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Thread: Heated seats sometimes work e34

  1. #1
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    Heated seats sometimes work e34

    My heated seats in the 1990 535i used to work great on both settings, HI setting would about burn your arse! Then the car sat for about a year.

    Now they work, kinda, sometimes. I haven't felt it get as hot as it used to ever and most of the time it doesn't seem to work at all on either setting.
    sometimes if I flip it back n fourth it seems to get warm. I was thinking a relay or driver control module of some sort.

    What should I look at first? Any common issues with these?

    I have not checked passenger seat.

    The switch light does light up when going to hi or low heat and illuminates otherwise.

    I honestly havnt looked into it at all yet but just getting ideas.
    Last edited by darknezz7; 10-13-2018 at 04:38 AM.
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  2. #2
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    Cleaned the switch already? Spilt coffee/soft drink? It is easy to dis-assemble. 1990 built year is probably the older switch version without the electronics underneath, so just low, off, high.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
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    Seat heaters, like seat occupancy sensors, are rather fragile and failure prone anyway. A grid of heating wires that you sit on and flex every day is bound to give trouble. That said, shogun's right about the switch being a likely culprit. I've seen many switches become faulty after having a soda spilled on them. Rather than disassemble them, I take them out and swish them around in hot soapy water, then used compressed air to dry them. Electrical contact cleaner or even WD 40 works too.

    http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf (pages 148-149)

    There is a relay...two of them in fact. Strangely, the driver's seat heater relay gives power to the passenger seat heater relay, but the passenger seat heater relay gets its ground only when the seat belt is buckled!

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  4. #4
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    Ah, the two people I expected to comment on this subject and I most value their opinions.

    I feel like its the switch too as it seems to works if I mess with it.

    Thanks for the ETK link!

    I also know how finicky heated seats can be, but I've found some cars have specific failure points, *cough mostly fords cough* over others. So just checking.

    Thanks! I'l report back If I find anything

    Hery where are the relays and thats and interesting setup... So if anything is wrong with the drivers seat circuit the passengers will not work, or if your seat belt switch did not work.
    Slowly climbing the ladder. But never reach the top.
    Click Car 4 Build!
    '86 325es-Turbo m30!
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    '94 530i
    -6 Spd swp
    '89 Cherokee 4x4-4.7L stroker
    '97 Eclipse Spyder-4g64/63 stroker Turbo.
    '89 535is-RIP 2020, engine now in e30!
    '84 318is-RIP 2016.

    '89 535iA-Parted 2012
    94' 530iA-RIP 2004, engine in new 530i
    '78 530ia-first car RIP 2005

  5. #5
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    In many cases it is the switch. Nice method cleaning the switches without disassembling them, Chris.

    Also check the connections under the seat, on these old cars the plastic plugs/connectors are very brittle and fall apart easily. I have replaced most of the plugs.
    The seat heating mat of my driver seat had a broken wire and did not work anymore, in this summer I replaced it with a new carbon fiber pad, "performance" still to be tested this winter when it get's cold.
    Shogun tricks and tips for the E32 series are HERE!

  6. #6
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    Link to replacement heating element? Just in case.

    I'll probably clean the switch and put some die grease in the connections this wkend see if that helps.

    Are the relays under the back seat?
    Slowly climbing the ladder. But never reach the top.
    Click Car 4 Build!
    '86 325es-Turbo m30!
    '94 325iA-Clean DD
    '94 530i
    -6 Spd swp
    '89 Cherokee 4x4-4.7L stroker
    '97 Eclipse Spyder-4g64/63 stroker Turbo.
    '89 535is-RIP 2020, engine now in e30!
    '84 318is-RIP 2016.

    '89 535iA-Parted 2012
    94' 530iA-RIP 2004, engine in new 530i
    '78 530ia-first car RIP 2005

  7. #7
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    I used this DIY from the German 7-forum http://www.7-forum.com/forum/showthr...ghlight=carbon
    For removing the leather you can use this one http://bmwe32.masscom.net/sean750/Se...atSwapping.htm
    On my E32 I so far only replaced the seat bottom, not the back, that is still working.
    I am still using the original switch, cut off the wire from the original mat with a pigtail and soldered the wires from the new carbon mat onto these wires. These carbon heater mats are universal, the good thing is you can cut them to size.
    The old mat I left inside the seat, biggest problem is that the fine fabrics holding the old mat will crumble away, so you have to be inventive. The new carbon mat is on the cushion, then comes the old (not active mat) and then the leather.
    Something like this mat, I even got it cheaper, check ebay https://www.amazon.com/Carbon-Fiber-.../dp/B00FQTXJEE
    This DIY from an E39 will also help https://www.bimmerforums.com/forum/s...all-(complete)

    There are plenty of relays and modules under the rear seat driver side, see the above ETM page 0670.0-02 and 03, the following pages show you all relays. Under rear seat pass side are 2 fusible links, see my website for the details. One goes to the engine bay for powering the e-box, the other ones powers the box under the driver side rear seat.
    Some pics how it looks on E32, almost same on E34 http://bmwe32.masscom.net/johan/elec.../rearseat.html
    Last edited by shogun; 10-22-2018 at 09:52 PM.
    Shogun tricks and tips for the E32 series are HERE!

