This is not my car, but my friend's father car. They came to me for help as they knew I have a 1995 XJR6 and a 2005 X350 and have the VCM/SDD kit. I have no engineering background or training, just being regular visitor of the Jaguar Forums.

So this XFR suddenly stalled on the road and refused to restart. It was towed to a nearby parking lot for a quick diagnosis. The car hasn't been to the dealer for a long time so the SDD detected a page long of DTCs, starring the following:After reading the codes and while going through one of the advisories to "run certain programme", the car started fine. Using another scanner OBD Link SX only found three codes, two temporary ones "Fuel too Rich" and "Turbo/Supercharger Boost Sensor A Circuit Range/Performance", and a permanent code of "Turbo/Supercharger Boost Sensor A -circuit Range/Performance". As the car started fine during and after the scanning, she was taken home.

The next day, the car refused to start. Dash Board looked normal, lights, music, air-con, etc. all came on fine, just no start of the engine. Scanned it with SDD again and found the following codes:I noticed that the SDD highlighted the first two DTCs in red, and both notes to these two DTC mentioned "Message Missing from the Central Junction Box".

A bit of history prior to the the no-start. Eight weeks ago the car died on the road. ECU DTCs detected at the time included fuel pump failure and "Supercharger booster sensor A performance". The owner found a used fuel pump and after replacement of the faulty fuel pump the car returned to normal, but the engine light remained lit.

Obviously the "Fuel Pump Authorization" and "Lost Communication with Body Control Unit" are both related to the Central Junction Box. But what and where is the "Central Junction Box"? Moreover, I do not hear the starter turning when I pressed and hold the Engine Start button. Should I try finding a "Body Control Module" as a start?

 

The first thing I would do is check the age and condition of the battery.
If it's still the original battery it's well overdue for replacement.
On the XF a dodgy battery causes all sorts of problems and literally dozens of codes.

 

I suspected that one too, but battery is 2 years old and battery tester showed it has 12.33V, 55% charged and had an overall score of 82%, i.e. Good to Recharge. Also, using jump start does not help in any way. The starter does not turn, and pressing the start button simply shuts down the car entirely.

Additional info: Mileage is 70,000 Km; engine light is on; dash message centre shows "Service Required".

 

Some have had issues with the brake pedal switch when attempting to start.

Some have had to press very firmly on the brake pedal to get the engine to spin over.

 

Yep, that's your next check. Press the brake pedal with all your might when you hit the Start button.

 

Thanks, it worked! I have done more research about this strange phenomenon. This may have something to do with the Brake Pedal Switch which is probably on the way out. I scanned the car using another diagnostic tools and found an air leak somewhere in the brake system so sometimes you need to step on the brake real hard to start the car, and sometimes just normal pressure.

The real cause of the car dying on the road is yet to be found. All codes have been cleared today. I shall see what codes remain or if there are other new codes tomorrow.

 

Here is an update. XFR started fine, all codes cleared, but 54 codes returned, with one permanent Code P0236 Turbo/Supercharger Boost Sensor A - circuit Range/Performance.

Saw some previous discussions on P0236 before, so carefully tried to look for any leak in air hose/tube near the MAP sensor. A rubber tube near the supercharger actuator simply snapped when touched - it has turned extremely brittle, simply broken into pieces (see pictures).





The heat there has totally toasted the rubber tube. The mechanic advised to replace all tubes nearby. Wonder what parts are there, as the JEPC isn't very clear.




Other codes that remained
P0054 Bank 1 Heated O2 Sensor resistance fault
P0060 Bank 2 Heated O2 Sensors' resistance fault
P00C6 Fuel Rail Pressure too Low - Engine Cranking
P0481 Cooling Fan Relay Circuit Fault
P050F Brake Assist Vacuum too Low
P0573 Brake Switch Circuit Input High
P0504 Brake Switch A/B Correlation
P2135 Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation
P250C Engine Oil Level Sensor Circuit Low

The priority now is to prevent the car from stalling while on the road, and safeguard the braking system.

I am also very concerned with Code P00C6 Fuel Rail Pressure too Low; heard that rather than the fuel pressure sensor this may indicate a high pressure pump failure (not the one in the fuel tank but in the engine (but where is it?). The high pressure pump is very expensive. Additional background is some two months ago, this XFR fuel pump failed and was replaced. The workshop at the time found him a used pump so the owner could repossess the car. Not sure if this latest Code is related, or should there be other codes if the used fuel pump is the suspect.

I also do not know how to interpret Code P2135 Throttle/Pedal Position Sensor/Switch A/B Voltage Correction.

Haven't worked on XFR before, so would need some advice on the above, especially what new parts needed to be found.

 

Your still getting an awful lot of codes to have a good battery, I'd get it load tested, I've seen plenty battery's read good until you put a draw on them. And that P236 code is the result of the boost vacuum line break.

 

I have heard about the battery factor. No harm replacing it with a new one and start from there, just to rule out those fault codes emerging only due to a low battery, which tend to confuse and complicate the issues at hand.

 

My 2010 XF Premium had to have a new battery every year. It was very hard on batteries.