Seat Heater Too Hot

Instead of having high and low settings, the Gen 3 Prius seat heaters cycle. They do get hot but then cool down some and then get hot again. Is it possible that your drivers seat is not cycling properly? My wife, who is sensitive to such things, commented on how hot her seat got but then decided that she likes the cycling. Our other vehicle has high and low settings with the high setting too high for ongoing use.

 

We had the same problem with our 2012. I took it back to the dealer where we purchased and they ran the "temperature tests" only to tell me they couldn't find anything wrong. I then took it to the local dealer (where we purchased our 2008) and they did the "butt test" - the service guy actually sat in the seat - no fancy instruments needed. He removed the seat cover and found that the seat heater had bunched up in one location - likely when the cover was put on the seat. They replaced the heater element (believe it was the seat bottom, but reused the "pleather" cover). No problems for 4 years now!

 

And, if worse comes to worse, it may be possible to do a in-line "resistor" to clamp down on the voltage going to the heating element, making it get "less hot" when running.

 

I'm pretty sure the cycling limit-switch is built in for safety requirements. The Plug-in Prius does offer high and low settings, and the wiring diagram shows limit switches for both settings....

If you know anybody with a thermal imager (things like the FLIR ONE are crazy cheap now, at least compared to anything from a few years ago), it would be really easy to see whether the heat traces are bunched up in some way ... just turn on the heat and point the imager at the seat. You see the heat trace pattern very clearly. The normal pattern is a little denser in the areas where you'd expect.

I respect the trade-off the engineers had to make on the heat power. In a good Indiana cold snap, the power is barely enough to notice, I can get all the way home without the seat feeling warm ... and then in merely chilly weather, it's overpowered and it does cycle too-hot...off...too-hot...off, which to me is annoying, I'd rather be able to turn it down to a lower output where it would never hit the limit temperature, and just stay steadily on.

Probably the nicest solution would be to wire in adjustable heated-clothing temperature controllers (after measuring the power draw of the Prius heat pads and confirming the controllers can handle it). The controllers use rapid pulsing to vary the output, rapid enough that it doesn't feel like cycling on and off, and they do it without getting hot themselves (no current flow during the off pulses, no resistance to speak of during the on pulses).

I wouldn't recommend just trying to put a resistor in series, because that will get significantly hot, calling for some careful thinking on the resistor size, ventilation, and mounting to protect materials nearby.

-Chap

 

Our 2010 has 2 settings: off and too hot.

Our '06 Sienna has a thumbwheel with about 6 clicks to adjust the heat. A much better arrangement.

 

Sooner or later, somebody's gonna try those heat controllers....

-Chap

 

You would think that your dealer could at least pull your cover to take a look.

Here is an option that you can install yourself. It has 5 heater settings and costs $90.

2 seats heated seat,seat heater fit Toyota Prius Corolla Camry,Yaris,landcuriser | eBay

 

I'd almost hope at the dealer someone would have a thermal imager these days, to be able to take a look in seconds without pulling the cover.

As someone who has dealt with the hog rings on car seat upholstery before (and I was not being paid dealer tech wages to do it!) ... the labor saved cussing at just one or two seats worth of hog rings ought to pay for one of the newer cheap imagers.

-Chap

 

YES!! Mine is painfully hot, both driver and passenger side. I don't know if it cycles because I can't tolerate the heat for more than 2 or 3 minutes. I'm bringing mine in for service soon and will ask if it can be adjusted.

 

mine has hi and low. they're both too hot. i just toggle it on/off as needed.

 

That's what I do. I press the start button. Turn on the driver's heated seat. Then start my commute. After about two or three minutes, at a traffic light, turn off the seat. It's plenty toasty, by then, the car's heater starts to kick in. May not be ideal, but the heated seat is still appreciated.

 

I do the same. My wife however likes it on continuously, and I'm convinced will eventually spontaneously combust.

 

My seat heater also had only on and off. After a few minutes it gets uncomfortable so I switch it off (the car heats up anyway) so I never tried if it would cycle at a certain temperature.
It is not a luxury heater with different heat settings. It is on and off, so on must generate enough heat even when it is -20.