P1: Adding Factory Heated Seats: Hopefully a definitive answer in the future. | SwedeSpeed

I have a 2011 C30 that came without heated seats. Only reason I settled for a car without Heated Seats, HID’s, and Premium audio, is because the HID’s I found an acceptable way to trick the system that’s very low maintenance, and Won’t blow the WMM. Premium Audio I may play with down the road, or may not because I mostly listen to talk radio… The Heated seats, if I have to I will settle for an aftermarket setup.. I would much rather have the OEM Setup working.

There have been a few threads of speculation on if this will work or not, and this means enough to me that I’m willing to spend some money and time figuring it out, and posting results of what does and doesn’t work here. Same should apply to S40/ V50/ C70

Here’s what I have so far: The Heated Seat Control Module that plugs in under the seat. The Factory heating pads that go under the upholstery (not yet installed for ease of troubleshooting). Backlights on the switches behind the cover. (Switches are back-ordered) The wiring is already there, per many other threads on this subject. There are also fuses in the under-glove-box fuse box.

There are two loose plugs under the seat that both fit – A 4 pin and a 2 pin., but there are two heating pads, and only 3 slots in the HSM (Heated Seat Module as I’m calling it). HSM has a 4-pin slot key’d one way, a 4-pin slot keyed another way, and a 2-pin slot. The 2-pin slot will take either the loose 2-pin plug under the seat, or the 2-pin plug for the lower seat heater. One 4-pin slot plugs into the seat wiring only, the other 4-pin slot plugs into the upper heating element only.
This leads me to assume that the 2-pin plug loose under the seat goes to nothing, (but I have not checked the wiring diagrams yet).

When I remove the button cover, I see the green backlight, but no orange temp-setting lights indicating anything happening, nor do I feel the heating elemets warming up.

I have NOT yet done Voltage checks on anything, nor have I looked at wiring diagrams. Haven’t really looked much into it because it’s been well below freezing, and my car is parked out front with almost a foot of snow on the ground… (I kneeled in the snow long enough to try the buttons with everything plugged in today, and no dice.)

I’ve seen that there may be software for the CEM, I’ve also seen that there is not software. No software is listed on Volvo’s Parts list, nor in the SS archive list of software.

If anyone with factory heated seats is willing to help me troubleshoot with voltage readings, etc, that’d be much appreceiated.