connected to the seat base. Sliding the rear of the cushion switch upward
causes the motor to drive the seat upward. Sliding the rear of the cushion switch downward reverses polarity of the
voltage at the seat motor driving the seat downward.
Squab fore/ aft movement
When the squab switch is operated and the seat power relay enable line is operating, power and earth is supplied to
the motor in the squab, allowing the squab to move forward or backward depending on switch position. The motor
drives a gear wheel along a rotary gear rack connected to the squab. Sliding the squab switch forward causes the
motor to drive the squab forward. Sliding the squab switch rearward reverses polarity of the voltage at the seat motor
driving the squab rearward.
Lumbar inflate/ deflate
Sliding the squab switch upwards when the seat power relay enable line is operating applies voltage to the lumbar
pump. The lumbar pump inflates the lumbar bladder, increasing lumbar support. The lumbar pump and the normally
closed lumbar deflate solenoid hold the air in the bladder. Sliding the squab switch downwards applies voltage to the
deflate solenoid, venting the air in the lumbar bladder to atmosphere, decreasing lumbar support.
Diagnostics
TestBook can only verify that the seat power relay line is enabled. It cannot determine the status of the system or any
of the components.

SEATS
DESCRIPTION AND OPERATION 76-5-9
DESCRIPTION AND OPERAT ION
Heated seat component location
1Heater module2Seat heater switches

SEATS
76-5-10 DESCRIPTION AND OPERATION
Heated seat block diagram (electric
seats)
1Passenger compartment fuse box
2Left seat heater switch
3Left seat heater module
4Left seat cushion heater element
5Left seat squab heater element 6Right seat heater switch
7Right seat heater module
8Right seat cushion heater element
9Right seat squab heater element

SEATS
DESCRIPTION AND OPERATION 76-5-11
Description - heated seats
Heated seats
The heated seat system is available on both manual seats and electric seats. The electrical sub-system consists of
the following components:
lSeat heater switches.
lSeat heater elements.
lTemperature control unit (if electric seats are fitted).
lTemperature sensor (if electric seats are fitted).
lThermostat (if manual seats are fitted).
Seat heater switches
The seat heater switches supply an ignition feed to either the temperature control unit (vehicles with electric seats) or
directly to the seat heater elements (vehicles with manual seats). When a seat heater switch is operated, current flows
to the seat heater elements causing them to heat the seat.
The ignition feed comes from fuse 15 in the passenger compartment fuse box.
Seat heater elements
The seat heater elements are located in the seat cushion and squab. The cushion and squab heater elements are
wired in series. Total power consumption at 13.5 volts is approximately 115 Watts.
The cushion heater element has an input feed from the temperature control unit or heater switch and an output to the
squab heater element, which outputs to earth.

SEATS
76-5-12 DESCRIPTION AND OPERATION
Temperature control unit
The temperature control unit is only fitted to vehicles with electric seats. Feed back of the seat temperature is via a
Negative Temperature Coefficient (NTC) sensor within the seat cushion. Resistance of this sensor changes with the
temperature of the seat cushion allowing the temperature control unit to lower or raise the voltage to the seat heater
elements to raise or lower their temperature.
An ignition feed is supplied via the seat heater switch. The temperature sensor supplies an input. Output is a supply
to the cushion heater element and an earth.
Thermostat
On vehicles with non electric seats, the temperature is controlled by a thermostat located in the seat cushion. The
thermostat interrupts the power supply when it reaches a pre-determined temperature.

SEATS
DESCRIPTION AND OPERATION 76-5-13
Operation - heated seats
When the seat heater switch is operated, power is supplied to the heater elements in the seat, causing the seat to
heat up. On vehicles fitted with non electric seats, the thermostat switches the power supply to the heater elements
on and off. On vehicles fitted with electric seats, the temperature control unit senses seat temperature via the sensor
in the cushion and regulates voltage to the seat heater elements to maintain a constant temperature.
On both electric and non electric seats, the heater elements increase and then maintain the seat at a temperature
between 26 and 36 °C (79 and 97 °F).