  8. #8
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    Cushion and back rest? If only one inop then I'd suspect the heating element.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  9. #9
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    Relay loaction, see page 7000.0-04 of ETM
    K65 driver seat heater relay - below driver's seat
    K66 passenger seat heater relay - below passenger seat
    Shogun tricks and tips for the E32 series are HERE!

  10. #10
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    Do you know where I can get bulbs for seat switches are they works with 12 V ? Thanks !

  11. #11
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    you mean the switches for seated heat?
    for lumbar support, sport seat switches, all older style seat heating switches, electric rear sunshade switch, memory switch you need T1 bulbs
    for sunroof switch, window switches rear. light switch, fog light switch: T1 1/4
    in case you have the newer seat heating switches, window switch block in front, they already have LED

    T1 1/4 bulbs should have 14V and 80mA
    for the T1 use 40mA, or for some switches 60mA is also ok.

    your 1990/02 bult date car has most probably the older seat heater switches.
    seat heater switch - old version
    Disassemble
    The small T1 bulbs are to be used. Important this time: Use those with 80mA! In the switch is a 50 Ohm resistor, which dims the bulb. With the above power you will get a good brightness. The full power is available at the bulb as soon as the button is pressed. Thereby the selected level shines brighter!
    Please do the disassembling only on a table and ideally on a plate with a high edge. Small balls and springs fall out of the switch en masse.

    all bulbs you can buy clear, if you need on some switches the "reddish" BMW color, use bulb color paint, the bulb shops have that. Google for online shops in your country for Miniature Light Bulbs

    as you are also registered on the German forum and you can see the pics there, here pics for disassembling of the old version seat heat switches, post # 11 https://www.7-forum.com/forum/showth...light=schalter
    Last edited by shogun; 11-17-2020 at 06:27 AM.
    Shogun tricks and tips for the E32 series are HERE!

  12. #12
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    Interesting, the switch on my passenger side heated seat (1990 735iL) was working when I first got the car, but the seat didn't heat up. Trying it again in the following weeks after purchase, the switch doesn't light up at all. I'm going to try cleaning it, and turning on WITH the seatbelt buckled. Hopefully the seatbelt not being buckled is the issue.

  13. #13
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    Yes I mean switches for heated front seats.

  14. #14
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    Quote Originally Posted by rbelton View Post
    Interesting, the switch on my passenger side heated seat (1990 735iL) was working when I first got the car, but the seat didn't heat up. Trying it again in the following weeks after purchase, the switch doesn't light up at all. I'm going to try cleaning it, and turning on WITH the seatbelt buckled. Hopefully the seatbelt not being buckled is the issue.
    Well I'll be. The passenger side heated seat works perfectly once the seatbelt is buckled in. That's all it was, in my case.

  15. #15
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    That is written in the owners manual: seat heating system will only operate when the engine is on, and in addition for the front passenger and rear seats only when occupants are wearing the seat belt. In view of the high power consumption do not operate the seat heating for longer than necessary.
    1988 owners manual, print no. 01 41 9 781 901 8/88

    Especially the older seat heating system uses a lot of power, the newer seat heating system on E32 with the seat heating switches with attached circuit board control are different.
    Shogun tricks and tips for the E32 series are HERE!

  16. #16
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    Quote Originally Posted by shogun View Post
    That is written in the owners manual: seat heating system will only operate when the engine is on, and in addition for the front passenger and rear seats only when occupants are wearing the seat belt. In view of the high power consumption do not operate the seat heating for longer than necessary.
    1988 owners manual, print no. 01 41 9 781 901 8/88

    Especially the older seat heating system uses a lot of power, the newer seat heating system on E32 with the seat heating switches with attached circuit board control are different.
    What year was the change over to the "new" switches/system?

  17. #17
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    you can check that on realoem very easy, Seat heating switch 61311374221 to 90/1990, 61311390888 from Sep '90
    search for pics, difference is easy to see
    Shogun tricks and tips for the E32 series are HERE!

