Retrofit Heated Driver and Passenger seats

[asdf4fdsa]

Thanks to this forum, and feeling confident from finishing the ACC retrofit, now tackling the next retrofit. Looking to retrofit OEM controls with aftermarket heat pads.

I've got a weirdly optioned LCI X5 35i 7-seater that does not have heated seats, I'm assuming because of S823 Hot-climate version option. It does have S456-Comfort seat with memory, and S488-Lumbar support, driver and passenger. I think 20-way adjustable. Not active seats, so more cushion and less wires.

I took a look at the schematics before the Newtis takedown, and here's what's needed
1. Retrofit the IHKA
2. Install the 4 heat pads between the leather and the occupancy sensor and plug in to the seat's controller (3 wires)

The car does have an SMFA and SMBF, with 30A fuses at F101 and F102 respectively.

Fitting the heating pads would not be too difficult, I've taken the seats apart. One problem is the type of thermistor to use, since I cannot seem to find separate heat pads specifically for the E70 seats. If somebody can profile their thermistor through the 3 heat settings, or if I can buy one somewhere.

Once hooked up, code CAS and FRM with $494, then program and code IHKA to car.

The IHKA should simply send a can message to the SMFA or SMBF via the JBB, and the heated seats should come on.

Am I missing anything else?

[asdf4fdsa]

Update: Found the connector and pins to connect up to the SMFA(A187) and SMBF(A186):
2x 61136901842 connector housing for 22004 and 22014
2x 61136901832 connector housing for 22005 and 22015
8x 61138364834 high current connector clip
4x 61131393724 low current connector clip

I've also found the thermistor set points in ISTAd, as part of the heated seat test. This will help with locating the right thermistors to use.

Setpoints:
12.7K 15C
10.0K 20C
8.0K 25C
6.4K 30C
5.2K 35C
4.2K 40C
3.4K 45C

Still using ISTAd I found the SMFA and SMBF has a seat heater reading and enable the heat pads. I can read the temperature from my resistor, but the pads do not heat up. I do hear a click, and there is a 12V output at the high current pins. Still looking into this. It could be IHKA not sending the right signal yet to throttle the ground somewhere, but have not found a way to check that.

I've found an IHKA High with the heated seat function, installed and coded. ISTAp did not require programming. I checked NCSexpert and shows heated seat function active. I also couldn't find anything in the JBB pertaining to heated seats. I've updated FA with the $494 option. The problem is when I click either heated seat buttons, none of the three LEDs light up.

[asdf4fdsa]

Finally got the buttons to light up! The SMFA and SMBF needed to be programmed. Once complete, the 3 LEDs on the IHKA buttons lit up when pressed.

As a note, the potentiometer hooked up to the heating pad allowed the pad to heat up only at certain ranges. This means if the thermistor ever has a break in the wire or shorts out the heaters will not come on.

The driver's side has no circuitry hooked up, and hitting the button, the LED lights will come on, then turn off after a second. Relay under the seat will also click accordingly. The circuit must be looking for the thermistor feedback.

Now after activating each of the buttons, ISTAd will show errors for the pads (since 3 of them are not hooked up yet) for all but 1, the passenger bottom cushion with the pot hooked up.

Waiting for the thermistors to arrive now.

[asdf4fdsa]

Fully profiled the 3 settings of the heated seat buttons:
Stage: 12V temp -> 0V temp -> Off (LED off)
Stage3 (3 LED lit): 40C -> 48C -> 90C
Position2 (2 LED lit): 35C -> 44C -> 90C
Position1 (1 LED lit): 32C -> 40C -> 90C

Looks like I'll need to find an 8K NTC Thermistor for this project to be accurate on the heated pads. BTW, I'm just using cheap carbon fiber heated seat pads off Ebay.

BMW design issue: The system does not seem to care if the thermistor is disconnected, an open circuit indicates cold (-40C), so the system continues to supply power to the heat pads. In case of an overrun or a fire and the thermistor line is broken, the system would continue to heat. BMW should have used a PTC thermistor, thereby a disconnection of the thermistor would cause the power to shutdown to the heated pads, reducing risk of burns/fire.

Thanks BMW: The system as designed allows us to operate the heated seats without a connected thermistor, just turn it off if it gets too hot! I'll hook it up this way until the thermistors arrive.

[asdf4fdsa]

Was finally able to remove the leather off the cushion, and left the OC3 pad still on the cushion. Loads of hog nose rings to remove and replace. It turns out the leather is integrated with a thick fabric pad. Although there seems to be pockets between the leather and this pad, I opted to put the heating mats between this thick fabric pad and the OC3. Hopefully the OC3 does not burn out prematurely from high heat.

Still leaving the thermistors out until they arrive. I think 10k thermistors will work, the system will just have a 5C offset.

[Gtflash]

Did you ever finish this project?