Heated seat not working

[Jay 535i]

Driver's side is fine, but no action at all on the passenger's side. Pressing the rocker switch in either direction causes the light to go out rather than become brighter. Any tips? My wife's bum is cold.

[Scott H]

1) Fuse under rear seat (unlikely since the seat works and the switch is lit)
2) Switch has gone bad (~$30 from BMA)
3) Heating elements are shorting out. This can happen from moisture corroding the element coils.

As usual, start from cheapest.

Also know that the switch is different on later cars.....make sure you get an early one.

Also check to make sure all of your wiring harnesses are securely plugged in under the seat.




Driver's side is fine, but no action at all on the passenger's side. Pressing the rocker switch in either direction causes the light to go out rather than become brighter. Any tips? My wife's bum is cold.

[rreimund]

good stuff.. I've got the exact same problem.. None of the heater settings work, but the switch lights up with the headlights, and when you turn the rocker switch "on" the illumination goes out when it should get brighter..

Looks like I'll be checking fuses (again), harnesses and getting a new switch..

[Jay 535i]

Thanks!

I take it a bad switch is a pretty common occurence, and the most likely culprit? I'll get one from BMA.

:)

[Alan_525i]

Also do note that her seatbelt must be buckled for them to work. Possible that the sensor in there isn't working. Kind of BMWs encouragement to be safe.

[Jay 535i]

Also do note that her seatbelt must be buckled for them to work. Possible that the sensor in there isn't working. Kind of BMWs encouragement to be safe.

Really!? That's very interesting. Any way to test that sensor?

Strange 'feature'...

[Scott H]

There are seat occupancy sensors in later cars which help with determining airbag deployment, etc.

There is a sensor in the seat belt clasp but it has never needed to be connected to have the seat heater work in my 1989 535 or my 1991 M5. I'm pretty sure Alan is mistaken at least when it comes to the E34


Really!? That's very interesting. Any way to test that sensor?

Strange 'feature'...

[Qube]

That's EXACTLY the problem I have too. I posted somewhere in another thread (not a fix).

[Jay 535i]

That's EXACTLY the problem I have too. I posted somewhere in another thread (not a fix).

Okay, there should be enough of us to figure this out... :)

I'll get a new switch and see what happens.

[Qube]

No kidding.

I'll check the wiring loom under the seat tomorrow when it's drier. In the mean time, I need to see why the driver side only goes on maximum heat setting.

[Bill R.]

look at the heater circuit here, the passenger needs the seat belt buckled to work...http://www.bimmer.info/%7Ebill/seat%20heater.jpg




There are seat occupancy sensors in later cars which help with determining airbag deployment, etc.

There is a sensor in the seat belt clasp but it has never needed to be connected to have the seat heater work in my 1989 535 or my 1991 M5. I'm pretty sure Alan is mistaken at least when it comes to the E34

[Qube]

Right, but that doesn't explain the light on/off behavior. Pushing either low/high shouldn't turn off the light but rather make it stronger... :| something is wrong.

[Jay 535i]

Right, but that doesn't explain the light on/off behavior. Pushing either low/high shouldn't turn off the light but rather make it stronger... :| something is wrong.

And, FWIW, my wife does use her seatbelt. :)

[Bill R.]

seatbelt switch is working since the seat heater relay won't send power to the seat heater without it., then once you know the switch is working you verify that your getting power from the relay to the seat heater switch itself.





And, FWIW, my wife does use her seatbelt. :)

[Kalevera]

Right, but that doesn't explain the light on/off behavior. Pushing either low/high shouldn't turn off the light but rather make it stronger... :| something is wrong.
I don't have a diagram of the switch (earlier or later) itself, but it's quite common for one of the LEDs to burn out, thereby having a partially lit switch (light pattern can be anything) without affecting the operation of the seat heater.

This is also applicable to the lumbar switch.

I've seen it happen both ways -- lights are fully operational on the switch, yet the action for the seat function is still bad; lights are sort of or not operational, yet the seat function is fine.

