I had the same problems a few months ago.
It was the battery. Mine was 7 year old, so I bougt a new one.
But at first that changed nothing.
In my garage they fixed the problem by charging the battery for a few hours, because the new one was not fully charged. It came from the shelf in the store direct into the car. In the garage they explained to me, you have to charge a battery from the shelf before you put it into the car.
So try and meassure the power of your battery and, if needed, recharge it for a few hours with a charging device. Just driving arround to recharge it might not be enough.

 

this maybe going off topic a little but i was working on an stype 04 last week with similar issues,

turned out to be 2x 8mm bolts had worked loose that holds the transmisson selector cable!!

will worth jacking the car up to have a quick look; if the 'j' gate & rotary switch give out conflicting signals it can bring up this code/fault. hope this helps.

 

It has a new battery fully charged.

 

Rob, thanks for the addition. I knew the x350 XJ were notorious for the bolts magically loosening...thats the first time I've heard of an s-type being afflicted.

 

I had the same "transmission fault" happen to me today. When I was driving this morning the shift change from 1st to 2nd was not as smooth as usual. On the way back home from the store the transmission fault happened and it effected performance. I limped it home, afraid that if I shut it off where I was that it wouldn't come back on. Parked in the garage then restarted after a few minutes and the error was gone . I know for a fact that I need a new battery (because it shows needing a recharged when they checked it out at my auto shop a few weeks ago) but do you think that would be causing the problem with the shift change and the transmission fault?

 

Duff batteries cause all manner of error codes in our cars, very likely.

 

Car did it again two days ago. Had been sitting for a week or so. Same P1642 code. Trans stuck in park and half a dozen other warnings. After restarting about 10 times and clearing the code, it finally cleared up. Only happens on initial startup.

 

With all the various and sundry error codes and faults that seem to plague the owners of these older Jags coupled with the seeming lack of any real 'fixable' causes for these anomalies I think we're dealing with the constant plague of all electrical system both ancient and bleeding edge, the much maligned GREMLIN.

What with loosening bolts, weakening batteries, inconsistent grounds from the build up of corrosion and its accompanying increased electrical resistance, to aging intermediate sensors and connectors, it's a wonder some of these cars are even drivable. As most of you know modern Formula 1 cars need a computer in order to even start due to their increasingly complex electronics packages so can the day be too far away before we lowly highway plodders will be saddled with much the same requirements?

Unless you have a hard fault that is obviously not going away with a restart or code clearing session I would suggest a periodic check and cleaning of all grounds and reachable sensors and connectors with special attention to all those with exposure to the elements.

Just my two cents worth but years of building and debugging computers has taught me to first check for the simplest and most easily remedied causes.

 

Where is the ground (earth) point in the front?

 

Behind the headlights-remove plastic cover across the front to access.

 

There are too many to successfully point them out in a message so go to the file download area and grab the X350electrical.pdf.

The link...I think: http://www.mediafire.com/?sgk9xz531xra74i

Page 17 shows a schematic of all the grounds and probably can help you troubleshoot your systems other potential weak spots.

An additional thought. The transmission and parking brake have an electronic interlock system so that when you put it in park and remove the key it automatically goes into parking brake applied. It's supposed to release automatically when you start the car with your foot on the brake pedal. If it DOES NOT disengage the transmission may remain locked in park unless or until you MANUALLY release the parking brake by pushing down on the console mounted switch. Could that be your occasional problem??

 

Manually releasing the parking brake does not help. Think I will park with it off from now on.

 

Got a new battery a few days after this post and the error codes & shift change cleared up.