Dear Jaguar Enthusiasts,

I suddenly lost the engine and all electrical power while driving at night my XJR. There was no warning. I was able to recover while driving by putting the transmission into neutral and restarting the car, which to my surprise came back normal without any error messages. I then put the transmission back into drive and continued without any further issues.
There are no loose wires in the battery compartment.
I read the discussion in: https://www.jaguarforums.com/forum/x...t-lucas-48443/
What should I check for?
Thanks,
Stefan

 

Failing ignition switch ?

 

Thanks for you reply.
How to diagnose an intermittent failure of the ignition switch? Car ran fine today.
The voltage regulator had been diagnosed as failing for quite some time. Could this possibly cause the entire network to shutdown? Battery is in good condition.

 

What is the voltage across the battery terminals with the ignition in the OFF position when measured with a voltmeter?

 

The battery voltage is 12.14 V

 

No good. Possibly, the alternator does not provide good charge. Now start the engine and, at idle, measure the voltage across the battery terminals with the AC (blower fan on high) and headlights on.

 

Sounds like a loose wire from alternator.

 

It could be the inertia switch. When I first got my car, it would suddenly and randomly blink the headlights and cause the beltminder to ding as I was driving down the road. It didn't kill the engine, but after a ton of diagnostics, I learned that the inertia switch was going bad. It blinked the system for a split second, which caused the symptoms. I replaced the switch, and it fixed the problem. If your switch is bad, it could explain your issue.

The inertia switch is cheap and fairly easy to replace. Solve the voltage issue first as suggested above, but if you still have the problem, go here next.

 

I had a sort of extreme case that caused my electricals to ground out when braking heavy. Both my motor mounts were shot (didn't realize how bad til I dropped the subframe) and the metal transmission cooling line was bent inwards slightly. The combination of the two caused the trans cooler line to rub against the alternator positive cable and eventually wear thru the sheath and ground it out, only under that heavy braking load though. In my case though the shutdown was momentary and the engine usually wouldn't even shut off typically. Still worth a look there to see if that cable is loose or damaged in some way.

 

The voltage at the battery terminal while the engine is running is 13.85 V. My XKR has more than 14 V.

Stefan

 

The voltage at the battery terminal while the engine is running with high beam, AC at max and radio at max is 13.7 V.

I appreciate the suggestion that the inertia switch might be going bad - that makes a lot of sense.

Thanks,

Stefan

 

I'll also check for loose or worn cables. Both motor mounts, the transmission mount and the subframe bushings were recently replaced after I noticed significant vertical movement of the front end during braking. Perhaps this also damaged wires....
Thanks for the suggestion
Stefan

 

Sound like a frayed wire intermittently grounding out -- likely due to being frayed or broken while engine was shifting before the new mounts. Jiggle every wire you see . . .

And then go into the trunk (boot for you folks on the other side of the pond) and check the wiring from the battery.
Wife had this issue on her Maxima a few years back -- a 10mike mike wrench on the battery post cables fixed the problem.