although it is right at the rear of the eng bay , it is accessible . there is a button on the side of the plug .
you basically just press the button and wriggle the plug upwards . and look in there .

 

Please define "good shape".

These cars, especially 2003+, are very finicky about battery condition. For the parking brake and DSC faults, please see this thread. It's a scorecard of what fixed them. The faults typically appear together:

https://www.jaguarforums.com/forum/s...attery-193787/


A little more history, too, please. Did the P0121, DSC, and park brake faults all appear together? Any recent work done? Has the car been driven regularly or has it sat for a while? What is your typical drive pattern, long or short trips? Your shoe size? Ginger or Maryanne?

 

#1 suspect by a mile - battery.

Needs to be about 12.6V after an overnight stand and without starting the car.

Check the rest once the battery is not #1 suspect.

 

 

That sitting is usually what causes battery problems. Was it on a ctek-type device?

 

Change the battery BEFORE you do anything else!
We have seen this countless times before. Especially if the car has been sitting.

Please erase all codes and make sure they come back.

Let us know what the fix was if you can?
.
.
.

 

As JagV8 asked, have you put the battery on a charger? Sorry to keep beating a dead horse, but what exactly did you do to test the battery? We've had many examples on the forum of batteries that show good with most load testers, but still let the voltage drop below a critical level during start. The general rule is you want to see at least 12.6V present BEFORE start. Below that, things get wonky. DSC and cruise control faults are the most common problems. 12.6V is quite high for a battery at rest, well above what most testers will call good.

If hesitant to throw a battery at it, and I don't blame you, try this: Put an automatic charger on the battery, at least overnight. Use something with at least 10A output, NOT a trickle charger. Keep the charger connected while you start the car and see if the faults clear. If so, low battery voltage was the culprit.

 

 

Sadly if you're sure, every other fix is liable to cost more and may be tough to figure out.

 

Was this a capacitance type tester? It's much higher tech than my trusty old resistive tester (aka toaster) but is also more finicky. I've had it tell me the same battery is.anywhere from 40 - 80% healthy, tested only minutes apart. Also, the "excellent" label was probably from the marketing department. The engineer who designed the tester probably wanted something like "No glaringly obvious faults at the moment". All I'm getting at is the results may not be 100% conclusive, so don't fall into that trap. My tester has an option to check with the battery installed or disconnected. If your tester has that option, the latter is much more accurate.

Have you fully.charged the battery and left the charger connected during engine start? If the car now.behaves, low prestart voltage was the problem. Won't cost a cent to try. If you don't have a charger, we will wait while you get one. For any electrical troubleshooting, rule #1 is always begin with a fully charged battery. I can't stress strongly enough how important that is.

Also, have you checked yet for water at the TPS connector, as previously suggested? Search the forum for P0121 and you will see many hits about water at the plug.

 

 

Thanks for the update.

The idea is to recalibrate (re-teach) the EPB's module's knowledge of the brake position.

 

There are a number of resets to do when a battery has been disconnected. Try those first (in sticky area)

 

 

It's the threads that stay at the top of the forum all the time. These are considered our "All Time Greatest Hits".
Look there to get a free copy of the shop manual too! (Called the JTIS)

But it's a great feeling to find such a complete and pretty cheap repair!
This forum has saved me thousands of dollars and it's a fun hobby too!
.
.
.