Heated seat not working

[DR-Z]

This afternoon I was playing with the driver's seat, just lifting the front up a little for comfort. Loosened the front and rear nuts/bolts and added some spacers. Then took the car for a spin and noticed the heated seat doesn't work. But it's OK on the passenger side. As far as I know there's just a single fuse for the two seats, and that's fine. Any ideas?

I too the seat out again and checked the wires underneath. Mine are manual seats, so just a few wires. Can't see anything loose.

 

[cj10jeeper]

Assuming you've not disconnected the loom to seat connector while working on the seat then, disconnect the feed to the seat and test 2 things with a meter:

Firstly check for currect supply to the seat when 'on' is selected. No current and you have the problem somewhere between switch and end of loom

Second test for continuity in the heater element. No circuit means one of the pads is bust and needs replacing.

If you 've not simply knocked to loom connector apart, then my guess is the latter given the passenger seat works

 

[DR-Z]

Makes sense. Not sure which is the heater supply cabling - I assume there will also be wiring to the seatbelt pretensioner (is there any danger of it going off if I disconnect it?) and the seat belt sensor.

It just seems a coincident that it should fail now, just after I've been 'playing' with the seat. If it is a seat pad, is this something that can be repleced? Or would it mean taking the leather off the seat?

 

[bcworkz]

Do the LEDs illuminate? If not, there could be a problem with the temp sensor circuit. Otherwise, as CJ explains. It would seem unlikely to me that both heat elements would have a fault at the same time, and they are connected in parallel, so you should have noticed one working and not the other. Replacement means removing the leather cover.

Pretensioner wiring has yellow connectors.

Another possibility if the LEDs are on is the supply voltage is low, causing the system to refuse to operate.

 

[DR-Z]

LEDs come on for maybe 5 seconds then go off.

 

[ranski]

LEDs come on for maybe 5 seconds then go off.

I had this recently when I fitted my new seats - the drivers side had the same problem by which the led heater light only stayed on for a brief time

If I can remember rightly I disconnected the battery (out of paranoia) and just reseated the connector under the seat - reconnected the battery and it worked

 

[DR-Z]

Thanks for the tip-will try disconnecting the battery tomorrow. Fingers crossed it works!

 

[DR-Z]

Just disconnected the battery, left it 10 seconds then connected again. Seats still not working, so more investigation needed. Bugger!

 

[cj10jeeper]

Bcw - you're right they are in parallels and 2 pads on the Zed. I've been working on my Jag and its one pad for base and back.

Unlikely to be both pads at once.




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[Stuart Truman]

Anyone know if there is a fault detection in the circuitry so it switches off in the event of a short etc. I know a short should blow a fuse, but just musing on it :?

 

[DR-Z]

Have had the seat out again this morning. Thorough check of wiring and connectors - no obvious breaks or shorts. ALso had the switch console out, just in case there was a short from when I fitted the Gaptech, although that was a while ago. Again, nothing obvious.

Still doesn't work. Would like to check out the seat itself for continuity, as cj10jeeper suggests, but not entirely sure which wires to check. Could really do with a wiring diagram. Theres a connector with a brown and green wire coming from either side, then another one next to it, also with brown and green but also a grey wire. What I don't want to do is trigger any other faults that I can't then clear, like the seat sensor. Or to set off the seatbelt pretensioner. Obviously I have to work live.

I don't have a code reader, but would this type of fault show up in a code?

 

[cj10jeeper]

Undo the seat. Disconnect the battery. Disconnect the loom. Remove the seat. Break down the compound plug and trace the 2 sers of seat pad wires. Check for circuit. Rebuild plug. Reconnect loom and then battery, refit seat.
Do not connect battery or turn on ignition while loom disconnected.

 

[DR-Z]

Did all of this. Seat circuit continuity is there, so probab;y not the heater pads. Inside the switch box there appears to be a small cicuit board. Maybe this has failed. Will see if this is a replaceable item.

And today is such a lovely day for a drive, but with last night's harsh frost I really need my seat heating!

 

[cj10jeeper]

I'd be looking at that switch next. Find a like for like replacement on EBay. Expensive at dealers.

 

[bcworkz]

Faults are stored in the switch centre. Even if a generic code reader found the module, it wouldn't be able to make sense of it. You need BMW diagnostic software for these sorts of errors. Take a look at the following link, there's info here and there that may be useful. Keep in mind the colour code abbreviations are in German, but many translate to English OK.

http://wds.spaghetticoder.org/en/e8385/Complete_vehicle/body/Seat_and_mirror_functions/Seat_heating,_driver%27s_side/

I'll take a shot in the dark and say it's an issue with the thermostat in the seat. Just because I've had more trouble with thermostat like devices in the past than any other single "technology". No idea really though. The fact the LEDs stay on for a bit tells me it's not a "hard" break or fault, that it takes a while for it to decide something's wrong and shuts down.

 

[DR-Z]

Thanks BCW. Finally managed to view these wiring diagrams, had to download IE9 first. Really useful link.

Your thermostat idea sounds logical, although not sure where this is (i.e.in the seat,or in the console?) and not sure how to check this out. Maybe a trip to the stealers needed.

 

[bcworkz]

There's one in both! You can locate the wire for the seat 'stat, see what the resistance is, and if it is the same as the other side. Not sure what else you could do related without tearing things apart. Nor how to identify the switch centre 'stat. Stealer may be an acceptable alternative, whatever codes have been stored would be useful info.

IE9? Bleh, sorry about that. For the SVG content?

 

[ranski]

If your looking to test another heater switch I can lend you a spare to test

It came with some seats that I bought, more so from a coupe so won't have the roof button - but should serve its purpose so you can test the seat heaters, so eliminating this from your fault fixing

 

[DR-Z]

Great offer - pm sent.

BTW, the wiring diagrams don't show any thermostats if I'm reading them correctly - unless it's the variable resistor.

 

[bcworkz]

Yeah, that's the bugger. Varies resistance by temperature. The one on the switch centre doesn't show because there are no external connections to it, but it does have one.