I don't know exactly when it started since I haven't used the heated seats all Summer.
I wanted to use them recently and found both are not working.
The buttons on the climate control module work, they light up to indicate three levels of heat.
I have checked the resistance through the base and the back heating elements for both seats.
I have verified power and ground at both heated seat modules as well as checked both fuses.
I do not have power output from the modules to the heater elements.
I have confirmed continuity in the wires from the climate control module to the heater modules.

What I'm not sure about is the seat temperature sensors and how to check that they are reporting to the modules properly
or if the climate control module is actually telling the heated seat modules to turn on the elements.

Does anyone have any suggestions of where to go from here?

 

Update: Solved the problem, thought I would post the solution should anyone else ever experience this.

A few months ago I had a heater core leak and had taken out the entire center console as well as the climate control module in order to replace the o-rings.

Apparently, this caused the Climate Control Module to forget which trim level of XC70 it was installed in.
I used the generic scan tool at the shop I work and found a couple codes for "Wrong component installed" in the CCM.
I went into current data and found that data pids for
Drivers seat heater module - not expected
Drivers seat ventilation module - expected, not detected.
and the same data for the passenger seat.

However, my car doesn't have the ventilated seats.

I was able to use the scan tool to run the HVAC System Calibration and the heated seats immediately began working.
The only part of the entire climate control system that was not working was the heated seats, but apparently the CCM couldn't tell the heater modules to turn on the seats because it was trying to communicate with the wrong kind of module.