Help needed-heated seats
 

Hello all:

I have this gut wrenching feeling I bought a lemon! I have just purchased a 2004 XJ8 VDP 4.2L w/38500 miles on it. Finding many problems that were hidden. Anyway, one of them is that the heated steering wheel gets plenty warm enough but all four seat heaters fail to warm up at all. I have checked so far that all fuse are good and that there is power to the switches. I have seen that others have had the same exact problem, but have I have not seen a reason or fix. Any help would be greatly appreciated and thank you in advance.

I felt the same way when I bought mine. The drivers heated seat didn't work in my old car, so I was real excited to get a hot bum again.

The fact is, the heated seats in these cars are generally garbage. They DO heat up, I promise, you just won't really notice it. If you concentrate real hard after driving for 15 minutes or so, the less clothes you have on the better, you may notice something.

Someone likened them to a 'gerbil breathing on you'. I think that really sums it up.

Do the little red indicator lights come on when you press the switch ?

The switch doesn't actually supply the seats with the electric current, it switches the circuit housed in the control module. I am not sure which module switches the seats, but it is probably the FEM. It is more than likely to be a bad connection somewhere. Sometimes the connection underneath the seats is found to be disconnected, or needs disconnect/reconnect to restore the supply.

The heat of the seats is related to the inside temperature of the car. If it's 70+ inside the car, the seats are not going to get warm (said in owner's manual). Try when it's 40 out and see if the results are the same. I can that on my VDP, all 4 seats heated as they should, but were not as fast or hot as my XK.

The steering wheel is overly heated compared to the seats on VDP, but I know later on Jaguar seperated the heated switches for the seats and wheel.

Fraser - thanks again for your input I really appreciate it. Yes, the 3 red lights come on for all 4 switches. I was planning next to remove the seats and check the connectors. I am not sure where or what the FEM is - could you please narrow it down for me. Thank you.

FEM=Front Electronic Module. Located at the base of the LH side A-post.
It controls the front heated seats.

The REM (Rear Electronic Module) controls the rear heated seats, (if fitted). Located on RH side of luggage compartment, behind the trim panel.

And by the way.............

There is a note in my Technical Notes (heated seats section), pointing out that they are designed to operate below a certain temperature, (doesn't say what this is !!), and says storage of vehicle in heated garage, bodyheat, and warm ambient temperature can inhibit the seat heaters.

Apparently the three heat settings equate to a controlled seat surface temperature of:

High - 42 DegC
Med - 37 DegC
Low - 35 DegC

so it doesn't heat up to much more than body temperature anyway.

Regardless of what the button LED shows, the seats may also get switched to the low setting if there is a high electrical load on the car.

My 1999 VDP does not have switches for heated seats, which I thought was very odd, what is the chance that the wiring is already there? I don't know what to look for.....

Last winter my heated seats were warm not hot. Looking around the net I found that Goldwing riders had the same problem and solved it by splicing a resistor inline with the sensor. Further looking I found

http://www.powerandsignal.com/images...HeaterApps.pdf

Describing a sensor used in OEM seat controllers.

This week while doing some other work I had the rear seat off and decided to measure the resistance of the sensor at various outside temperatures (early morning and late afternoon). Here are the resistance values and temperatures

55F - 7450 ohms
80F - 4630 ohms
85F - 3620 ohms

This matched well with the Amphenol sensor described in the above link.

Based on U102768 wrote (temperature of 35C, 37C and 42C or 95F, 98F and 107F) and using a chart for the Amphenol sensor I believe Jaguar is using, adding ~1K ohm resistor in series should make Low equal to the current High, Medium equal to High plus 10F, and High equal to High plus 20F.

I have not tried this yet but I plan on splicing ~1K ohm resistor in series with the sensor on the right side rear seat and compare how it feels compared to the left side rear seat if I turn them both on in the morning. I should be able to get this done by Friday and I'll report back then.

The seats in the 07 have better heat than the 04's do. Would jump both up if i could.

My 2004 needed both lower heat pads replacing last winter, while they had all the leather covers off they also replaced the backrest pads as well, it seemed well worth the extra cost of the two pads as the labour content was virtually exactly the same. Sod's law would have that the rear pads would pack up anytime soon and then the leather would have to come off a second time.

I'm new to the forum but the above reference to the switch panel and heated seats made me wonder if for economic reasons the heating elements are installed but just not connected. Same with the steering wheel heater. My car is a 2005 XJ8

Heated Seats
 

duplicate

No, or very little, heat from mine either. Having had a three-stage heating in my old SAAB, Warm/Hot/OWW, my X308's were a disappoinment. I was hoping for better in my X350 but more of the meh.

I added the resistor (see post #10) to both rear seats and now they are warm, toasty, hot rather than cold, cool, luke warm. Ihaven't had a chance to do the fronts. I hope to due them Thanksgiving weekend. If I do I'll try and do a write up afterwards.

Seat heater resistor
 

Have you/could you do the write up for adding the resistors to the seat heaters to improve heat levels? What resistors are required, ebay link would be great, along with where and how exactly these are fitted as wiring diagrams are like reading Japanese to me haha, any help with thus mod is greatly appreciated
kind regards
Mark

I second this request, thx

I did the rear seats and adding the 1K resistor in series with the thermo-sensor made the seats warmer. I never go around to doing the front since they have quit working do to a break in the heater. The need to disassemble the seat (remove the leather) is holding me up.