W212 heated seat won't stay switched on

[a8hex]

Has anyone else had a problem with their heated front seats. Occasionally you switch the drivers seat heater on and a couple of seconds later it switches itself back off. Usually stopping the car, turning the engine off and starting again cures the problem, but occasionally it doesn't. I started doing it late last winter then I forgot when the weather improved so SWMBO stopped mentioning it. It came back this morning so I promised to have a look to see if it was a known issue, I could spot anything searching the forums here.

[goldieandblackie]

A relay of some sort failing or a fuse on its way out.

[donkmeister]

Does the 212 lock out comfort features when the battery is in a low state? I have a 211 and usually the first sign of a battery showing its age is that it locks out heated seats for the first few minutes following a cold start on a cold day.
But... You get a message and it just won't turn them on at all.

[DKL]

Battery maintenance, convenience functions are not available --- then convenience functions are now available.

This is what pops up on the screen on a 211. Leisure battery tends to be the culprit unless you have been doing short journeys.
But it does tell you and the seats (and other things) don't work at all so I'm inclined to say not that.

Seats will have a thermostat and a timer so maybe one of those?
STAR might have the answer if you hook it up and ask.

[a8hex]

goldieandblackie said:

A relay of some sort failing or a fuse on its way out.

A relay could be it, I hadn't thought of one of those. I'll check whether they run through a relay, I suspect they do. The fault seems to have become permanent now, sometimes after you switch it one it turns itself back off within a second or so, which is what it's done in the past, yesterday and today it would turn back off after about 10s.
The passenger seat one works fine and there are no other indications of issues with the battery.

I had a longer online search and found quite a few comments about the heated seats failing on early W212s and them needing new heater pads installing. The parts aren't too bad but I'm not sure how much I fancy taking the seat to bits. Hopefully MB will agree that it's covered my the warrantee. It's due for a service at the end of the month.

[a8hex]

a8hex said:

goldieandblackie said:

A relay of some sort failing or a fuse on its way out.

A relay could be it, I hadn't thought of one of those. I'll check whether they run through a relay, I suspect they do. The fault seems to have become permanent now, sometimes after you switch it one it turns itself back off within a second or so, which is what it's done in the past, yesterday and today it would turn back off after about 10s.
The passenger seat one works fine and there are no other indications of issues with the battery.

OK, I now know it can't be the fuse as both front seats are on the same fuse (12 IIRC) and the passenger seat works fine. Today it stayed on for a couple of minutes before switching itself off, first time. After that it just switched off immediately. Only a short drive, parked up for about 15 mins then drove back, tried again and it stayed on for a minute and half. I wonder whether it's failing as it starts to get warm.
Anyway I need to find a list of relays and their locations, I thought they'd be listed with the fuses but no.

[Jaysully10]

Hi did you manage to find a solution to this problem?

I’m having the same issue and could really use some direction.

Thanks