Good morning Everyone

After much searching and checking I am convinced that my security module is faulty
I have lost central locking, security light and radio, radio antenna, won't crank
Unfortunately I am unable to source a replacement
Does anyone know of an alternate supplier or of any way to bypass the module?

2/93 XJ40 3-2 ltr VIN SAJJFALG3A677585

Any advice greatly appreciated
Cheers
Ken

 

Hi Ken,

My first suspicion is that your Central Microprocessor (CPU) is the culprit. All of the functions you list are controlled by, or pass through the CPU, which is mounted on the firewall alongside the Climate Control Unit. On our LHD car, it was on the right or passenger side. Assuming yours is RHD, you may find yours to the left of the CCU. A common issue is that water can pool in the tray under the A/C evaporator when the drains become clogged with deteriorated foam rubber insulation inside the CCU. The water then sloshes over the edges of the tray onto the CPU, contaminating its electrical connectors and sometimes leaking into the CPU case and contaminating its circuit board.

It takes some disassembly to get to the CPU due to all of the components in the way, but my suggestion would be to gain access to the CPU and inspect its connectors for corrosion and if you find any, also open its case to inspect the circuit board. If you're lucky, cleaning the connectors may restore proper performance. If not, you may need to source a salvaged CPU from a similar year car. You can look up suitable part numbers at jaguarlandroverclassicparts.com. In the U.S., eBay is a good source for salvaged parts. I don't know if the same is true Down Under.

The inputs and outputs of the CPU are shown on the wiring diagram in the Electrical Guide, which you can download here:

Jaguar XJ40 Electrical Guide 1993-1994

The large images at Jag-Lovers have still not been transferred to the new servers, but you can see my thumbnails and descriptions of the CPU and surrounding components. Your car is probably a mirror image of mine.

The Brains Behind the Dash Underpanel

Cheers,

Don