Ok so my driver’s seat heater has never worked when I hit the button since I bought it, and the previous owner said it didn’t work for him either. I did pull the seat cover enough to check and yes, I am getting power to the heater when I push the button, but it doesn’t heat. However, oddly l have noticed that on really cold mornings, the seat heater definitely cuts on and starts warming up, then cuts off. It seems to do it automatically without me pushing the button! Is there supposed to be an automatic seat heating setting for when it’s bitter cold? And what would cause it to work without the button, but not with the button even when getting power?

 

Hey when you get a chance google: "Jaguar seat heater xk8".

Lots of info, most of which is from us at this forum.

FWIW once in a while mine turn off for no apparent reason. Button turns s back on in that case.
John

 

Oh believe me I did that search numerous times. Lots of good info, but admittedly I haven't searched in the last few months. I don't remember any posts about the seats coming on automatically without pushing the button. I had figured that more than likely I had a break in one of the wires, but when I did my test and got 12 volt I figured it was a break in the pad itself. I also saw where someone replaced the thermostat with a standard fuse and had thought of doing that, but it looked like mine was built into the pad itself. So I didn't know if Jaguar had changed the style of pads at some point

 

Have you tried to swap the seat modules? The standard issue is with the control module circuit board. See if the problem "moves" with the module swap. How is the heated seat red light on the button? It typically does not work when the module fails. The good news is that these modules are generally fixable by soldering shunt wires for the outer tracks that have worn out by rubbing on the hard plastic shell. This is assuming you have original parts the car computer recognizes and not some random module from another car, or even hacked wiring by a rushed owner on a budget. Also, check the module circuit board in case they are already fixed, but incorrectly, which leaves those heaters on all the time. The modules are under the front edge of each seat, fairly easy to reach. 2x10mm screws and 2 or 3 connectors in the back. Then the lid comes off by prying some tabs.

Best of luck, keep us posted.

 

Ok, I should have known :-).

looks to me like there are 2 issues:
1) if 12v is present - why do you get swinging heat? [Loose / bad connection?]
2) how can there be 12v if switch is unlit? [Notice I didn't say off, we've all seen some level of intermittent LED lighting with these switches. Guess you'll maybe have to verify the switch opens the circuit between it and the BPM or whatever controls the 12v]

I'm going to go look at the diagram to see if I can help you. FWIW I'd swear I remember seeing a note in my owners manual stating the seat temperature is limited by the temp in the climate control display, and I'm sure we really felt warmer seats with display raised to 80+ degrees in sub freezing weather (I'll put the roof downs much as I can), but as I recall there's no bloody temp sensor in the seat heater circuit to really support either of those statements.

We'll figure it out mate.

John

 

Drivers side seat has memory

Picture is not allowing me to type outside so:
seat heater on button sends ground to console control module. Led light is independently lit.
console module sends signal to BPM, which energizes a wire directly into seat heater. Seat heater seems to contain thermal safety breaker.
squab heater is wired in series with seat heater. (So if either opens, no heat that seat)
Squab sends end of circuit to a shared ground. This specific ground point is relabeled in cars with no memory, but concept is same.

If you are measuring 12v at incoming wire to seat heater = you must have an open to ground. Defective thermal?
I'd see if I could bypass seat heater and send the 12volts directly to squab.
Squab heats? = open seat heater.

maybe a better easier idea: open the wire into the seat. Measure resistance seat heater wire to to ground.
open? Find the break
Got a reading? Do same measurement on passenger side. They should be equal.

Re: the phantom on signal guess you have to figure out if defective switch (always on), short to console module (wire grounding), or defective console signal to BPM

 

I only get 12 volt at the connector when I push the button on the dash. When I do push it the red light comes on and then when I push it again it goes out. However even with that, I feel no heat in the seat. I only get the heat when it's at or below freezing and I don't push the button. I usually keep my temperature on my heater set at 72. I had also read that the seats were somehow tied into the climate control temp, but I never saw anything about them cutting on automatically without the button being pressed. As for what wiring has been messed with before I got it, I don't know. I had considered swapping the seat controllers, but I thought they had to be reprogrammed if you did. Also, seeing as how it showed 12 volt at the connector when I pressed the button, I figured it's probably not the controller.

 

https://www.jaguarforums.com/forum/x...-solved-44965/

This was the one I was thinking of, but my thermostat seemed to be hardwired in. Maybe I need to look at it again

 

We pushed post at same time:-). Let me know what you think

BTW that's a great link for this subject.

 

Makes sense! I'll try looking into it some. Although I have sinus surgery tomorrow so I don't know when exactly I'll get to "really" work on it

 

I just looked and mine is riveted and soldered to the heating pad. Drrrrrrrrrr

 

Ouch! Hey can you get to the leads? See if its open.

 

Ok so I went out and checked the wires on top of the thermocouple or thermostat, whichever it actually is, and with the car off it was reading 4.5ohm. when I started the car it showed 2.8ohm. I then pushed the seat heater button and it stayed at 2.8. I thought I'd try turning on the cabin heat to see if it did anything, but it didn't change. Not sure why it would drop when I just started the car, could just be operator error. I double checked voltage and with the button off the wires on too read zero. Button on and they both read 14.1v. No felt heat, but it is almost 55 today, so shorts and flip flops weather lol. The black wire from the input cable and the red wire from the top of the thermocouple just look like they have the solderedtips soldered and then glued to the heater pad. Part of me is tempted to cut out the thermocouple as was said in the one post, to see what it does

 

Don't bother bypassing it yet if you see volts on both sides. You then have an open between the thermocouple and ground.

From the schematic it could be in the seat heater or squab heater or connection wires. Can you find the wire between the 2 heaters?

 

T, good luck tomorrow. Let us know how you are.

John

 

Surgery went well. Not a lot of real pain or massive bleeding. Downfall is I have to sit and sleep at at least a 30deg angle for the first several days and nights. Also Im not supposed to bend over with my head below my heart. I guess I'll have to wait to look into the seat more