Troubleshooting a Heated Car Seatby Cassandra Cochrun
Problems with heated car seats almost always occur in the seat heater element, instead of in the seat heater switch. However, checking the seat heater element requires taking the car seat apart, so you should begin by checking for other problems, working your way to the seat heater element as a last resort.
When you begin the troubleshooting process, the first thing you should do is inspect the fuses. If a fuse is blown, replace it immediately. If that isn't the problem, check the electrical plug underneath the heated seat where the seat plugs into the main wiring harness. Be sure that all the plugs in the heated seats are free of corrosion or dirt that may inhibit them from working correctly. You can also check to be sure that there are 12 volts coming from both sides of the switch for the heated seats while the switch is on. If there aren't 12 volts, you know that the switch is bad, although this is rarely the case.
If the plugs on the seat are free of dirt and corrosion and the heated seat still isn't working correctly, you need to turn the car's ignition to the "on" position and check that there is power to the plug. If there is power to the plug, and there aren't any other problems, you know that the problem is in the seat itself. You can also check for continuity between the plugs. There should be three pins in the vehicle wiring harness under the seat. Use a continuity tester to determine whether there is continuity between the pins. If not, you have an electrical problem.
Once you know that the problem is in the seat, you may remove the seat cover to examine the heater. The thermister's job is to sense the temperature of the seat and adjust the heater accordingly. Be especially mindful of the thermister's location in the seat. If the thermister isn't precisely in the correct location, it won't sense the temperature correctly, and so the heated car seat may not work properly. You can check with your owner's manual to be sure the thermister was in the correct location to begin with. If the thermister wasn't in the correct location, it may have caused the heater wire to burn out.
A problem with the heater element itself is the most common cause of problems with heated car seats. This is because the heating wire that heats car seats is usually small and quite fragile, making it susceptible to breakage over time. If, when you remove the seat cover, you see burn spots in the fabric that covers the heater element wire, you know there's a break in the circuit. You can replace the heater element wire, or you can repair it by soldering the broken spot back together, then covering it with electrical tape and heat shrink wrap.