release the buttons on the dash. This is telling you that there is a connection issue of some sort. Luckily
the heated seat wiring isn't that complicated so it's fairly easy to determine what is causing the fault.
The fault is usually 1 of the following.
1 - Heated seat relay (microprocessor) failed.
2 - Poor connection between the heated seat relay and the relay holder.
3 - Poor connection to the heated seat.
4 - Poor earth to the heated seat wiring.
5 - Poor interconnection between seat base and seat back heater elements.
Swap the relays over. Normally the fault is only present on 1 side so swapping the relays (450 and Roadster) will either swap the side with the problem which would indicate a faulty relay or both sides start to function which indicates a poor connection to the relays. A spray of switch cleaner spray into the socket and the reinserion of the relays should easily be enough to clean any corrosion off the connections.
Check all of the fuses. The heated seat fuses are in the auxiliary positions on the side of the SAM unit however, check all of the fuses as a precaution.
Take your multimeter (well go and buy one then), set it on volts. Disconnect the black heated seat connections under the seat (this is NOT the red, yellow, orange or pink connections. If it's a danger colour, leave it plugged in). Push 1 multimeter probe into each of the 2 pins and hold them there. With the car ignition to position 1 press and hold the heated seat button on the side you are testing.
You are looking for a reading on the multimeter to show about 12 volts. If you do then that's good. If you don't then you don't have power getting to the seats and your life just got complicated (in other words, give up as there is a faulty wire somewhere).
Take the multimeter and put it into continuity checking mode. There is usually a beeper with this mode. This mode tests whether a wire is conducting a voltage or if it has a break in it. Take the heated seat cable that comes from the seat and place 1 probe on each of the connections. If the seat heating element is ok you should get a beep from the multimeter or a reading on the screen.
Ian2726's multimeter said that he had a break in the element so he looked into it a bit further. On removing the seat he noticed that there was a connection between the seat base and the back. This connection had pulled apart which had broken the circuit. Push the connection back together and retest the seat heater.
Clean the connections for the heated seat relays and the connections to the heated seats.
Both of these are prone to corrosion which will increase the resistance of the connection.
Due to the microprocessor control of the heated seats, they are more sensitive to poor connections.
Cleaning of the connections is best done using a switch cleaner spray. Spray it on both connectors
and then insert and disconnect the connection a few times to allow the friction to clean the contacts.
Allow the switch cleaner to evaporate before reattaching the connection or refitting the relay.
Check the continuity and the tightness of the earth points to the car. Look for obvious wire damage.
Disconnect the heated seat connector, put your multimeter on continuity testing (Ohm symbol).
Put 1 probe on the earth wire (brown) going to the car and the other probe on the battery negative terminal.
You should get a very low resistance reading and/or a beeping noise depending on your multimeter.
This denotes that the connection is OK. A high number will mean the connection is poor.