Avensis T25 passenger seat heating problem

[morpheusro]

Hi Guys,

This evening I noticed that the passenger seat heating is not working anymore. Since I am a newbie, but I want to try to fix the problem myself, I would like to ask advice on how to diagnose the problem?

I have checked the fuses, but they seem OK, however, is dark now, so I will re-check them again tomorrow to be sure. The car is LHD if that's important...

Thank you!

[Gerg]

I have completely removed the seat heater element on a 2015 Auris.  Anything I have seen may be relevant to an Avensis, but maybe it won't....

On the Auris there are two heat settings.  This is acheived by having two seperate thermostats, and two power feeds - one to each thermostat.  If one of the thermostats had failed, then the seat should still work on the other setting, they share the same heating elements. So this is easy to diagnose.

There are 3 connecting wires for the complete seat heater on the Auris:  Ground (black),  12v (low-heat, I think) grey,  12v (high-heat, I think) red.

Measuring across the seat heating element at the power connector will give a reading of around 4 Ohms from either of the power feeds to the ground wire.

The two heating pads (seat-base, seat-back) are wired in series - if one fails they both stop working.

From a Toyota dealer repair point of view, I am fairly certain that the seat heating element is replaced with the foam pad it is attached to - they are not seperated out.  I doubt the heating element is available, new or used, on its own. 

I have taken the seat heating pads out of a seat - it is loosely attached under the seat fabric cover with small plastic tags (like are often used on shop price tags for clothes), but the seat cover itself, is attached to a metal frame that is embedded in the seat foam, by metal rings.  I really doubt that these rings are meant to be taken off, but they can be with some effort, there are plenty of them.

The best access to all the seat electricals is at the seat bottom/back (after unzipping the the rear seat panel/cover), and underneath the seat.  Any wiring under or inside the seat that is yellow is best left alone - it will be for the airbag and SRS seat belt tensioner arrangement (if fitted)!  If there is any suggestion that your car has airbags in the seat, then extra caution is required - disconnecting the 12v Battery, and waiting 15 minutes is best practice if you are working anywhere in the area of an airbag.

In this picture of the Auris heater, the seat base-heater is on the right, the back-heater is on the left.  The gaps in the cloth are to accomodate the attachment points for the seat fabric.  The thermostats are small circular items, located very close to where the cabling joins the cloth on the seat base-heater, under an extra layer of white cloth.  They are completely sealed, and soldered into the circuit, one is yellow, one is orange.

 

If you decide that it is the element has failed (the most likely situation, I think) then you have to work out how to repair it, which could be challenging!

Best of luck.

[morpheusro]

Thanks for the answer, very thorough! I will save it for future reference.

It seems I missed the fact that the seat has some sort of weight sensor, as it does not heat when nobody is sitting on it, but once you sit it starts heating up, and now it works.

Only the light for the heat level is not working. I believe there must be some light bulb that I can replace?