heated seat not working

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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:



Seat heater switches


Seat heater elements (squab/backrest)


Temperature control unit


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.

Seat Heater Elements
The seat heater elements are located in the seat cushion and squab. The cushion and squab heater elements are
wired in parallel. 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.
Operation
When the seat heater switch is initially pressed High level heating is selected, pressing the switch a second time
selects Low level heating and pressing the switch a third time switches the heating off.
The seat heaters are thermostatically controlled and will operate intermittently to maintain a predetermined
temperature. The indicator lights in the switches will remain illuminated until either the heaters are manually turned
off, or the starter switch is turned off.
CAUTION: The seat heaters consume considerable power from the battery. For this reason, they should
ONLY be operated while the engine is running.
When the seat heater switch is operated, power is supplied to the heater elements in the seat, causing the seat to
heat up. 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.

The heater elements increase and then maintain the seat at a temperature of between 37 and 44
°C.

 
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:



Seat heater switches


Seat heater elements (squab/backrest)


Temperature control unit


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.

Seat Heater Elements
The seat heater elements are located in the seat cushion and squab. The cushion and squab heater elements are
wired in parallel. 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.
Operation
When the seat heater switch is initially pressed High level heating is selected, pressing the switch a second time
selects Low level heating and pressing the switch a third time switches the heating off.
The seat heaters are thermostatically controlled and will operate intermittently to maintain a predetermined
temperature. The indicator lights in the switches will remain illuminated until either the heaters are manually turned
off, or the starter switch is turned off.
CAUTION: The seat heaters consume considerable power from the battery. For this reason, they should
ONLY be operated while the engine is running.
When the seat heater switch is operated, power is supplied to the heater elements in the seat, causing the seat to
heat up. 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.

The heater elements increase and then maintain the seat at a temperature of between 37 and 44
°C.


So any idea how to fix a buggered one mate? I'd quite like mine to work lol
 
So where in that write up does it tell you the Fault Diagnosis test??

All it tells you is how it works in normal operation...

No LEDS - OFF
2 LEDS - High
1 LED - Low

I posted the Self Test procedure earlier but here you go (page 505 + 506 of the L322 .pdf)

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​
SEATS​
DESCRIPTION AND OPERATION 76-5-9​
Seat Heater Elements​
The seat heater elements are located in the seat cushion and squab. The cushion and squab heater elements are
wired in parallel. 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.​
Operation​
When the seat heater switch is initially pressed High level heating is selected, pressing the switch a second time
selects Low level heating and pressing the switch a third time switches the heating off.
The seat heaters are thermostatically controlled and will operate intermittently to maintain a predetermined
temperature. The indicator lights in the switches will remain illuminated until either the heaters are manually turned
off, or the starter switch is turned off.​
CAUTION: The seat heaters consume considerable power from the battery. For this reason, they should
ONLY be operated while the engine is running.​
When the seat heater switch is operated, power is supplied to the heater elements in the seat, causing the seat to
heat up. 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.
The heater elements increase and then maintain the seat at a temperature of between 37 and 44​
°C.

Fault Finding​
In the self-test mode the switch indicates faults by displaying a flashing code.
The sequence to select test mode is :​
1​
Press the heating switch with the ignition off

2​
With the switch depressed turn on the ignition switch to Position II

3​
Release the switch, this activates the self-test mode

4​
After 10 seconds the flashing code is displayed.
The flashing code indicates the following faults

l​
1 Flash — Switch overtemperature (T > 95°C)

l​
2 Flashes — Short circuit and/or interruption in the sensor

l​
3 Flashes — Short circuit and/or interruption in the heating elements.
With the switch set to test mode, maximum heating is selected and both lamps are lit. If a fault is identified the heating
is switched off and, after 10 seconds, the left LED switches off , this LED generates the flashing code. If no fault is
detected the LED remains unlit.
To return to the test mode the switch is pressed twice and the sequence starts again. To cancel the test mode the

ignition switch is turned off.
 
Last edited:
I posted the Self Test procedure earlier but here you go (page 505 + 506 of the L322 .pdf)


Fault Finding
In the self-test mode the switch indicates faults by displaying a flashing code.
The sequence to select test mode is :
1


Press the heating switch with the ignition off
2


With the switch depressed turn on the ignition switch to Position II
3


Release the switch, this activates the self-test mode
4


After 10 seconds the flashing code is displayed.
The flashing code indicates the following faults
l


1 Flash — Switch overtemperature (T > 95°C)
l


2 Flashes — Short circuit and/or interruption in the sensor
l


3 Flashes — Short circuit and/or interruption in the heating elements.
With the switch set to test mode, maximum heating is selected and both lamps are lit. If a fault is identified the heating
is switched off and, after 10 seconds, the left LED switches off , this LED generates the flashing code. If no fault is
detected the LED remains unlit.
To return to the test mode the switch is pressed twice and the sequence starts again. To cancel the test mode the
ignition switch is turned off.

Ta - and I do already have RAVE but cheers anyway for the link!:D
 
Last edited:
I 've tried the test regarding my dvrs seat and nothing ...not a blip, guess I'm going to have to just test the wires for an open circuit that are coming out the seat swab ..bloody annoying though ..failing that the heated elements are £50 each base and back and I've got a guy to strip the seat for £50..still more than I'd want to spend but I'm missing it especially in this weather .
 
Fixing the heated seats is a diy repair, normally a break in the base element solder a bit of wire in to bridge the break, the seat base can be taken apart.
 
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