1999 LAND ROVER DISCOVERY ignition

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 76-5-11
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.

SUNROOF
76-6-6 DESCRIPTION AND OPERATION
Front sunroof switch
The front sunroof switch is located in the roof console above the windscreen in front of the front sunroof. It controls
the front sunroof motor via the sunroof ECU.
The front sunroof switch supplies an earth signal to the sunroof ECU. The pin at the ECU that receives the earth
signal determines whether ECU causes the sunroof to open or close.
TestBook cannot monitor the state of the front sunroof switch.
The following table lists the values which can be measured at the listed ECU pins when the conditions outlined are
met:
Signal values (connector connected)
Connector/Pin
No.Condition Resistance, ohms
C0784-2 Ignition in position II, front sunroof switch released > 10,000
C0784-2 Ignition in position II, front sunroof switch open < 0.5
C0785-7 Ignition in position II, front sunroof switch released > 10,000
C0785-7 Ignition in position II, front sunroof switch closed < 0.5

SUNROOF
DESCRIPTION AND OPERATION 76-6-7
Front sunroof motor and microswitch
The front sunroof motor is located within the front sunroof assembly. The sunroof ECU controls the front sunroof
motor.
The sunroof ECU determines the direction the sunroof motor runs. A battery signal to one side of the motor and an
earth to the other side of the motor causes the motor to turn in one direction, reversing the polarity through the same
pins causes the motor to turn in the opposite direction.
The following table lists the values which can be measured at the listed ECU pins when the conditions outlined are
met:
Signal values (connector connected)
Connector/Pin
No.Condition Voltage Resistance, ohms
C0785-5 Ignition in position II, rear of front sunroof switch
pressed+voltage to C0785-
5
C0785-1 Ignition in position II, front of front sunroof switch
pressed+voltage to C0785-
1< 0.5
C0784-8 Ignition in position II, sunroof fully closed +V Batt
C0784-8 Ignition in position II, sunroof not closed > 10,0000

SUNROOF
76-6-8 DESCRIPTION AND OPERATION
Rear sunroof - front switch
The rear sunroof front switch is located in the roof console above the windscreen in front of the front sunroof. It
controls the rear sunroof motor via the sunroof ECU.
The rear sunroof front switch supplies an earth signal to the sunroof ECU. The pin at the ECU that receives the earth
signal determines whether ECU causes the sunroof to open or close.
TestBook cannot monitor the state of the rear sunroof front switch.
The following table lists the values which can be measured at the listed ECU pins when the conditions outlined are
met:
Signal values (connector connected)
Connector/Pin
No.Condition Ohms
C0784-7 Ignition in position II, rear sunroof front switch released > 10,000
C0784-7 Ignition in position II, rear sunroof front switch open < 0.5
C0785-8 Ignition in position II, rear sunroof front switch released > 10,000
C0785-8 Ignition in position II, rear sunroof front switch closed < 0.5

SUNROOF
DESCRIPTION AND OPERATION 76-6-9
Rear sunroof isolation switch
The rear sunroof isolation switch is located in the roof console above the windscreen in front of the front sunroof. It
prevents the rear sunroof rear switch from operating the rear sunroof.
The rear sunroof isolation switch is in the earth path between the rear sunroof rear switch and the sunroof ECU.
Operating the rear sunroof isolation switch opens the circuit and prevents the rear sunroof rear switch from operating
the rear sunroof.
TestBook cannot monitor the state of the rear sunroof isolation switch.
The following table lists the values which can be measured at the listed ECU pins when the conditions outlined are
met:
Signal values (connector connected)
Connector/Pin
No.Condition Resistance, ohms
C0784-6 Ignition in position II, rear sunroof rear switch open, rear
sunroof isolation switch pressed> 10,000
C0784-6 Ignition in position II, rear sunroof rear switch open, rear
sunroof isolation switch released< 0.5
C0785-9 Ignition in position II, rear sunroof rear switch closed, rear
sunroof isolation switch pressed> 10,000
C0785-9 Ignition in position II, rear sunroof rear switch closed, rear
sunroof isolation switch released< 0.5

SUNROOF
76-6-10 DESCRIPTION AND OPERATION
Rear sunroof rear switch
The rear sunroof rear switch is located in the roof console in front of the rear sunroof. It controls the rear sunroof
motor via the sunroof ECU.
The rear sunroof front switch supplies an earth signal through the rear sunroof isolation switch to the sunroof ECU.
The pin at the ECU that receives the earth signal determines whether ECU causes the sunroof to open or close.
TestBook cannot monitor the state of the rear sunroof rear switch.
The following table lists the values which can be measured at the listed ECU pins when the conditions outlined are
met:
Signal values (connector connected)
Connector/Pin
No.Condition Resistance, ohms
C0784-6 Ignition in position II, rear sunroof isolation switch closed, rear
sunroof rear switch released> 10,000
C0784-6 Ignition in position II, rear sunroof isolation switch closed, rear
sunroof front switch open< 0.5
C0785-9 Ignition in position II, rear sunroof isolation switch closed, rear
sunroof front switch released> 10,000
C0785-9 Ignition in position II, rear sunroof isolation switch closed, rear
sunroof front switch closed< 0.5