Seat Heater Diagnosis

[saved4it]

Anyone with some experience on the seat heaters give me some advice? I think I did a decent diagnosis, but before I order a replacement part, I thought I'd double check here.

Last night my wife and I were out and we both tried to use the seat heaters. The passenger side worked with the red light coming on. The driver's side clicked, and the red light lit briefly before going out. Every time I clicked it, it would do the same thing. Her's got warm. Mine didn't. Today I decided to figure it out rather than rely on the dealer.

Obviously the fuse isn't the issue since her's worked. I doubt the rocker switch is bad. Took the seats out and found the wiring that went to the relay for the seat heater on the driver's side. Disconnected the relay (pain in the butt!) and identified the leads that provided the voltage from the car's electrical system to the relay. It read 11.5V on my multimeter, so that seems like it's getting the appropriate amount of electrical potential. Next I found the wires for the seat heater elements on the butt and the back. Decided to test resistance on the heater elements. The butt seat read 1 ohm. The back read infinite resistance. Hmm...

I then figured out how to take out the back heater element (PN 996 521 531 01). Put it on the passenger side and tried the seat heater rocker switch. Aha! Now the passenger side blinked. I believe the only thing wrong is the driver's side back heater element.

If I buy that piece and reinstall, do you think I have it beat?

[1schoir]

Anyone with some experience on the seat heaters give me some advice? I think I did a decent diagnosis, but before I order a replacement part, I thought I'd double check here.

Last night my wife and I were out and we both tried to use the seat heaters. The passenger side worked with the red light coming on. The driver's side clicked, and the red light lit briefly before going out. Every time I clicked it, it would do the same thing. Her's got warm. Mine didn't. Today I decided to figure it out rather than rely on the dealer.

Obviously the fuse isn't the issue since her's worked. I doubt the rocker switch is bad. Took the seats out and found the wiring that went to the relay for the seat heater on the driver's side. Disconnected the relay (pain in the butt!) and identified the leads that provided the voltage from the car's electrical system to the relay. It read 11.5V on my multimeter, so that seems like it's getting the appropriate amount of electrical potential. Next I found the wires for the seat heater elements on the butt and the back. Decided to test resistance on the heater elements. The butt seat read 1 ohm. The back read infinite resistance. Hmm...

I then figured out how to take out the back heater element (PN 996 521 531 01). Put it on the passenger side and tried the seat heater rocker switch. Aha! Now the passenger side blinked. I believe the only thing wrong is the driver's side back heater element.

If I buy that piece and reinstall, do you think I have it beat?

Your steps sound pretty definitive in making the correct diagnosis.

If you want to make 100% sure, why not put the passenger side seat heater element into the driver's side seat and see if that works correctly?

Then if you want to save a little time on the labor, you can just install the new element that you buy into the passenger side seat.

Regards, Maurice.

[saved4it]

I was going to try exactly that -- to put the passenger side into the driver seat, but the wiring for the heater element was totally routed some bass-ackwards way through the lower part of the seat. I could not figure out how to take apart the seat bottom without destroying clips, so I opted not to do it.

Now to find a place to procure the part.

[jpflip]

Anyone with some experience on the seat heaters give me some advice? I think I did a decent diagnosis, but before I order a replacement part, I thought I'd double check here.

Last night my wife and I were out and we both tried to use the seat heaters. The passenger side worked with the red light coming on. The driver's side clicked, and the red light lit briefly before going out. Every time I clicked it, it would do the same thing. Her's got warm. Mine didn't. Today I decided to figure it out rather than rely on the dealer.

Obviously the fuse isn't the issue since her's worked. I doubt the rocker switch is bad. Took the seats out and found the wiring that went to the relay for the seat heater on the driver's side. Disconnected the relay (pain in the butt!) and identified the leads that provided the voltage from the car's electrical system to the relay. It read 11.5V on my multimeter, so that seems like it's getting the appropriate amount of electrical potential. Next I found the wires for the seat heater elements on the butt and the back. Decided to test resistance on the heater elements. The butt seat read 1 ohm. The back read infinite resistance. Hmm...

I then figured out how to take out the back heater element (PN 996 521 531 01). Put it on the passenger side and tried the seat heater rocker switch. Aha! Now the passenger side blinked. I believe the only thing wrong is the driver's side back heater element.

If I buy that piece and reinstall, do you think I have it beat?

You did a perfect troubleshooting. I just look at the wiring diagram, and the seat element is connected to a control unit with a thermostat in it. I hope you did a good check of the electrical wires for damage or chafing etc. because a Porsche TSB # 9757 mention the addition of a bracket to prevent the wire bundle from being damaged while operating the seat...

[jpflip]

I was going to try exactly that -- to put the passenger side into the driver seat, but the wiring for the heater element was totally routed some bass-ackwards way through the lower part of the seat. I could not figure out how to take apart the seat bottom without destroying clips, so I opted not to do it.

Now to find a place to procure the part.

With your part# I just look at Pelican and they got the part for $109.25

Edited January 11, 2010 by jpflip

[saved4it]

Yeah, going to call McKenna tomorrow to see if they have it in stock. Otherwise probably an order in to Pelican. I will have to take out the seats again anyway to reinsert the cables back into the retaining clips along the side of the seats (forgot, but no biggy since I am not driving anywhere). Yeah your wiring diagram confirms pins 5 and 9 to test for voltage and then 5 and 3 to test for resistance overall. Is that little bridge between the heating elements the thermostat? Is that what gives the resistance of 1 Ohm?

