Heated seat low voltage

[JosephJ]

Hello! As it's getting colder, I thought I'd try and fix my heated seats. Upon removal, I've found that the wiring in the seats is fine and the issue appears to be on the cars end. I've checked the voltage supply to the switches and they are showing 12+ volts. At the connection under the seat, I'm getting 5.45 volts off pins 1 and 2 regardless if the switch is on or off.

Can the switches fail this way? They still light up when pressed and the fuse is all okay. I've had a look at the operations manual and can't find a huge amount of information.

Many thanks
Joe

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[SD1too]

Originally Posted by JosephJ

At the connection under the seat, I'm getting 5.45 volts off pins 1 and 2 regardless if the switch is on or off.

How are you measuring this Joe?

The seat elements are supplied with +12v directly. The switches connect the elements to earth.

Under the seat, put your red meter probe on pin 2 orange/white to measure the input to the seat element.
With the switch button pressed you should see 0v on pin 1 yellow.
In both cases your black meter probe must be on a good earth.

You won't feel the heat using your hand, you'll have to sit on the seat.
The engine will probably need to be running as well (check your handbook).

Simon

[JosephJ]

Originally Posted by SD1too

How are you measuring this Joe?

The seat elements are supplied with +12v directly. The switches connect the elements to earth.

Under the seat, put your red meter probe on pin 2 orange/white to measure the input to the seat element.
With the switch button pressed you should see 0v on pin 1 yellow.
In both cases your black meter probe must be on a good earth.

You won't feel the heat using your hand, you'll have to sit on the seat.
The engine will probably need to be running as well (check your handbook).

Simon

Thank you Simon.

For the 5.45 volts, I was using the bolt holes for the seats as earth (as I had them removed). Luckily the threads are spotless. To test, I had my red lead on pin 1 (yellow) and the black in the bolt hole. The second reading was done exactly the same but with the red lead in pin 2 (orange/white).

When I got the reading for 12 volts, I had my multimeter red lead on the orange white wire and the black on the black wire. This was on the connection to the heated seat switch in the center console.

I shall have a look again tomorrow as I only had the ignition on, not the engine running.

Joe


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[SD1too]

Originally Posted by JosephJ

... I had my multimeter red lead on the orange white wire and the black on the black wire. This was on the connection to the heated seat switch in the centre console.

The heated seat switch black wire is a much more reliable earthing point than the bolt holes. I'd recommend that you use the black wire for all your measurements.

Simon

[JosephJ]

Originally Posted by SD1too

The heated seat switch black wire is a much more reliable earthing point than the bolt holes. I'd recommend that you use the black wire for all your measurements.

Simon

I shall do. Just to confirm, the switch just grants access to ground for the heated seat circuit? I'm assuming that with the button pressed and engine running I should get ground to the under seat connection?

Joe

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[SD1too]

Originally Posted by JosephJ

Just to confirm, the switch just grants access to ground for the heated seat circuit?

Yes it does, but does it include timer circuitry as well? Maybe I'm thinking of the HRW.

Simon

[JosephJ]

Originally Posted by SD1too

Yes it does, but does it include timer circuitry as well? Maybe I'm thinking of the HRW.

Simon

I believe it does! Well within the switch. Just tested the circuitry with the car running and all is well. I do have continuity at the seat too and visually inspected the elements when I changed the covers. I know the seats are a little weak so I may look into better heat pads or thermostats in the future

Joe

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[SD1too]

Originally Posted by JosephJ

Just tested the circuitry with the car running and all is well.

Excellent!

Simon

[JosephJ]

Update time!

So the seats now appear to work but are extremely weak. Is this a normal feature of our lovely cars? If so a thermostat upgrade may be needed. Just need to sort out all the interior rattles now!

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[The Rovering Member]

They get warm but turn off early either by temperature or timer. They're not brilliant but you notice the difference especially on cold leather. The cloth seats do warm up more efficiently AFAIK.