Failsafe Mode ?

[alanXK8]

I've just been getting this message occasionally when starting up my 2001 XK8 Conv. hot or cold. It seems to go away if I turn off and re-start the car, after which it runs perfectly.
The main agent did a computer check and came up with a variety of "records", none of which he thought was much of a clue. He cleared the history but the fault re-occured the next day.
A further computer check then showed the fault code P1632, which was also one of those which came up the first time, so seems to indicate a possible cause. However the technician didn't know what the code meant.
I'm told that even quite minor circuit problems almost anywhere on the car can trigger the failsafe mode to operate. Can this be true?

Has anybody got any bright ideas?

[mike020150]

P1632 code refers to the generator circuit. Since the fault code appears at start up when battery voltage will take a dive, there's a fair chance that it may be due to your car's battery being past the first flush of youth. Many spurious XK fault messages are produced by low voltage. So, it's always a good place to begin the search for almost any of them! Mike.

[alanXK8]

Wow, what a quick and useful response. Thanks Mike.

I had suspected that a low battery might do this but rather rejected it as I always keep my battery on trickle charge. However, would I be right in thinking that if the battery is getting old then once I am out on the road the battery voltage might drop in use, and hence cause this "fault" to appear? Funny that it goes away after a second restart though?

If it should not be the battery itself would the next search be on the generator itself, or the wiring loom that leads there?

I've been told that a wiring break anywhere on the loom might cause this kind ofmessage to appear, which is rather frightening, (needles and haystacks spring to mind). But presumably the P1632 code will provide the all important clue?

[mike020150]

The XK8 electrics are so sensitive to battery condition that I'd start either by getting an auto electrician to carry out a drop test on your battery or by borrowing a known-to-be good and nearly new battery, perhaps from a local JEC member, to see if the same fault message appears. Alternatively, take a gamble and buy a new battery ensuring that its capacity at least matches (preferably exceeds) the OE Jaguar one. If that doesn't solve the problem you really need someone familiar with Jaguar electrics. They don't take too kindly to just anyone poking around witha multi meter! I'm afraid the fault code can only indicate the approximate area of concern and even then the code may be spurious. This is why it's always important to eliminate the battery voltage issue first. Good luck. Mike.