$28 seat heat pad replacement DIY

[jeepo23]

Just getting to this now.. I have the heated pads and I started taking the seat apart to discover..

That on the non-sport seats, the 2 seat centres that span across the bottom cushion are actually attached to the leather. So you can't just slide a heat pad under the insulation due to this part that runs across so it's like the bottom part is 3 separate sections.

What about putting the heat pad between the cushion and the insulation itself? That's the only way I can get it to span the entire bottom area..

[Turbo_Bimmer]

Originally Posted by jeepo23

Just getting to this now.. I have the heated pads and I started taking the seat apart to discover..

That on the non-sport seats, the 2 seat centres that span across the bottom cushion are actually attached to the leather. So you can't just slide a heat pad under the insulation due to this part that runs across so it's like the bottom part is 3 separate sections.

What about putting the heat pad between the cushion and the insulation itself? That's the only way I can get it to span the entire bottom area..

Hello, I don't see a problem there. It will only be a bit longer to heat but it should be ok. I know someone with a X3 that installed it like this and it works well also.

My X doesn't have the sport seats, but the comfort seats and it was not in 3 sections. Maybe it depends of the years. What year is yours? Mine is a 2005.

[jeepo23]

Originally Posted by Turbo_Bimmer

Hello, I don't see a problem there. It will only be a bit longer to heat but it should be ok. I know someone with a X3 that installed it like this and it works well also.

My X doesn't have the sport seats, but the comfort seats and it was not in 3 sections. Maybe it depends of the years. What year is yours? Mine is a 2005.

Hmm... I got a 2002, but its a 330XI.

I did try it this way, plugged everything in and as soon as I turn on the seat heaters in the car they would turn off.. like instantly.

My pad has 3 wires (pad +, pad -, and temp sensor +).

I took the pad + to the green/voilet, pad - to brown. Didn't connect the temp sensor wire at all, and left the BMW gray wire intact also as that it's temperature sensor.

After trying to figure this out I got too pissed off and put everything back together.. the way it was and now my heated seats work again in the car.. LOL. Not sure if wiggling the wires did something or lifting up the seat cushion and looking around in there but now they magically work again.

[jeepo23]

Damn car... the seat stopped working again... Right when it starts getting colder here in Canada.

[Turbo_Bimmer]

Originally Posted by jeepo23

Damn car... the seat stopped working again... Right when it starts getting colder here in Canada.

jeepo23, your connections seem fine, unless a 330xi has different color code?
It was working a couple of months ago and now it stopped?
Maybe there is a bad contact in the heat sensor. Try to measure the resistance of the grey wire to ground (brown wire). Disconnect the connector from the harness first. You should read something around 1K or around 10K. What is not normal is either a short circuit or open circuit.
Is your passenger seat working normally?

[jeepo23]

Originally Posted by Turbo_Bimmer

jeepo23, your connections seem fine, unless a 330xi has different color code?
It was working a couple of months ago and now it stopped?
Maybe there is a bad contact in the heat sensor. Try to measure the resistance of the grey wire to ground (brown wire). Disconnect the connector from the harness first. You should read something around 1K or around 10K. What is not normal is either a short circuit or open circuit.
Is your passenger seat working normally?

Thanks for the help.
The colors are the exact same under the seat as yours.
Basically it seems to work sometimes depending the way you sit.. so clearly its a short somewhere.
If it is a bad contact with the heat sensor - how can one fix this?

And yes, the passenger seat works 100% fine - this is using the OEM setup not this aftermarket pad install idea.

[Turbo_Bimmer]

If it is the sensor, from the measurement I took if my memory is good, it seemed to be in the several Kohm value (7-10K). If it is the case (can verify with the working seat), that means it is a thermistor. Those can be bought for cheap in electronic stores locally or online at places like Digikey.ca.
Here is an example:
B57871S123F EPCOS Inc | 495-3037-ND | DigiKey

If you think it is the sensor, you have to determine what is its value at 25°C or close (that's the way they are rated) and also, see if its resistance increases or decreases as temperature goes up. PTC or NTC type. You can measure the resistance of the sensor when the seat is at room temperature, then, reconnect it, heat the seat, disconnect and measure again the resistance to see if it increased or decreased.
If you buy only the thermistor like in the link above, you will have to solder wires to it and of course install it in a different layer than the heat pad.

Something you could try before all this, is to connect a meter (in ohms) to the sensor vs ground (brown wire) and sit on the seat and move around to see if the reading is stable and not OL or short.

[jeepo23]

Turbo_Bimmer, thanks for the info.

Due to the temperatures out there it's a bit hard to measure the resistances currently yet alone pull the whole seat out of the car.

I took the aftermarket pad I purchased off eBay and measured it's resistance and it reads 10k on the dot.

If this is the case, no matter what my issue is - broken heating grid or sensor broken shouldn't I be able to just take this pad and install it under my seat and connect these 3 wires from it to the OEM system and off I go?

[Turbo_Bimmer]

Well, it depends if its resistance rises or lowers with temperature increase. Also, if the BMW sensor is a 6K for example, it may heat more or heat less depending of the difference.
You can try it. It will either control well, or won't heat at all. Just connect the sensor of the new mat to the grey and the brown wires of the BMW and disconnect the grey wire going to the BMW mat.
Doing remote diagnostic is not easy. Please use this information as suggestions and at your own risk, considering I've done that on a X5 and not a 330.

[jeepo23]

Originally Posted by Turbo_Bimmer

Well, it depends if its resistance rises or lowers with temperature increase. Also, if the BMW sensor is a 6K for example, it may heat more or heat less depending of the difference.
You can try it. It will either control well, or won't heat at all. Just connect the sensor of the new mat to the grey and the brown wires of the BMW and disconnect the grey wire going to the BMW mat.
Doing remote diagnostic is not easy. Please use this information as suggestions and at your own risk, considering I've done that on a X5 and not a 330.

Turbo_Bimmer,

I've had some time to actually check some things out. Basically these are my findings.

The heat pad I have that I purchased off ebay reads 10k when OFF, I connected the heat pad to a 12V car battery to see what happens to the resistance between the sensor wire and ground of this ebay heat pad and it starts to drop.. So that confirmed to me that the heat pad temp sensor on this pad does in fact drop as it gets warmer.

Now the BMW heated seat.. The past couple of days were actually very mild around here where the temperature were -1C and even +3C, I tried my heated seat just out of fun the other night and it worked. The light actually stayed on, moving around the seat etc didn't trigger it off so I'm starting to believe that it's not a short issue but instead the actual temperature sensor is faulty in the seat.

Because it appears that the thing will work if it's warmer outside and not -20C. This morning was already a lot colder and it tried the heated seat and it didn't work light just flickers off.

I think my best bet would be to swap the stock temp sensor with the one from this ebay pad I purchased. Now my question, is this even doable or are the sensors sewn into something and impossible to get at?