'Tis the season … to start using seat heaters, if you can get yours to work.
When I bought my '94 4.0 Superblue, the seat heaters did not work. Worse, what seemed like otherwise normal operation of their systems has gone even further south … I imagine, being originally a Mass. car, the seat heaters saw a lot of action in the cold winters up that way, even with only 80K miles on her. As to the passenger side heater, when I hit the button originally I could hear a relay click and the indicator light would come on (but of course the seat never actually heated up). Now, the light comes on but I no longer hear the relay click. As to the driver’s side seat, hitting the button originally would cause a faint relay click, but the indicator light would not illuminate (and no heat in the seat). Now, I’m not even getting the sound of the relay click, no matter how hard I press the button.
What’s the recommended troubleshooting path to follow on this issue? Problem is, if the actual heating elements in the seats are bad (particularly the driver’s) then I probably won’t do anything else with the system, in that it is my understanding it is a major PITA to r/r the seats, then r/r the cushion, and finally to r/r the heating elements. It’s also not likely I could find other seats in the color (Doeskin) with working heaters and in very good cosmetic condition.
First step for your scenario would be to access the connector under each seat; measure the resistance across the seat side wires. Should be around 2 ohms, if it is than you will know the elements are intact.
On my ‘88 it is a round connector. I had open circuits on both sides, a broken wire at the thermostat on the left, and an open thermostat on the right.
And you are correct that they are difficult to work on without damaging something.
ATTY Dallas - - Have never had anything warm up the seat in my 95 except the body heat of my big butt. Since south Alabama doesn’t have too much really cold weather, i have never been too concerned other than to assume if my car has them, they don’t work. If my car doesn’t have them and i decide to have them, I would go like Motorcarman and do after market.
For knowledge, According to the 1992 XJS Tech Update, Jaguar installed new seat heaters starting in 92 that used a closed loop temperature sensing system in addition to the timing function. The control unit employs field effect transistors to replace the previous relays. The system ensures faster warm-up and improved temperature stability. It also eliminates clicking noises associated with relays. The seat heaters operate only if the ignition is in position I or II.
Seat heater control unit is in front of each seat, and controls the heat timing and switching function.
The 94 XJS Tech update says seat heaters were optional in 94 XJS, standard in 94 XJS V12. And of course installed in both in the Cold Climate package for Canada market
the 95.75 XJS Tech update states the new heater elements have thermostats instead of thermistors to control temperature. STates the control module are 10-12 minute timer relays, installed on the left and right rear of the engine bulkhead instead of below the seats. On vehicles without the seat heaters, black protective covers are installed on the control module connectors of the bulkhead harness. Operation : When a seat heater is selected on, the related control module energizes and connects a 12V dc supply to the heater elements. The thermostats then regulate the supply to maintain the heater elements at a temperature of 32 to 35 degrees C.
After 10 to 12 minutes the control module automatically de-energizes and disconnects the
supply to the heater elements. The system then remains off until the seat heater is selected on
again. The control module also de-energizes if the seat heater is manually selected off before the 10
to 12 minutes time delay has elapsed.
BTW - - getting the seats in and out isn’t so bad. I recommend going to Harbor Freight (or some such and getting a movers pad/quilt) to put on garage floor to place the seat on when you wrangle it out of the car. Someone did a nice write-up on the forum about taking seats out.
In reply to a message from Jackdog1 sent Sat 10 Sep 2016:
Hi Richard,
I removed the drivers seat in my '94 last year and it was
pretty easy.
Just slide all the way forward and undo the to rear screws,
then slide all the way back and undo the two front. I found
the four nuts where captive/welded so there was no need to
pack anything in there to stop them rotating.
When you get the seat out it there was just one bolt either
side, which also double as the hinge pins to separate the
seat base from the back. And then unplug everything.
If you have the celebration seats with integrated headrest
that part may be different.
If you want to disconnect the runners from the seat base
that was just another four bolts but you’ll need a 12v
supply to power the runners forward and back to access those
four bolts once the seat is out of the car.
I had sourced a NOS seat base in doeskin so all I needed to
do was put it all back together in reverse and it gave the
seat a whole new life!–
1994 XJS 4.0 (AJ6) & 1964 Wolseley Hornet MKII
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Thanks for the info. and “options”, everybody (wow - Bob - I would think by 2001 MY Jag would have gotten the seat heater thing down reliably, btw) … One thing I have thought of, and maybe this is the easiest way to “untie the Gordian Knot”, is to just use a household heating pad that plugs into the cig. lighter, when the temps warrant. I wonder if anyone has come up with such a device … Only thing I would be concerned about is that it might draw so much current through the cig lighter as to blow the fuse … (?)
Only thing I would be concerned about is that it might draw so much current through the cig lighter as to blow the fuse … (?)