LairdScooby

Slave

Head

Seal

Sounds like it's lost a cell or two. That's the usual sort of figure i would expect from one dud cell. Disconnect (and insulate) the battery lead from the alternator and unplug the warning light/field wire so the alternator can't generate then try a fersh battery. It's possible if the alternator is dead and shorting the battery, it's what killed the battery or maybe even vice versa. Once you get past these problems, you'll be glad you persevered. 😉 😄

At the risk of preaching to the converted John, that depends whether the battery is ok or not, if it's gone it may hog all the available jump start current. Also depends on whether the "slave" vehicle has a big enough battery to fire up a Jag.

Method

Use some contact cleaner on those pins and also in the plug, remake/disconnect the plug several times then spray the contact cleaner in again and finally remake the connection. Doubtful whether that would prevent starting but i have no tech data on the XF so anything is possible i suppose. I would suggest it's probably capable of preventing things like the hazards and interior lights not working though.

Binary (197)

Flowchart

I'm not familiar with Japanese imports Graham so i had wondered if they had use an Aisin-Warner transmission instead of the ZF usually fitted. Experience with an AW in a Volvo 760 taught me the overdrive switch could sometimes play up bringing up a warning light indicating overdrive was off. From what you say, i'm guessing you have the more usual ZF box, some of the later 5-speed auto ZF boxes had their ECU mounted inside the gearbox, the seal could fail and this rendered the gearbox dead. This was more common on late 90s V8 models (X300 usually) but as you have a Sport mode, there is some electronic control. On the 4-speed if memory serves, the ECU is remote from the gearbox but i'm not sure where. If you can locate the gearbox ECU, follow the wiring from it and there should be an earth point somewhere nearby, i'd remove the connector and clean the connector and earth point - everything you've said so far points to a bad connection of some sort, probably an earth.

Sequential

Just a weird thought here Graham, do you have an overdrive button for your gearbox? If so, try cycling that off/on a couple of times before turning the ignition on.

Unique

Bespoke

The smell of burning semiconductors is different to that of an alternator or other wound component (eg motor, transformer etc) so that might give you the answer. If you stick your head in the footwell and have a good sniff, you should get your answer - if the BCM has fried, you'll smell it. The alternator windings will be a more accrid smell and most obvious under the bonnet, particularly in the region of the alternator. At this stage, guesswork won't do it, you need a proper diagnosis, hopefully your Jag specialist has autoelectrical training or at least, a working knowledge of electrical systems. Even then they can be tricky to diagnose.

Suit

Spot on John, fuses are an often overloooked source of problems. Going back to the days of "Continental" ceramic (and later, plastic) fuses, they were almost guaranteed to give trouble. Then blade fuses arrived and were much more reliable. However i've had many problems over the years with blade fuses, either the blades corrode causing a problem when they warm up and effectively disconnect the circuit or the fuse holder itself has overheated (usually as a side effect of the fuse corrosion) and melted the fuse holder. This extrapolates to all fuses to a greater or lesser degree so i totally agree with your analysis. The one point against it is that interior lights are a relatively low current draw so will drop less voltage over a resistive joint. As you allude to, it may still be the battery but could also be a poor connection, the lack of any electrical activity points to a general connector which is more likely an earth rather than a fuse if all circuits are down.

Wedding

You're correct if the car has the correct battery fitted which could in fact be part of the problem. If someone has previously changed the battery and not fitted an AGM battery, the stop-start will hammer the life out of a standard lead-acid and cause excess sulphation, drastically reducing the capacity of the battery. However, if the battery is fully charged and not even the interior or hazard lights will work, it's pointing towards an earthing problem somewhere, rather than fuses. That said, it could be a duff battery and an earthing problem..............

How soon after taking it off charge did you test that voltage? That could still be a dead battery.

I'd strongly advise getting the battery drop-tested by your local auto-electrician. That's showing about 60% charge at 12.4V, i would expect more to be honest if it hadn't turned over. This suggests the battery has lost its capacity to deliver current but the only way of doing it is to either get it drop-tested or measure the voltage while trying to start.

At what point did you measure the 12.4V on the battery? When you first took it off the car or what? Also have you measured the battery voltage while trying to start?

A few things come to mind, first is what fluid did they use in the gearbox? Second, what condition is the battery in? If the battery is not holding its charge that well, it can cause spurious faults on the gearbox ECU and other ECUs as well. The clue here is that it happens after a cold start, when there has been the most load on the battery to start it. By the time you've started it for the third time in the day, the battery would (or at least should) have enough charge to cope with a warm start without dropping the voltage enough to cause a spurious fault. As you might guess, my thoughts are directed at the battery being at fault here! Recently on my S Type, i hadn't used it for about 3 weeks and when i started, it came up with "Auto Gearbox Fault". I ignored it for a few miles, then hit the clear button and it went off and stayed off - hasn't returned since so i'm assuming that it was just a low battery. Sometimes it will also try and tell me a tail or brake lamp (sometimes both on both sides!) have failed as well if i haven't used it for a couple of weeks.

Legless

Skate