have a 2003 jag xj8, the "check rear lights" message was staying on, took it to a jag mechanic, said parts weren't available to fix it so he "wired around it". now the warning message comes on when you step on the brakes but goes out when you let off the brakes. Don't know what was down to wire around it. Have a friend who is a retired mechanic trying to help me fix it, but we don't know how it was wired around. Any one have any ideas.

 

Possibly an added earth (ground) wire was fitted to the bulb holder assy?
I had to do this to several of my sedans as well as customer cars.
The bulbs are also important to draw the correct current through the monitor circuit.
X100s suffer the same fault so I often see a separate wire added to the bulb board and lamp mount bolt to the body.

 

Motorcarman nailed it with his experience as the monitor is looking for a bulb circuit current range not being too high ( wrong bulb ) or too low ( burnt or wrong bulb or lacking / corroded ground path )

easiest thing is to try replacing the suspected bulb with the correct #

Cool drawing but may not need to go that deep

 

Motorcarman hint is worth checking, my cheapo bulb was throwing intermittent error till got swapped with the mainstream brand

 

I'm having the identical problem on my 2002, Thx fellas

 

On a past XJ8 the feed to one bulb from the module was dead. (Each bulb has its own feed). I tapped into the other side so it ran both bulbs. Since this would double the current and possibly burn out the module, I replaced the bulbs with LEDs. Since 2 LEDs draw less than I incandescent bulb I still got the warning message. I could have added a resistor to make the message disappear but never got around to it.

 

Years ago, Robert Spinner (RobertDIY.com) posted a video on how to wire around Jag rear brake lights to bypass SLCM control (that which sends you the message). From failing memory, 12 years ago, he wired the upper brake light (under the rear window), into the main brake lights. Later, he retracted it as it was a bad fix. Better to grab the exact VCAT for your SLCM and search for a used on EBay . . . there are companies that can also repair your SLCM (and Youtubes for doing it yourself).

 

I had that problem on one of my cars. It was the Security and locking module which is located under the trunk fuse box. The car had gotten water in the trunk through a hole in the rubber gasket fitting around the gas tank filler neck. ( It was one of the many problems with that particular car when I purchased it.)
The warning would illuminate when I pressed the brake pedal.

 

so what does SLCM stand for and what is VCAT

 

Security, Locking Control module; Vehicle Control and Test System. See attached.

In the left hand corner of your boot, pull back the carpet and you will see a tag with the appropriate numbers for your vehicle.

As Dave mentioned, it is too often a bad SLCM that causes the brake warning: using an elelctrical diagram, I traced each circuit, changed bulbs, bypassed the circuit, but got the same response you get every time I braked. A different SLCM (under the trunk/boot fuse box), fixed it. That was ten years ago. They are getting harder to find. But I see some for sale on Ebay.