Seat Heater Switches

SEATS

76-5-8

DESCRIPTION AND OPERATION

Seat Heating

Description
The heated seat system is fitted to both the driver's and front passenger's seat and selected by individual push-button 
switches, each with an integrated LED display.

Location of Seat Heating Controls

The electrical sub-system consists of the following components:

l

Seat heater switches

l

Seat heater elements (squab/backrest)

l

Temperature control unit

l

Temperature sensor.

Temperature Control Unit
Feedback of the seat temperature is via a Negative Temperature Coefficient (NTC) sensor within the seat cushion. 
The resistance of this sensor changes with the temperature of the seat cushion allowing the temperature control unit 
to raise or lower the voltage to the seat heater elements to raise or lower their temperature.

An ignition feed is supplied via the heater switch. The temperature sensor supplies an input. Output is a supply to the 
cushion heater element and an earth.

 Seat Heater Switches
The two push-button switches, fitted in the central console, each have an integrated functional display and, to assist 
system fault diagnosis, a self-test function. The display indicates the heating level selected and, when used for fault 
diagnosis, the fault code.

Both LEDs OFF – No heating

Two LEDs ON – High level heating (44

°

C)

One LED ON – Low level heating (39

°

C)

The seat heater switches supply an ignition feed to the temperature control unit. When a seat heater switch is 
operated, current flows to the seat heater elements causing them to heat the seat.

The switch regulates the level of seat heating if its internal temperature starts to rise above 85

°

C. Initially the level of 

seat heating is reduced to 88 % then progressively reduced until, if the internal temperature exceeds 95

°

C, the system 

shuts-down.

M76 4553