www.jec.org.uk

after going out to the car yesterday evening, the central locking wouldn't work, and the alarm was throwing 50 fits

after calming the alarm down ( pulled the backup battery ) and getting into the car it wont start

symptoms ,

no remote control
no central locking,
no puddle lamps
no interior lamps
no gear release solenoid
no dash panic locking button
NO START

after much investigation and head scratching, i managed to start the car by physically making the starter contact in one of the modules under the passenger dash , yes, i had to take it to bits to do this !! but the car starts every time but still none of the above functions
and pressing the brake pedal will not release the gear selector,

i have discovered that the central microprocessor control unit handles all of these systems , and from the schematics it seems that it has a direct feed from the ignition switch , this could be a supply or ground to the module, or the module is fubar in some way , or could be ( if I'm really lucky ) a connector that isn't quite seated, but the sunlight faded before i could establish this

wish me luck

BB

Does sound like its died a death.
It's located under the passenger knee bolster panel.
Check for any evidence of damp/ water in the Footwells too.
Especially around the fuseboxes.

I have a spare microprocessor if needed.

Thanks Naki

dry as a bone in there, ( fortunately/luckily ) ,

i started in the wrong place checking all the microswitches around the brake pedal and by the gear selector, even suspected the linear switch located next to the gear selector, but as the other systems have been effected i ended up thinking the central module was at fault, i will check the feed on "25" from the ignition

i really am hoping that its a loose connection from one of the plugs, but as we all know,......its a Jag , lol

thanks for the offer on the module, its a mid '94 car , with security system ,
what sort of money , as i have put a bid on one on ebay already , lol

cheerz

BB

good news

after obtaining a matching used central processor unit, and ensuring the battery was disconnected, i was grounded, the processor was grounded and had my lucky pants on i plugged in the replacement unit, ensured everything was seated correctly and reconnected the battery

instantly i saw the interior lights and puddle lights were working , and turned the car over on the ignition, she started without hesitation

so a right result

Thanks to Naki for offering up a replacement part, but i had already bid on one on ebay , which went very cheaply and the seller posted it out asap for me


but i think i may get a spare as well , lol

BB

Result!!
Well done.

Rare to get a quick fix but as so many services went fubar, it would indeed suggest module failure. The problem with diagnostics is as always finding out which services link to a particular module. That in itself can be a considerable time eater. Once the fault is itemized to a component, one always wonders how patently obvious the issue was and why you didn`t think of the reason immediately. I had that with my nineteen day glitch!

Well done, Mate.

Mike .

A 'well done' from me too. Central processor faults are rare on the XJ40, so far as I know.

the large hanging down central processor unit with its three plugs, its mounted on a spring clip behind the rail of three smaller relay modules that you have to remove to get proper access

IMG_1936 by MyPix on Talk Photography

one job at a time , lol

BB

and the 20p coin is for turning the plastic stud fasteners, as screwdrivers are to ' sharp ' and chew up the plastic, a coin is just right and i always have one in any car for such fixings, lol

BB

this is the central processor unit with no clothes on........i had to see if a component or track had failed, but nothing obvious, so i must conclude it was an actual chip that has failed ,

IMG_1941 by MyPix on Talk Photography

BB

I instantly saw the fault with that circuit board.

It says made in UK

show mw a desktop PC made in 1993 that is still going ? lol

BB