S204 Heated seat replacements

[martini]

My Passenger seat heater has stopped working. The backrest still works. Anyone know how to test /repair.
Car is 2012 C350 cdi leather and memory pack.

 

[DSM10000]

if you can get ot the connector for the seat pad you could check for continuity and if it fails then you will need to remove and replace the heater pad. They fail eventually, especially if someone kneels on them.

 

[martini]

Thanks for that. I did have a look to identify the connections, however the wiring under the seat is a maze.
Has anyone had a dealer do a replacement. Is it just a question of getting a trimmer to remove and replace the pad?

 

[MrGreedy]

I'd go for a trimmer myself unless you like a challenge and need to save the cash/it won't happen if you have to pay for it. I did both front seats in my Insignia over Christmas.

I ended up taking them both out of the car so I could test continuity across everything. You should be able to touch one pin with the red tester lead, and every other remaining pin (if you don't know what the corresponding pin is), and one of them should give continuity. If it doesn't, there is a break somewhere.

Usually there are 3 connector pairs (male and female) with just 2 pins, and these correspond to seat back, seat pad, and temperature probe. Two should look the same (the seat heating elements) and the third will be for the probe, and you would need to measure the resistance.

Assuming it is the heating mat (most likely), this is your list of challenges:
- take the seat out of the car (de-activate airbags using decent code tool, remove plastic trim on base, seat belt, airbag connector and any wiring connectors, then unbolt and lift out without scratching something - top tip, drape several thick towels over all of your interior surfaces to offer a chance of protection!! but still be very very careful, ideally two-person lift and don't kneel on the other seat)
- check that there is NOT continuity across the heated seat mat
- buy the correct mat (I'd just get a quote from MB Grangemouth for best price, and there won't be any aftermarket supply of suitable mats)
- de-upholster the chair base (fiddly, especially for the novice)
- remove the old mat (glued on) and fit the new mat (usually a sticky back)
- re-upholster the chair (fiddly, and very hard on the hands and grip, and you will need hog rings and hog ring pliers I would expect to do the job properly)
- re-fit the seat into the car

The tricky bit will be identifying exactly what's not working (I still would first guess the heating mat), so that the trimmer can just crack on. I'm guessing a trimmer will not want to do electrical fault finding, but maybe I'll be proved wrong.

Took me 4x6 hour days to do both as it was my first attempt and testing and working out what to do. I could probably do one in 4 hours now. I scuffed my steering wheel whilst removing the seat, thankfully on the underside and minor, but I was trying to be careful and didn't think about the thick towel trick!
I also took the opportunity to cut out some seat foam that was crumbling and shot, and refitted a new piece cut to shape, stuck together using a triple application of contact adhesive on both pieces before sticking. It seemed to be incredibly well stuck, so I was satisfied with the repair.
I had a seat back in one chair, and the seat base in the other. Testing obviously required to eliminate, and watched many YouTube vids to work out what I needed to test.
The temperature probe is usually stuck together in the heating element mat, so that will simply be changed as a matter of course at the same time.

 

[MrGreedy]

Thanks for that. I did have a look to identify the connections, however the wiring under the seat is a maze.
Has anyone had a dealer do a replacement. Is it just a question of getting a trimmer to remove and replace the pad?

A dealer would just sub-con this out I suspect.