Hi Need a little help

I was buying gas with ignition turned off and when I went to start the car the car would turn over and seemed like it was started for a couple of seconds then motor stopped running. The screen showed a red coloured battery and battery warning. I tried a couple times then waited for about 3-5 minutes then the car turned over. Is this definitely a low or dying battery or alternator issue?

 

Well given your general description I would say a dying Batt is a reasonable assumption. Check all the simple stuff first, but understand these cars are SUPER battery dependent and the Jag factory batt will just let go (AS DID MINE) with NO warning other than from the dash when its already dead. Usually if it's a charging issue you'll get a warning first but not always.

 

A battery will rarely let go like that, batteries fail mostly for one or two reasons, plate sulfation or plate shortage. You can't just guess what the problem is (well you can if you like wasting time and money). The most common symptom of a failing battery is loosing charge.

You might have a bad battery connection, a bad earth, a loose bonding cable between the block and the body for example, a regulator fault on the alternator and boiling the battery and so it goes on. An inexpensive multimeter will let you know at least the volts in the battery, it should be at least 12.5-13 volts....if it hasn't, disconnect the battery and charge it after checking the electrolight levels. If the battery is charged, refit it and try starting the car. If it starts connect the volt meter and see what the readings are...at idle it should read about 12.5-13 volts...as you raise the rpm it should max at about 13.5volts.....if you get a very high reading you have a regulator fault......what I am trying to say is that you cant just stick a pin in the map and hope, you need to diagnose in a logical sequence and some knowledge!

 

Have you or anyone else changed their own battery in car trunk of xf. I read about the BMS being connected to the negative terminal and that you need to take the car into Jag to get the battery changed, Has anyone changed their own battery and what happens to the BMS

 

You don't need to take it to Jag, I did mine but you will need to reset your windows and sunroof...Open them all the way close them holding the button until you hear a slight click, your done. BMS will figure everything out after a couple start and drive cycles.

 

You will also need to reset the E brake.

Just put your foot on the brake and set the E brake and release E brake 3 times.

If you don't the car will have a steadying beep at you as you drive.

 

Oh well....never mind!

 

thank you for all you help. I did not have a start up problem after the one incident. It seems the car turns over so I did take your advice to get a multimeter. Here are the results

Car sitting in garage overnight and the voltage was 11.88
When I started car the voltage was 14.58
When I turned on equipment with car running lights airconditioning radio etc the voltage dropped very little to 14.47

Being by myself I could not test for load eg start the car and see how much the voltage drops then obviously would pick up with alternator running

I think the 11.88 v (cold engine) shows signs that the battery need replacing and wanted your thoughts. I presume the 12.5 v is signs of good battery again thank you for your help

 

Modern cars will drain a battery if left for a while...but your alternator sounds good...if your battery is lead/acid, have you tried inspecting the electrolite levels? Most sealed acid batteries are in fact not sealed and can with a little effort be checked and topped up. If just one or two cells are down, the chances are it has a dead cell but you can still try topping it up (should cover the plates about 1/4". If after that and it is still giving grief, have the battery "drop tested", this places the battery under direct short load and will tell for sure. 11.88V could just mean that the vehicle has been left for a good few day or the air temp is cold, batteries hate cold!

 

Periodically the battery monitoring system module will instigate a self-calibration routine. To self calibrate, the battery
monitoring system first charges the battery to its full condition.
• NOTE: If the vehicle is only driven for short periods the charging process could take a number of days to complete.
Once the battery is fully charged, the battery monitoring system will discharge the battery to approximately 75% of its full
state of charge, but never lower than 12.2 V. The time taken to complete this part of the routine is dependent on the
electrical load on the vehicle.
When the second part of the routine has been successfully completed, the battery monitoring system will return the
battery to its optimum level of charge. The optimum level of charge will be between 12.6 V and 15 V, depending on
battery condition, temperature and loading.
The battery monitoring system module also monitors the battery condition with the engine switched off. If a low voltage
condition is detected the module can request the infotainment system is switched off to protect battery voltage. Once the
infotainment system has been switched off, the vehicle must be run for at least 5 minutes to charge the battery before the
infotainment system can be operated with the engine switched off.

I read somewhere that the system does this a couple time a year, can't remember where though....