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Discussion Starter #1
There are many posts on this forum about the SZ seat ECU issue. I’ve spent a number of hours perusing these posts but couldn’t find an answer to my particular problem. Maybe it is out there somewhere, but I couldn’t find it. I learned a lot of good info along the way, but unfortunately nothing relevant to my specific dilemma – so I’m reluctantly initiating another discussion. (I posted this thread two days back and it disappeared after I added some photos, so I'm trying again.)

Both door mirrors and the driver’s seat stopped responding to their control switches on my 1993 Brooklands. (The passenger’s set works fine.) I just noticed this this week as the car has seen very little use this season (Covid) and as the sole driver, I did not have to adjust either since I bought the car some years back. As per many posts on this forum, this implies a dead battery in the driver’s seat ECU or other ECU failure. TSD 4701 Electrical Manual 1987-88, section 27 Memory Seats and Door Mirrors – Manual Operation, etc. describes how to bypass the driver’s seat module. The procedure and diagram from there have been displayed and discussed at length here many times.

Unfortunately, the 1993 Brooklands has the later light-coloured (gray?), not brown, module. The wiring harness is substantially different than on the earlier cars covered by the ‘bypass’ procedure. It isn’t possible to simply reconnect ‘five-way’ and ‘nine-way’ connectors of the stowage bin loom on a 1993 car. There are completely different connectors with different number of wires on the 1993 loom.

To make things even more interesting, I opened my ECU and the battery looked fine. There was no leaking acid or visible damage to the board. The car was meticulously maintained under previous ownership (have records), so faults were addressed promptly and batteries were changed in time. When I put a voltmeter across the battery and even across the contacts on the other side of the circuit board – just to check connectivity, it gave a healthy 3.63V (rating is 3.6V). However, there could be another defect in the ECU.

I’m not concerned about the memory function, but I’d like to get the driver’s seat and mirrors working. To diagnose the overall problem (maybe it's not a defective ECU; fuses are all fine), it seems logical to bypass the most complex part - the ECU. Has anyone done a bypass of the 1993-era ECU to get basic seat and mirror operation? In other words, is it even possible to bypass /delete the memory ECU and if yes, has anyone done this and could they provide some advice? Any direction would be most appreciated – even the bad news if the bypass/deletion is impossible. (Would save me a lot of time trying to figure out how to do this.) Thanks!
 

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Discussion Starter #3
Exchange the front passenger side seat ECU with the driver's side. Both parts are the same. If the ECU is at fault then your mirrors will start to function.
Thanks JR2! Great idea! I assumed the passenger's side was a simplified version with no mirror control circuit, so this never even occurred to me. I'll give this a shot and will post what happened.

Incidentally, are the older brown ECUs the same as the newer ones? Except for the different connectors of course. I have a spare set of those from my 1989 parts car, but those are unfortunately north of the US-Canada border.
 

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Discussion Starter #6
Thank you - again! I didn't get to the car today, but I'll post what happened when I swap the ECUs.
As per JR2’s advice, I swapped over the ECUs. YES! This experiment proved successful! The module from the passenger’s side worked. Both the driver’s seat and the outside mirrors now worked. Thanks JR2!

I then connected the former driver’s ECU to the passenger’s seat hoping that it might work there. (Perhaps just a bad connection in its former location.) NO! The result was the same as on the driver’s side – no response from the seat. That ECU is dead, even though the battery is still good (3.63V) and has not leaked out so there’s no visible damage to the circuit board.

Unfortunately, this means I now can’t adjust the passenger’s seat as I don’t have a second working ECU. Repairing or sending the defective ECU out for repair is currently impossible as I will shortly be relocating back up north for the summer and the car will sit here for 6 months, hence there’s no time to do either.

So I’m back to a slight modification to my original question – is there some ‘quick’ way to bypass the passenger’s seat control ECU?

Yes, I realize that finding the right circuit diagram for my car (can’t find a complete workshop manual for a 1993 on the web, like I did for the 1981 and 1988) and making up some ‘adaptor’ harness would likely work. Unfortunately, I don’t have the time to do this exploratory work before leaving here, so I was hoping someone might have already done this and something might be available for a 1993 – like Bill Fane’s for the 1989 seat ECU bypass.
 

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So I’m back to a slight modification to my original question – is there some ‘quick’ way to bypass the passenger’s seat control ECU?
Sadly no. My battery had leaked on the driver's side and hence the swap.

There does not appear to be an easy way to bypass it.

I'm sure that the bypass can be done, but the effort involved strips the benefit(s).
 

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Discussion Starter #8
Sadly no. My battery had leaked on the driver's side and hence the swap.

There does not appear to be an easy way to bypass it.

I'm sure that the bypass can be done, but the effort involved strips the benefit(s).
Understood and thanks again for the earlier info. Hm, it almost sounds like a worthwhile project to figure out a bypass. But I guess other issues will pop up that will use up any extra time. ;-) This is where the early SZ cars have the edge - no ECUs and just simple wiring directly to switches.
 

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Discussion Starter #11
And by-passable ECU, when fitted, by simply connecting a few plugs together and plugging a relay in the pre-installed socket.
FLYER34 - Unfortunately this is not possible on the 1993 (and later?) cars as noted in my 'starter' post. The 1993s already have a relay there but they also have different connectors than the earlier cars. The car-harness-side connectors cannot be simply plugged into each other when the ECU is removed. Apparently this is possible on the earlier models, although I haven't tried this myself. I'll attach a few photos of the seat mechanism and harness from different year cars that I happened to have around of my and a friend's cars. Other than the 1993, we weren't looking at bypassing the ECU. (I just take photos of everything. :) ) The simplest is the 1981 that didn't yet use a memory or control module. The 1988 and 1989 cars have the brown ECU and the 1993 has the lighter-colored gray ECU. As JR2 notes, these are not substitutable.

Incidentally, on my email notice of updates to this discussion, I see Vertical Scope from Toronto as the sender. Is this RR Forum based out of Toronto? Hm, just like the alternative to YouTube - Rumble - is also based there and hence 'down the street' from me! :)

1981-8669a.JPG 1988-8553a.JPG 1989-9433a.JPG 1993-3978a.JPG
 

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Discussion Starter #12
Hi make sure all the relays on the ECU are free and clean, one was stuck on mine and stopped any movement.
Mike
Thanks mikebentleyturbo2 - That's something I'll do when I get back here in the Fall. Hopefully the north border will be open by then......though I'm not holding my breath! Arizona is fully open today but Ontario (Toronto) is about as locked down as can be.
 
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