I have a 850 aswell and my seat heaters did not work either. I checked around and found out that there was a recall for the seat heats and something to do with the gas tank. Call your local Volvo dealer and see if all of the rcalls are up to date. Hope this helps. Oh yeah, aftet I sent my Volvo in the seat heater work now my butt can be warm.

This is my boiler plate test for seat heaters. I will try to add pictures but I don’t know if they work here or not (EDIT - They don't so ignore references to pictures). In your case I would add the step to check the Yellow/Red wire on the gray connector for voltage. If it reads battery voltage, as has been suggested, the ground is bad. If you actually suspect that use a ground other than the plug to make the measurements described.

Look under the seat, on the right hand side as you look at it from the footwell, and locate the power connector for the seat.
It is the large white connector with the Yellow/Red wire and the Black wires.

Use a Voltmeter and, with the seat heater switch on and the key on, check for battery voltage between the Yellow/Red wires and the Black wires. If it measures good there it means that the switch is good and the wiring to the seat is good.

You next need to locate the heater pad plugs, they are just below the front edge of the seat, they are both 2 conductor connectors. One connector is gray and the other is black.

Backprobe the red wire on the black connector and check it for battery voltage as well, the black wires on the power connector are a good ground point for the meter.

If you have good voltage there it means that the thermostat and its circuit are good. If you don't have voltage there it means that the thermostat is bad (not likely) or the wiring to the thermostat has come unplugged (more likely). The thermostat is located near the rear of the bottom seat cushion and it has a Red wire and a Red/White wire going to it. Plugging it back in is tricky and is best accomplished from the back seat and having someone sitting in the seat - that someone will get goosed a bit.

Assuming that the voltage is good on the red wire next move to the yellow wire. On a normally working system you should read voltage there but it will be less than full battery voltage.

If you read full battery voltage on the Yellow wire then the seatback heater element has burned out.

If you read no voltage there then the seat bottom heater element has burned out.

...Lee

Could easily be a bad ground: If you have 12v on both sides of the element, then
the ground-side connection is probably broken. You should be able to find 0 ohms
from one side of the element to the frame of the car.

and there are no broken elements...


How do you know this ? ? ?


If you are getting power to the element, but no heat from the elements, doesn't it stand to reason that the elements are bad?