Thanks for all the great information in this post. I have one question.

If I swap the good heater (passenger) side with the not working heater (driver's side), should it automatically work (assuming the back unit was the problem)? Or, will it not work without resetting the codes?

I don't have a code reader. I did the trouble shooting. My cooling works. My heat cuts off whether I only use the back or if I use the back and base.

I opened up the seat thanks to Tinribs's instructions. I pulled out the back unit. The only crack I could find looked like a hairline scratch, but when I pressed it down, I saw it was a small opening.

Yep! No need to clear codes, back heater units are identical.....just plug & play. 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
BMW R1200GS
Alfa Romeo Giulietta
Just one Montesa now, 349 White Wonder
Austin A40 Farina MK2
1975 Morris Marina 1.8TC

I moved the passenger seat heater to the driver’s seat, and it works now.

I thought it didn’t at first, because it took a while for the fans to make noise. With the broken heater, when I’d turn the heated seats on the base fan would make noise immediately and quit after a few seconds.

I’ll get a new one for the passenger next year. 2012 HSE 5.0 V8

Justin did you remove the seats or just the backs out of interest? I have the same issue, drivers broken passenger works. 2009 TDV8 3.6

lostinspace: Has yours got the heated/cooled seats, if not, I believe the set up is somewhat different.
I've just replaced my heater unit on the back of the front seat [from Duckworths] & just used the for & aft seat position.
The older seat may have different lugs/fasteners/clips etc etc.
Hope this helps. 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
BMW R1200GS
Alfa Romeo Giulietta
Just one Montesa now, 349 White Wonder
Austin A40 Farina MK2
1975 Morris Marina 1.8TC

Thanks yes 2009 (201o model year) with cooled/heated seats. The passenger works, the drivers whirrs for 10 seconds then cuts out sadly. 2009 TDV8 3.6

@lostinespace, the seats should be the same setup as the heater filters are meant to be swapped as a service item (but probably never get done!). No need to remove seat, just removal of the back panel. It takes about 40 minutes all-in, but can be a bit fiddly. Best thing to do is just take it slow and gentle, only fiddly thing I had was that the seat valance on the centre console side isn't held in with a tab, but is held in with a screw. If you take your time and do things gently you can get the panel off without removing the screw as the valance will flex enough to allow the panel to slide down and past with a bit of gentle persuasion.

@Justin, just had another look at my old heater ducting and found an identical split in my duct. It was virtually invisible until I pressed the duct at the exact same spot as in your photo and then the crack appeared. Strange thing is if I block off one end of the duct and blow down the other end I don't seem to get any air coming out of the split.

lostinespace wrote:

Justin did you remove the seats or just the backs out of interest? I have the same issue, drivers broken passenger works.

I did not remove the seats. I pushed them all the way forward and leaned the seat back as far forward as possible. Then, I sat in the luxury of the back seat while replacing the heater. It’s the most comfortable I’ve ever been doing a repair.  2012 HSE 5.0 V8

@Discotigger. It took me a while to see the split. It is amazing that something so small would make the thermistor fail (if that’s what happened).

It was nice having my heated seat driving to work and back. I have never had heated seats until now. I had it on the lowest setting, and it was almost too hot. 2012 HSE 5.0 V8

Another B1231-7A [Right seat fluid leak or seal failure]. fixed by replacing the seat back unit.

I replaced just the cell but all fixed and working now.

Hi JNC how much was the cell out of interest? Cheers 2009 TDV8 3.6

I could probably find out myself but does anyone know if you could replace the front seat back blower unit with one of the blower units from the rear seat base? I bet they are similar.

The front seat base heater unit differs from the front seat back heater unit so betcha that could be the same for the rear seats?
Why on earth JLR couldn't use the same unit for every seat, lord knows!  2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
BMW R1200GS
Alfa Romeo Giulietta
Just one Montesa now, 349 White Wonder
Austin A40 Farina MK2
1975 Morris Marina 1.8TC

Downhillerffrr wrote:

I could probably find out myself but does anyone know if you could replace the front seat back blower unit with one of the blower units from the rear seat base? I bet they are similar.