XJ40 security system information

Hello all …

Last week my key fob stopped operating the door unlocking and security arming. Replaced the small battery but still wouldn’t work. So my investigation began !

I have a 1989 model which came equipped with the infrared (IR) door lock system. This consisted of a small plastic half bubble receiver on the overhead console and via a very basic key fob commanded the central door lock module to open or close all 4 doors, the trunk, and the fuel filler door. That was it, there was no security system.

Screenshot 2024-02-09 at 1.16.37 PM

Screenshot 2024-02-09 at 1.18.30 PM

Around '93 or '94 I took my car to the Jaguar dealership to have them install a security system that was now available with the later models.

The blue arrow is the XJ40 security module. The red arrow shows the housing for the backup 6v battery for the security system. This is the battery that most people don’t even know (or believe) actually exists (more like an urban legend). Personally this is the first time in 30 years I’ve even seen one. This has a sticker attached that says “Specific cruise control inc.”. I can only image this is a hail Mary attempt to deter any miscreants :grinning:.

The left key fob is the one Jaguar provided me for the system. It has 8 dip switches and operates at 310 mhz frequency. Sure enough when I opened up the security module it also had 8 dip switches (with the same settings as the fob) buried deeply among the two BIG printed circuit boards.

As you can see I ended up with two remotes that look exactly alike. The remote on the left is what Jaguar provided me with when they installed the system. Strangely enough it is an exactly match to the Linear “lady Bug” miniature garage door opener remote. So I purchased one many years ago to use as a spare and after setting in the 8 dip switch code … it never worked !! If you blow up the picture you can see it appears to be a lot more electronically complicated than the one on I had. Another head scratcher is that even though they both transmit at 310 mhz it didn’t work …

… and speaking of frequencies last week I purchased a neat bit of kit for around $25, It very accurately reads the frequencies that remotes are transmitting at …

I’m not actually sure what your query is, but the alarm module, with 8 dip switches, looks like a Foxguard alarm module.
They were pretty cheap and nasty, but popular.

Those Keikert IR modules are generally reliable, check the IR output by facing it at a digital camera while activating the button.
The most common reason for failure on those is cracked solder joints at the LED.

If anyone has spare Keikert IR transmitters and receiver pairs they don’t want, I might have a home for those.
On my Citroens I have one with an unmatched pair, so might be able to repurpose a Jaguar one.
AFAIK, there is no simple way to reprogram these, only matched pairs will work.

Hello there Dieselman …

No query, just thought I’d share some information on a system that is rarely (if ever) discussed on the forum.

Interesting. I always remove any vintage alarms on my cars because they can be any source of problems. My xj was equipped with the IR remote, but the previous owner told me that it stopped working 10 years ago , he told me that also che illuminated key, used to work when the car was young but then it failed.
My first operation was to change the batteries and both start working again. Maybe jaguar failed to tell the owner that there where more batteries in the car system than the engine one.