  18. #18
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    Do you know how many volt get memory seat switch is very small bulbs inside the one is also red in it. I did install T1-1/4 size looks like not working ?

  19. #19
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    seat heating switch bulbs get 12V, better to use bulbs which can get 14V, they live longer.

    Memory switch is described here in post # 12, you are a member there and can see the pictures https://www.7-forum.com/forum/showth...light=schalter
    Memory-Schalter
    Hier braucht man Spezial-Werkzeug.
    Als Birne verwenden wir wieder die kleine T1. Ich empfehle euch hier, die mit 40mA zu nehmen. Es ist zwar nur eine Birne im Schalter und der Schalter ist sehr groß, aber: Die zu beleuchtenden Felder sind sehr klein (es leuchten nur die Ziffern 1-2-3, der Memory-Schriftzug wird nicht beleuchtet) und es ist wenig Platz im Schalter, was Probleme mit dem Wärmeabtrag einer stärkeren Birne machen könnte.
    Zerlegen:
    Das ist noch relativ einfach! Erst klipst man den Schalter an den vier deutlich sichtbaren Nasen aus. Man bekommt dann erst mal die untere Platine heraus (siehe Bild 1)
    Die obere Platine ist mit Kunststoffnasen fest. Diese sind bei der Produktion auch erst nach Einlegen der Platine angebracht worden - es gibt keinen Weg daran vorbei, diese zu entfernen. Es geht recht einfach mit einem Spitzen Messer oder einer scharfen Zange (Bild 2, Nasen schon entfernt)
    Danach kann man die obere Platine herausnehmen (Bild 3). Wer möchte, kann die Tasten auch entfernen und den Schalter gründlich reinigen. Dazu einfach etwas fester von oben die Tasten drücken, die rutschen dann schon raus.
    Auf die Platine kann (von der Rückseite) recht einfach eine neue Birne gelötet werden.

    Zusammenbau
    Alle Tasten wieder einlegen und die obere Platine auch reinstecken. Diese wird nicht fest halten. Dennoch rate ich dazu, den Lichttest jetzt zu machen. Die Birne hat keine Führung o.Ä. auf der Platine. Es kann also passieren, dass die Ziffern ungleich ausgeleuchtet sind. Das kann man korrigieren, in dem man die Birne etwas weiter in die zu schwach ausgeleuchtete Ecke biegt.
    Sobald das dann passt, muss die obere Platine fixiert werden. Ich habe länger experimentiert. Sekundenkleber, Heißkleber - all das hält nicht so wirklich solide.
    Mittlerweile nehme ich dazu Flüssigkunstoff (gibt es von Bondic, Soliq, diversen Homeshopping-Kanälen. Obi - das sind alles die gleichen)
    Diesen trägt man auf und härtet ihn mit der UV-Lampe aus (Bild 4). Auf Bild 5 sieht man den harten Kunststoffrand.
    ---------------------
    Memory switch
    Here you need special tools.
    For the bulb we use again the small T1. I recommend you to take this one with 40mA. There is only one bulb in the switch and the switch is very big, but: The fields to be illuminated are very small (only the digits 1-2-3 light up, the memory lettering is not illuminated) and there is little space in the switch, which could cause problems with the heat dissipation of a stronger bulb.
    Disassemble:
    This is still relatively simple! First you clip the switch off at the four clearly visible noses. Then you get out the lower circuit board (see picture 1)
    The upper board is fixed with plastic lugs. During production, these were also only attached after the board was inserted - there is no way around removing them. It is quite easy to remove them with a sharp knife or pliers (picture 2, noses already removed)
    After that you can remove the upper board (picture 3). If you like, you can also remove the buttons and clean the switch thoroughly. Just press the buttons a little harder from above and they will slide out.
    You can easily solder a new bulb onto the board (from the backside).

    Assembly
    Put all keys back in place and insert the upper circuit board as well. This will not hold firmly. Nevertheless I advise to do the light test now. The bulb has no guide or similar on the board. So it can happen that the digits are illuminated unequally. This can be corrected by bending the bulb a little bit further into the corner that is too weakly illuminated.
    As soon as this fits, the upper board must be fixed. I have experimented for a longer time. Superglue, hot glue - all that does not really hold solidly.
    In the meantime I use liquid plastic (available from Bondic, Soliq, various home shopping channels. Obi - they are all the same)
    This is applied and cured with the UV lamp (picture 4). On picture 5 you can see the hard plastic edge.

    Translated with www.DeepL.com/Translator (free version)
    Last edited by shogun; 12-01-2020 at 10:50 PM.
    Shogun tricks and tips for the E32 series are HERE!

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