VEHICLE: 2000 XJR

This just happened: All functions on my powered driver's seat work except the ability to lean the seat forward... I tested that the motor that reclines the seat works but I can't get it to un-recline the seat to an upright position.

I think the switch is fine because I jiggled it and it feels fine. Also (and this is really important): I had three memory settings for that seat and even recalling any of those memorized positions does not change the reclined position of the seat back. That's why I believe that either the motor that elevates the seat back is broken (or is it the same motor that reclines the seat?) or that the seat module circuitry has lost its ability to communicate (i.e., supply power) to the motor in order to move the seat to an upright position.

I understand that the fault is likely in the seat control module and that I can test by swapping it with the passenger's side (which works perfectly). But before I do that:

1) Is there a separate fuse that is needed to enable the seat back to be moved back into an upright position?

2) Are there any good instructions that would help me do what I need to do to access and/or swap the seat control module?

Thank you!

 

It is likely a corroded trace on the module circuit board, and there ia not a separate fuse.

I don't know about removing the module in the sedan, but the XK8 has two nuts that are loosened and the the module can be slipped out and disconnected. As in any module work, disconnect the neg. battery cable first.

There is a repair service for the module, or at least was a couple of years ago. Link below.

https://www.jaguarforums.com/forum/x...dation-103908/

 

I'm an EE, no need to use a repair service. However, I don't know how to do the mechanical stuff, like removing the module, etc. I'm rather sure that it will be the same in the XJR as it is in the XJ8, so I will take a look. I will try to remove only the module (I do hope it's possible without removing the seat).

Thanks, and I'll keep this forum posted. If anyone else wants to chime in on how to remove the module and whether it's necessary to remove the seat, please do so. I will be out there looking now, but will check back soon.

 

OK, I had to remove the seat because the seat control module is mounted to the underside of the seat cushion. It's possible to remove all four retaining screws on the track of the seat and then lean the seat back, but because my seat angle currently is >90 degrees, that was difficult. So I detached the SCM cables and then removed the seat from the car.

Now I'm going to swap the module from the driver's side to the passenger's side (I expect they're the same but perhaps the driver's side SCM holds the 3 memory positions too). If they are, then at least I will be able to drive the car and service the passenger's side later.

I looked at the circuit board and there are some odd oxidation marks here and there. I don't know if that's the root cause or if one of the relays is bad. Either way, I may try to order a new board once I confirm the the SCM is indeed the issue (versus, say, the control switch or the wiring).

While everything is apart, I'm cleaning all contacts with contact cleaner and a Q-Tip.

Regards,
Allan

 

Holding the two SCMs side-by-side, it appears that they're the same. The driver's side seems to have an extra connector in the middle, but the SCM part numbers are the same. That cable probably feels the seat-memory selection.

By the way, the passenger's side SCM has no visible "oxidation" marks on the circuit board... The plot thickens.

Gotta run out for an appointment but I'll post the results of the SCM swap hopefully later today/tonight.

 

I have had this problem on both my XJ8 and my XK8 a careful examination after opening the module will reveal cracks on the outer copper trace. Which by the way is seat tilt. You have to solder in a jumper to bypass the cracked trace. I had Darrel do my second one cheap at twice the price and as of 2 months ago he is still going strong.

 

Avern1,

Excellent--thank you.

Crazy, isn't it? I know 15 years is a "long time", but is it really? Shouldn't PCB traces not crack? I can only wonder how Jaguar and other manufacturers try to improve on their newer products knowing what learn from older ones. For instance, if I were the QA lead at Jaguar, I would insist that PCB traces be thicker and more resilient to heat--perhaps even coated as some motherboard PCBs are.

In any case, thanks for the tip. I will do some continuity checks on the traces and add jumpers where necessary. If I had a schematic, I think I'd be able to identify the tilt trace(s) and focus on only those.

Not to take anything away from Darrel (I'm so thankful there are guys out there like him!), but I like to learn and do myself.

Finally, I have good news: The passenger-side SCM works perfectly in the driver's side! I did the swap--but I also had cleaned all of the connectors. They didn't seem dirty to the naked eye, but I don't yet know for sure whether it was the SCM swap or the cleaning of the connectors (or possibly both).

Meanwhile, I have the original driver's side SCM out and on my desk. I will work on that tonight and will finish the job tomorrow.

(By the way, those seats are really heavy!)

Allan

 

You think that ones heavy, I had to wrestle the seat out of my x-type to change out the seat belt buckle. They are large and soft and heated but real @##$ heavy. Visually you should be able to see the cracks in the traces. The circuit board is mounted such that it gets a lot of vibration and bouncing around in the case. There is also not much distance from the traces to the edge of the board.
Good luck and good motoring.

 

OK, I finished the repairs All seat functions now are working again.

I found the solution here:
https://www.jaguarforums.com/forum/x...g-else-130069/

I would have preferred creating a more professional jumper than the one depicted in the link above (perhaps by dropping the jumper into a drill hit)--but I ended up CAREFULLY scraping the coating from the damaged trace and soldering directly to the exposed trace itself...

I couldn't believe that there would be broken/corroded traces on the PCB--but there were! Oddly, the SCM damage happened only to the driver's-side module.

Regards,
Allan