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.

 

Here is one from fellow long standing member Jon89. Had a lot of us stumped back in 2015. Well worth the read, somewhere page 2 or 3 are the actual codes Jon posted on this subject:

https://www.jaguarforums.com/forum/s...ilable-141375/

 

Thanks, that was a VERY interesting thread. Per post #80, the root cause was the EPB module. So for the scorecard, that one was obviously not the battery.

Curiously, see post #10 in that same thread. A new battery was fitted by MyBlackCat, but initially that was no help. Turns out that when sold a battery typically is not fully charged, so a few hours on a charger took care of that. I'll score that as a new battery being the fix.

 

LOL, how about your own experience here?:

https://www.jaguarforums.com/forum/s...k-32699/page3/

Your fix (new battery) was in post #9. See posts #23 and #34 for two more examples.

 

Can't really say whether it's fixed the problem on my 2001/2 4.0L V8, but I've had no re-occurance of the "engine failsafe mode" warning since I've used the battery tender.
I haven't replaced the battery as yet, but it is on the cards, just got to get to the suppliers.
Admittedly my journeys are short in comparison to others maybe, only 7 miles each way with a 12/13 hour stand in between.
Here's the link to mine
https://www.jaguarforums.com/forum/s...orning-192931/

 

That's short enough to flatten many a battery on many a car.

 

Another check mark for the battery:


https://www.jaguarforums.com/forum/s...8/#post1727908

 

This thread had a battery that didn't fix it, post #33:

https://www.jaguarforums.com/forum/s...7&postcount=33


From the same thread, post #35, another strike against the battery. Also note how the module replacement wasn't plug and play, but had to be programmed:

https://www.jaguarforums.com/forum/s...8&postcount=35

It seems to be common for multiple faults messages to appear at the same time, typically not just "Park Brake Fault", but also "Cruise Not Available". I've wondered if a failed parking brake module would only cause the one message, and multiple messages always indicated a battery-related problem affecting more than one system. Such a change in symptoms would be a big clue for troubleshooting. Alas, it's not so, per the last link above, as a failed parking brake module caused both messages, just like with a bad battery.

 

I guess as the cars age and have already had new batteries more things will turn out to be wiring, connectors, motors, modules, ...

As the EPB parts commonly get no servicing, I imagine the motor draws ever more current and either it or the module will suffer.

It's still commonly the battery as #1 suspect, though!

 

This one was the EPB module:


https://www.jaguarforums.com/forum/s...2/#post1830989


Also note the important details about the exact match of the entire part number with any replacement.

 

I'll score this one as batteryish:


https://www.jaguarforums.com/forum/s...-drain-196302/


The root cause was the alternator not properly charging the battery, as opposed to a bad battery itself.

 

 

heres one for (water in the TPS plug)

thought id throw this in here .
as mine had this code accompanying the DSC fault ,cruse control fault and park brake fault .
seems uncanny to have the same symptoms though a different cause .

Just to point out that my 03 STR when purchased , had an accelerator pedal position sensor code p0121 and a message center full of faults . also limp mode or restricted performance if i remember .
and this turned out to be

(water in the TPS plug)

as so many Early STR's had problems with , causing limp mode and multiple message center faults displayed and the dash and a p0121 code ,
there is a TSB for the repair too ,

as these plugs have vents and are not sealed and water drains on to the TB from the wind-sheald scuttle panel .
I never replaced any thing relating to the problem , just cleaned out the TPS plug,
and wire brushed the corrosion , and then sprayed wd-40 in there , and silicon sealed the plugs, vents and wires, no more problems with this since 2014 ,
also the same battery remained in the car for three more years after this , it was not the battery at fault !
it was not the EPP at fault ,
so just a heads up for any one else with these symptoms .

the dealer had replaced the whole throttle body one year before me purchasing the car for the same fault .
under warranty .
for it only to return as the cause was not fixed . and the warranty ran out ,
hence the car being up for sale , the previous owner had enough of it .
lucky for me .

 

Here's one more, but this belongs in the "NOT the Battery" column:


https://www.jaguarforums.com/forum/s...module-204986/

 

One more for the scorecard, note the slightly different symptoms than usual. In both cases reported here, a worn-out key cylinder was the fault:

https://www.jaguarforums.com/forum/s...-maybe-211809/

 

One more for the "Not the Battery" camp, please see post # 4 in this thread:

https://www.jaguarforums.com/forum/s...8/#post2047033

In this case, a new battery didn't help. The fix was to clean and reseat the connectors on the RECM and the EPB controller.

 

Wonder if the boot (trunk) had been wet at some time...

 

Here's one for anybody cheering for the battery:

https://www.jaguarforums.com/forum/s...helped-221589/

 

The control module was the culprit here, post #9:

https://www.jaguarforums.com/forum/s...1/#post2130373

 

So I know what the failure mechanism is and how/why the faults occur.

First a little background info. I am an experienced shade tree mechanic. I have fixed, tuned, built, rebuilt and improved many a car and truck from since I was 14 years old. i am 56 now. I do ALL my own work except for tire mounting/balancing and alignments because I dont have the tools.

For my job, I work as a reliability/mission assurance engineer for an aerospace company and a huge part of my job is troubleshooting complex electrical components that go on military and space vehicles and satellites. I troubleshoot to determine the failure mode, and determine the root cause and implement corrective action to prevent reoccurance. I also assess reach-back. Many items I work on are computer controlled.

So my assessment of these failures on our jags pertain to other cars as well (reachback).and can all be related to the same thing and its something Ive seen on my own new to me '06 STR which lived its life in sunny southern california.

Drum roll please.................

Corrosion on various connectors.

Yes as simple as that. I had an issue with my DCCV not working right. It was connector corrosion that caused it not to work. My intercooler pump didnt pump. I cleaned the connector and it started working again. I then replaced the pump with the high output mercedes pump for better performance.

And now my HID headlight too. Drivers side bulb didint work and I found massive corrosion on the connector. My car is missing the belly pan and top radiator cover so water can easily get up inside places where it normally couldnt.

So why and how? Well with computer controlled electronics, they rely on sensors and feedback mechanisms to ensure the proper signal levels are being provided. When the levels drift outside normal ranges, things dont trigger the computer to do the things they are supposed to do. THIS IS WHY A LOW BATTERY CAUSES PROBLEMS. Because the signals used by the computor which might need to be 1.24v to 1.8v are now at 1.1v because the battery is lower than normal.

Corrosion will do the SAME THING. Corrosion is an oxide layer that form when the oxygen in the air or water causes an oxide layer to form (its chemistry). oxide layers are higher resistances than plated connector pins and sockets. When water causes corrosion on the pins, the resistance goes up, voltages and currents go down and the computer gets bad data and then flags a fault.

CHECK YOUR CONNECTORS!