Good news: alarm siren works VERY well.
Bad news: it has developed a mind of its own!

My 1996 XJR has suddenly developed an erratic alarm, being set off without any prompting. In the two years that I've owned the car this has never happened. The only change I can account for is connecting a CTEK battery conditioner to the car: this was two days ago and the alarm problem manifested itself this morning. Unlocking/re-locking the car has no effect.

Has anyone else had this problem? Any ideas? All helpful suggestions gratefully received.

 

Hi Andy
Got the same problem on my S-Type.
Alarm triggers randomly, but not the usual alarm sound from the cars horn, it's a different higher pitch siren type alarm, and no flashing indicators either.
Is yours the "normal" alarm sound or a different one like mine?

steve

 

Without really having a working experience with this alarm system other then a hard reset to solve some lock sequencing issues I do have a suggestion for you as you can better manage the situation as a usable vehicle until you get to resolution . The alarm sounder is located behind the right headlights on the bottom of the mid level floor in that area . Just remove the connector for now . There is a history of water getting into this powerpack / horn unit which is if I recall electrically tied into the alternator voltage regulator and other devices . Will have to look at the prints for suggestions if this trips the horn other then a command from the Security ECU . This is a crude paint doc I made on a different topic as my Windows 10 is in limp mode without Works .

 

Thanks Lady P
I just finished a new post about it in the S Type general tech section.

steve

 

Hard Reboot is what you are referencing to ?

 

NO, the erratic alarm problem caused by the passive sounder seemingly failing.

 

Oh , I was hoping it was how to fix Windows 10 , not responding .

 

Unfortunately not.
Windows 7 quite possibly, but not win10.
Have you tried a restore to an earlier date? Before it started to pay up?

 

Have you checked the connector on the security ECU as mine was tie wrapped closed over in locked position . Most if not all ECU commands are grounds as the devices are ground seeking as a general rule . A loose connection meets that requirement and may be triggering the sounder unit . There are NiCad rechargeable batteries inside the sounder and I assume a normally powered open switch across the horn inside . As you lose the ECU wire ground in the sounder the switch closes and wakes the neighbors . The battery charging side of the unit is a passive discreet circuit and the switch across the horn is a active discreet . The ground symbol in the print is for the charging circuit . If you remove the battery connector and the sounder goes to silent it proves the sounder is working correctly and the fault lies elseware .