1998 XJR. The car does not seem to know that the seatbelt is fastened. It blinks the lights and sounds an audible warning as I'm driving. This is dangerous because the car briefly turns the lights off at night. Any ideas on what to check? Thank you.

 

It seems from the information that you have 2 different problems. Let's work with the seat belt first. When you say the car doesn't recognize it I assume you mean the seat belt light is on even though you are buckled. If that is correct then we need the trouble codes to figure out what sensor is bad or where the problem is. Get in buckle up and start the vehicle. Observe the seat belt light it should begin to flash. it will flash stop for 2 or 3 seconds and flash again. It should do that 3 times and then stay illuminated. You need to count the number of times it flashes each time. Say it flashes 5 times then stops for a couple seconds and then flashes 3 times. Your code problem will be 53.

Now for the headlight/horn problem. They are in NO way connected to anything going on with the seat belts. The circuits are separate and the lights.horn are controlled by the Body Processor Module. You will need to disconnect the battery and unplug the module and thoroughly clean the plugs. Next you will want to remove clean and exam the body ground strap beneath the car behind the passenger side front tire. Once all that's done give us an update and we can go from there.

If you would like to send me a private message wiht your email address I can send you the tech manuals pages for locating all of this.

 

Very helpful thank you. After reading your reply, I may have a grounding issue. The seatbelt indicator illuminates when the key is turned on. After a few seconds it extinguishes. Same if the car is started. Later the indicator will come on and chime, whether the seatbelt is fastened or not, then will extinguish after a few seconds. If the headlights are on, the headlights will also flash off and on at this same instant, which is why I thought it was a belt minder issue. I now think it might be a ground issue. I will try to work on it this week and will report my findings. I may need help locating the ground strap you mentioned but I'll look at it first.

 

New information for you: I checked the ground strap and all relays I could find. Everything seems clean and snug. Paying closer attention, I notice a barely perceptible click-click in the instrument panel when this happens, like a relay clicking in and out, or rather, out and in. Only two things happen at this instant, the belt minder dings a few times and the headlights blink off and on. Nothing else seems to lose consciousness. The engine doesn't cut out, the cruise does not disengage, the radio does not cut out, dash lights do not blink. Only the headlights and belt minder seem to be affected. Any ideas? Is there a relay in or behind the instrument panel? What other single item could affect only those two items? Can a diagnostic hookup at Jaguar detect these things? Thanks again!

 

More info: in the trunk next to the battery is what looks like a main wiring loom going from the relay box forward. There is a white wire with a blue stripe and a female spade connector laying there not connected to anything. I don't see a male spade connector anyplace in reach of this wire. The wire appears to be part of the loom, it runs along with all the other wires, but then lays there not connected. Any idea what this is? Hoping it's a ground that needs to hook to the ground bolt to a long missing male spade...

 

Yet more info: research reveals that the white/blue wire had to do with the transit isolation device and should not be connected to anything. Back to square one on the belt minder dinging and the headlights cutting out. Anyone? Thanks again

 

It could be a faulty switch in the seatbelt receiver, or the wiring. The clicking sound from the dash might be the signal to the warning light.
The WDS/IDS factory software will monitor safety devices via the can-bus so a dealer scan will find it but be aware of the cost involved in taking it there...

Wiggle the belt while fastened and ignition on, can you force a fault? Next would be to take the seat out to inspect the wiring to the receiver. The seat is held down with 4x torx bolts at each runner corner. A couple of wiring connections under the seat also.

 

I think I have solved this problem. It was the inertia switch.

On a whim I called a Jaguar dealer in Denver, with little or no expectation of success. I was pleasantly surprised when a technician returned my call, and he seemed very patient and knowledgeable. I described the symptoms and he suggested the inertia switch. He said the inertia switch can cause strange symptoms if it is partially faulty. The switch sends a signal to the system to disable the fuel pump and other things during an accident, to help prevent a fire.

I found a used switch on eBay and installed it myself. Since doing that, I have not encountered the problem. When I pulled out the old switch, it had a noticeable rattle compared to the new switch, even when the reset button was engaged. It may have been sending a fault message for a brief millisecond once in a while, causing the symptoms I was seeing, but wasn't bad enough to disable the car.

So far I'm optimistic. The car did not display the symptoms all the time, so I probably can't say it's definitely fixed yet, but I've driven it a lot and have not had the problem so far. I'll keep my fingers crossed! Thanks to everyone who offered advice.