Hi all, I would appreciate a second opinion on my diagnosis thus far;

This is a 1997 XK8 Convertible. After successfully fixing the switchpack for forward/backward seat on the worm gears (and removing a facemask that jammed it,) I was working on the other issue, the squab. The condition is I get rotation backward on the squab via the switch, but forward does nothing. No power to the motor. I checked with an iCarSoft i930, and the passenger seat module shows no error codes.

Here is what I have checked so far:

- P/O and P/S (purple-orange, purple-slate) directly to the motor (PCM disconnected) will actuate the motor both directions for the squab. I was able to move fully and easily the full range whilst testing on the bench.
- Switch continuity was tested all the way to the pins on the switch, it operates without issue for both forward/backward squab buttons.
- Continuity from the switch harness to the PCM was verified harness-to-harness by probing the end connectors
- Inside the PCM, the pin which connects to the forward switch makes continuity to the PCB, and as far as I can follow the circuit (it gets lost under the harness plastic itself, after one or two hops on the board)
- I see no other broken solder or any other suspicious joints on the board

Since I've verified the squab motor works, and the PCM gets power to all controls except forward squab, it seems this must be some defect in the module itself. I am looking to get a second opinion before I pull the trigger on one of the units on Ebay, if someone has the time to look this over.

Thank you!

 

Swap in the Driver's seat module to Passenger and see if that helps.
Set the seat where you want it, then put it back in the Driver's seat.

Send the Passenger out for repair.

 

This confirmed the module. I went ahead and ordered a used one, but I can't help myself, and I've taken the bad one apart to diagnose further.

So, I found five relays inside. The farthest, lined up with the P/O P/S lines that go to the squab motor, tests good by applying voltage to the correct pins as shown in the schematic diagram:


Five relays shown here; the bottom-most one goes to the squab

Relays found in XK8 seat modules (x5 per module) These activate the heavy gauge wires which go to the squab f/r, seat f/r, seat up/down, lumbar pump, heated seat

The underside pins as they relate to the diagram; each relay can be tested by applying voltage to each small pin pair.

The relays at rest maintain continuity with one side of the pole & thus remain in a "shut off" state. Depending on which side of the relay is activated, it will switch +/- polarity across the heavy gauge wire pair thus actuating forward / reverse for each component controlled by each relay.

I can actuate the relay for the squab using external +12v and observe it operating normally, bypassing the module wiring. (For bench testing, in addition to the audible "click" I can confirm continuity between the expected heavy-gauge poles when doing the test.)

Where I get lost is what interrupts between the harness and relay actuation (small) pins exist - it must be a control built into the on-board chip (shown in the earlier photo.) I get odd resistances across everything, indicating to the best of my understanding that it must all be going thru that chip. Tracing can only go so far, and I'm beginning to wonder if this could actually be a programming issue, not a circuitry issue.

EDIT: Another reason I suspect programming and not circuitry, is I get same resistances from both of the harness control pins for the squab (G/Y, G/W) to the relay control pins.

 

I've found copper traces disintegrated and/or worn from case contact. Check the outer traces.

I have installed 'jumper wires' to get them working again.

 

I could find no damage, and resistance measurements seem consistent across the pin that doesn't work, with the ones that do work, following to the control pins on the relays.

I have IDS 118.5 set up, thinking to try reconfiguration of this seat module. However, the only option it seems to give is for programming the ECU. This is the very first time I've started IDS, for what it's worth.




Am I incorrect, that 118.5 IDS can reprogram a seat module for this 1997 XK8 convertible?

 

The VCATS label in the boot has the module part number and suffix and the software is already configured for the module.
There was a TECH TIP in 2004 for configuring 2001/2002 MY seat modules and I actually had to do this once.
Luckily I worked at the dealer and just found a later car to perform the configuration.(I don't know how I remember these things after so many years)

"Models – XK8/XKR 2001/2002 MY
Symptom: PECUS D or PECUS P warning after replacing seat modules
Information: After replacing one or both seat modules, a technician will see a PECUS message on the dash. When looking on the WDS, there will be no programming option for the seat modules. To repair a tech must locate a 2003-04 XK, install the seat module in that vehicle, and then program with WDS. The only side that can be programmed is the driver's side; therefore a passenger seat module must be placed in the driver's position and programmed. After programming install modules in original car, PECUS message should be gone."

There is NO OPTION for the 4.0 cars BUT it IS an option for the 4.2 cars!

IDS (or WDS) WILL be able to perform the configuration IF you can locate a 4.2 liter X100 and get permission from the owner to plug the modules in for configuration.

GOOD LUCK and let us know how you make out.

 

Same here. Cheap and easy fix. For me it was the very outer track. It looked fine but when I checked with my meter it was broken somewhere.

 

... This is it.

The outer track goes to the squab forward circuit. The one just next to it goes to the squab back circuit. I expect a squab failure to be the most common thing, and this repair takes care of the issue.

See here, close inspection shows some breaks that I had missed:


As it turns out, the actual break was on the corner / bend just above the last relay, not what looks like the suspect breaks in the middle.

Soldering against a trace is something I have never attempted before; and these are very tiny. This took me a long time to get just right, using high powered reading glasses, a razor blade, and LOTS of patience:


I scraped the trace to expose the copper, and then a needle-tipped iron. Still ended up with quite the gob of solder, but it works.

I traced continuity to the wire to confirm, and double-checked that I had not created a short against the other nearby circuits, before securing everything.


The reverse side, where it meets the pin.

I decided to protect the whole back side from further chafing inside the case.

Just tested, and now the squab works as expected. I hope this helps someone who might encounter this issue, as I think it is probably quite common in these seat modules. Even if you don't have this issue, I highly recommend putting a strip of tape to prevent this, if you ever have cause to remove the seat for some reason.

Thanks again to all the forum members for your help!

 

Great you got it fixed! I find these sort of repairs give great satisfaction. The headrests fall into this catagory too.