Land Rover Discovery: Seat Heater Mat
Faults -Diagnostic Guidance
- Seat Heater Sensor Faults - Each seat has two heating elements: one in
the base (seat cushion), and one in the back (squab). There is only one
sensor, which is located in the base. This sensor controls both heating
elements. If there is a fault with the sensor signal, neither element will
operate. If the signal fault is traced to the sensor itself (in the
base/seat
cushion mat), there is no need to replace the back/squab heater mat.
- Diagnosis Of Seat Heater Elements Using Resistance Measurements -
The back/squab heater mat consists of a heating element, the base/seat
cushion heater mat consists of a heating element with a sensor. Most
faults can be confirmed by simple electrical resistance measurements,
using the values listed below. It is possible that the sensor could develop
a fault causing it to exhibit either higher resistance (resulting in the
seat
heaters operating at too high a temperature), or lower resistance
(resulting in the seat heaters operating at too low a temperature or not at
all), but these kinds of faults are uncommon. The maximum resistance of
the seat elements are only about 1 ohm each under normal operation, so
it is difficult to take an exact reading with a standard multimeter.
However,
the most likely cause of failure is breaks in a number of the heater
element wires, which causes both a significant loss of heating and a
corresponding significant increase in resistance. In this situation, both
(seat cushion AND squab) elements produce less heat, but contrary to
expectation, it is the undamaged element which will show the greatest
loss of heating. Given this, suspected seat heater element failures should
always be confirmed by electrical resistance tests before replacement. Do
not replace components based only on temperature performance.
- Simultaneous Failure of Both Seat Heater Mats Is Unlikely - The
base/seat cushion and back/squab seat heater elements connect to the
automatic temperature control module, but the control module only acts
as a splice box and the elements are electrically wired in series (each
drawing proportion of battery voltage). The only way for one element to
operate while the other is faulty is if one is the elements has a
short-circuit
fault. Under normal circumstances, where short-circuit faults are present
these will be detected by the automatic temperature control module
which will switch off both elements. Similarly, if the sensor (in the
base/seat cushion element) is faulty, the automatic temperature control
module will not apply voltage to the elements and, if one element is
open-circuit, then no voltage can be supplied to the other element. Given
this, while it may often be the case that both elements cease to operate,
it is extremely unlikely that both heater mats are faulty. Consequently, if
a
fault is confirmed with one of the seat heater mats, do not also replace
the other.
- Seat Heater Sensor Open Circuit Faults - Previous investigations have
found the mostly likely failure mode to be associated with the seat heater
sensor (in the base/seat cushion element) developing an open-circuit fault.
This can be measured by disconnecting the 4-way plug from the
automatic temperature control module, and (Test 1) testing the circuit into
the harness; if an open-circuit fault is detected, then test the circuit at
the
connector under the seat (Test 2). If the open-circuit fault is present both
at Test 1 and Test 2, then suspect the seat heater sensor and replace the
base/seat cushion element. If the open circuit fault is detected at Test 1
but NOT at Test 2, then the harness is most likely faulty. It may not be
necessary to check for DTCs (which log in the automatic temperature
control module), but if this is done: B103A-01 = Right Front Seat Heater
Sensor fault; B1038-01 = Left Front Seat Heater Sensor fault.
SEAT HEATER MAT APPLICATION CHART
NOTE:
To ensure an accurate resistance reading, calibrated test equipment
must be used.
PINPOINT TESTS
NOTE:
On full power the seat should be hot to touch
NOTE:
The seat heater power supply cycles on and off dependant on the
seat and cabin temperature and may only switch on for 5 seconds in
30 seconds.
NOTES:
DTC INDEX
For a list of Diagnostic Trouble Codes (DTCs) that could be logged on this
vehicle, please refer to Section 100-00.
READ NEXT:
REMOVAL
WARNINGS:
To avoid accidental deployment and possible personal injury,
the
backup power supply must be depleted before repairing or
replacing any air bag supplemental restraint system (S
REMOVAL
NOTES:
Some variation in the illustrations may occur, but the essential
information is always correct.
Removal steps in this procedure may contain installation details.
LH illustration sh
REMOVAL
NOTES:
Removal steps in this procedure may contain installation details.
Some variation in the illustrations may occur, but the essential
information is always correct.
LH illustration sh
SEE MORE:
REMOVAL
NOTE:
The front bumper mounting is installed in conjunction with:
Front bumper cover
Front bumper
Hood latch panel
Radiator
Windshield washer reservoir
The front bumper mounting is serviced as indicated
Before commencing this procedure make sure that you are aware of
all Health
WARNING:
Before work is carried out, make the air bag supplemental restraint
system safe. For additional information, refer to Standard Workshop
Practices section of workshop manual
NOTES:
The climate controlled seat's (heat and cool) functions will only
operate when the vehicle's engine is runni