Originally Posted by kr98664

Cordial Greetings All,

After some time on this forum, I've become fascinated by how often 2003+ cars will experience certain faults due to a worn-out battery. The primary purpose of this thread is to act as a scorecard to see what has and has not fixed the problems.

Specifically, forum experience points to warnings for the hand brake, cruise control, and DSC systems if the standing battery voltage is below 12.6 before start. For reasons unknowns, the controlling computers are very cranky and will generate fault warnings if the battery voltage is below the magic 12.6 threshold.

Please keep in mind this low voltage can be caused by several factors, either individually or together. A low battery may still start the engine just fine, so don't use starter cranking speed by itself to say your battery condition is good:

1) Old or defective battery with one foot in the grave, unable to hold a charge overnight.

2) Low charging voltage from the alternator, so the battery never gets a full charge in the first place.

3) Driving routine of mostly short trips with high electrical loads (HVAC, lights, etc.), so once again the battery never gets a full charge in the first place.

4) Some type of drain, causing an overnight run down of a perfectly good battery.

Although I've listed several possible causes, the first one (the condition of the battery itself) seems to be the most common root cause.


Here's a great starting point for your reading pleasure, with a detailed explanation of how low battery voltage before start will cause you grief. Lots of good info about adding a battery tender, too, for cars that are not driven daily:


https://www.jaguarforums.com/forum/s...pe-faq-123983/


Specifically, please see post #8 in the thread linked above, where a known-bad battery was deliberately installed, and caused the bevy of faults. Once a known-good battery was reinstalled, the faults cleared. That is one great example.

Here are a few more examples. In these cases, I've used the permalink to a specific post within a thread, to make it easier to find the resolution without having to dig through a long thread:


https://www.jaguarforums.com/forum/s...6/#post1806843


https://www.jaguarforums.com/forum/s...2/#post1808357



For some balance, here are a couple of examples where the battery did not fix the fault, but there's still plenty of interesting reading there:


https://www.jaguarforums.com/forum/s...oltage-179828/


https://www.jaguarforums.com/forum/s...ilable-192080/



On a side note, while researching for this scorecard topic, I found a LOT of threads with no resolution. As a favor to all, if you originate a thread, please come back with an update, even if we were all wet with our suggestions, or the problem still continues, or even if you gave up and sold the car...

On another related note, I'd like to keep this thread as a simple scorecard to learn what fixed the typical DSC/hand brake/cruise control faults on 2003+ cars. In my little imaginary world, I envision this thread as mostly a series of links to other threads, with just a brief explanation of each.

If you need specific troubleshooting assistance with these faults, please start a new thread, and of course update it with the fix, and then add a link here with a brief description. That way, the next time somebody poses a similar query, we can direct them here and let them read through the many results to assist in the decision whether to replace the battery, get a battery tender, etc.