I've tried to R&R two of the early ones with no success. The later units seem more complicated. It's easier to buy a new replacement.

One easy thing to do when testing is to swap between the working and non working seat (in such cases), which is what I'd be doing if I were Jay. Swap the driver's (known working seat switch) onto the pass seat. Takes 5 seconds and a bit of luck with a trim puller to lift the switch (the metal tabs are inverted, so another instrument has to be worked in there to pop the switch out). The harness connectors can be brittle and bitchy, however.


best, whit

[Scott H]

wonder why seat heaters work on both of my cars regardless of someone being in the seat with a seat belt clicked in or not.

Also functions similarly on other E34s I know.

Looks like the driver's side doesn't operate the same way??



look at the heater circuit here, the passenger needs the seat belt buckled to work

[Qube]

One easy thing to do when testing is to swap between the working and non working seat (in such cases), which is what I'd be doing if I were Jay. Swap the driver's (known working seat switch) onto the pass seat. Takes 5 seconds and a bit of luck with a trim puller to lift the switch (the metal tabs are inverted, so another instrument has to be worked in there to pop the switch out). The harness connectors can be brittle and bitchy, however.
best, whit

That is an awesome suggestion. Didn't even think about that one! Just hope it doesn't crumble when I try and take out the driver side ;)

[Bill R.]

belt buckled to complete the circuit for the heater relay but then again where i'm at the seat heaters aren't usually a big issue..:)




wonder why seat heaters work on both of my cars regardless of someone being in the seat with a seat belt clicked in or not.

Also functions similarly on other E34s I know.

Looks like the driver's side doesn't operate the same way??

[Anthony (M5 in Calgary)]

[QUOTE=Bill R.]belt buckled to complete the circuit for the heater relay but then again where i'm at the seat heaters aren't usually a big issue..:)[/QUOTE

Early seat heater switches are on/off where later ones are momentary with timers that kick from high to low after a few minutes. The passenger seatbelt interlock keeps the seat heater from running without an occupant, saving heater's life expectancy. Obviously not an issue in the driver's seat as it is unlikely the car will be driven with this seat empty...

[rreimund]

interesting about the passenger seat being tied to the seat belt.. I'll have to test it with the seat belt fastened... maybe that's all I needed to do.. ( not likely)

[Jay 535i]

Thanks, Whit. I'll try that. Hope I don't break anything..

[rreimund]

Haha!!! Awesome.. my passenger seat DOES work.. just needed to have the seatbelt buckled... Thanks everyone!! Jaylebo - How'd yours do?

[Qube]

Unfortunately heated seats is a low low priority at the moment. Be a few days before I get it back.

[Jay 535i]

Haha!!! Awesome.. my passenger seat DOES work.. just needed to have the seatbelt buckled... Thanks everyone!! Jaylebo - How'd yours do?

Well, I know it's not that I've been forgetting to buckle the belt, because I do. It might be the switch. I'm gonna try swapping the left and right ones to see if that does it. I'm just not really sure how to get the switches out of their homes.

[Kalevera]

Pull the cover off of the side of the seat if only a Torx t15/t20 (forget what size it is) bit is available. Two screws on the side of the trim, and it's held in place by two or three plastic pins at the bottom -- don't worry about them, just undo the torx screws. That gives enough clearance to reach in and pop the switch out. The seat adjustment has to be played with to get a driver on those screws with the seat still in the car, though.

best, whit

[Jay 535i]

Pull the cover off of the side of the seat if only a Torx t15/t20 (forget what size it is) bit is available. Two screws on the side of the trim, and it's held in place by two or three plastic pins at the bottom -- don't worry about them, just undo the torx screws. That gives enough clearance to reach in and pop the switch out. The seat adjustment has to be played with to get a driver on those screws with the seat still in the car, though.

best, whit

Thanks!

[seks69]

I have just the opposite problem.
My passenger seat heater works until I plug the seatbelt in.

Any ideas?