[jpflip]

Yeah, going to call McKenna tomorrow to see if they have it in stock. Otherwise probably an order in to Pelican. I will have to take out the seats again anyway to reinsert the cables back into the retaining clips along the side of the seats (forgot, but no biggy since I am not driving anywhere). Yeah your wiring diagram confirms pins 5 and 9 to test for voltage and then 5 and 3 to test for resistance overall. Is that little bridge between the heating elements the thermostat? Is that what gives the resistance of 1 Ohm?

You cannot get to the two back element wires (red and white pins 1 and 2) and see if it is open or closed???

Edited January 11, 2010 by jpflip

[saved4it]

Don't understand what you mean. I already tested wires 1&2 on the heater elements and the backrest one didn't give a reading, therefore it is bad.

[jpflip]

Sorry I didn't understand that part. Of course if you don't have continuity on the element itself you got your problem right there. Let us know how difficult it is to replace the element, Good luck.

[saved4it]

Sweet, Beverly Hills Porsche had the part and, because it was a special order that no-one ever picked up, they let me buy it for $95 (better than Pelican!). I will post some pictures later on how the upholstery comes off the old element and goes into the new one. It does not seem too hard, but there are little wire clasps that might need to be pried off with a pair of pliers. More later!

[saved4it]

So, here's an update. I managed to swap out the bad seat heater element (see picture with perfect resistance) and rebuild the seat-back upholstery. This took about 90 minutes with lots of care and testing. The seat heater element itself is sandwiched between the leather upholstery and a white plastic backing on which there are hooks to attach the leather upholstery. You have to undo the cloth from these hooks, then undo 9 metal clasps in the middle of the seat-back that also attach the upholstery to the white plastic. These metal clasps were a pain in the butt to remove (see picture). I wound up using a thin screwdriver to separate them and then pliers to wrench them off and squeeze the blue upholstery felt thingy (technical term) off the white plastic mold.

Once everything was apart, I noticed a burned section on the heater element (see picture). Bingo! The thing that surprised me with this is how close the heater element is to the upholstery and the driver's body. Wow! I can imagine sweat building up there, possibly contributing to a short. On the other hand, my wife loves how fast my seat warmers work. Trade offs!

Swapped in the new heater element (see picture), which tested some resistance. The trick was to get that upholstery back on, without undue wrenching to the heater element (didn't want to screw up the new one by bending wires). I decided to upgrade to the high-tech plastic zip-ties (see picture). Positive benefit: a 1 gram weight savings. I think I'll feel that!

Everything is back together and the seat-back still tests 1 ohm or so. Daylight gone, so sometime this week I'll take the seat out and install it. Wish me luck, although I feel I have this conquered.

[jpflip]

Good job! And thanks for the information and pictures...

[1schoir]

Thanks for taking the time to post the procedure and the photos. :beer:

I'm 100% certain that this will help future posters who run into this problem.

Regards, Maurice.

[saved4it]

Just a quick note to say that the seat heater is fixed. It sure is easier to take the seats out and dismantle stuff once you've done it a few times.

[kcsporsche]

Have the exact same problem. Drivers side blinks on then off. Passenger side works fine. I removed the passenger side seat heater and plugged it into the drivers side and still the switch will blink on then off. Any suggestions on what to check next? And yes, trying to route the passenger side harness out was a pain in the .

[1schoir]

Have the exact same problem. Drivers side blinks on then off. Passenger side works fine. I removed the passenger side seat heater and plugged it into the drivers side and still the switch will blink on then off. Any suggestions on what to check next? And yes, trying to route the passenger side harness out was a pain in the .

kcs:

Again, I would suggest first swapping the relay from the passenger side into the underside of the driver's seat as it is relatively quick and easy. That will eliminate the relay as a possible culprit.

From what you describe, it's possible there is a break in continuity outside of the seat heaters (i.e., in the wiring leading to and from the heaters and to and from the relay under each seat. Check the TSB that "jpflip" has listed in one of the posts above for the most likely sections to check because of the seats sliding back and forth and possibly damaging the wires.

If that does not do it, you can still try next to isolate the two parts of the seat heater (the seat part and the backrest part) and test for resistance with an Ohmeter as Saved4it has spelled out in the posts above. In your case this does not sound as likely because of the swap you did with no change in results, but it's worth repeating the tests. Once you find which of the two sections has no continuity, you will have identified the bad section (or the bad/chafed/damage wire section mentioned above) and then you can replace it.

Labor and care intensive, and time consuming but trust me when I tell you that it will beat the pants out of going to the dealer for this! .

Regards, Maurice.

[Dan Babb]

Dealing with this issue on the driver side of my 2004 911 cab.

Do you have to pull the seat to get to the relay? I'd like to test that first. Our dash light just barely flickers on, so I'm hoping it's just a bad relay.

[jpflip]

I don't see any relay in the wiring diagram for seat heating. Only a fuse A6 and a control unit located under the seat. You better do a resistance check of your back cushion and seat bottom...

Edited January 24, 2013 by jpflip

[1schoir]

Dan:

You don't have to remove the seat completely. You can just unbolt the four bolts holding the seat rails to the floorpan and then just TILT the seat back. That will expose the underside of the seat and give you enough access to get at the relay.

Note that if you pull the seat out and disconnect the wiring harness, you will set off the airbag light which then can only be reset with a PST2, PIWIS or Durametric.

Here are photos of what the relay looks like, and how it looks under the seat (this is from a Boxster, so yours may be a little different):

Regards, Maurice.

[Aleksander Nyland]

Nice write up, and valuable information!

I do have on question.

Would it be possible to just disconect the backrest heat? would this make the seat cushon heat work? or would this just provide an error code?

I do agree it's best to fix it so everything works as it should, but could this be done as a quick fix before one have time to do all the work with replacing the backrest heat?