Non starting jaguar

[Bellasim]

Hi my jaguar keeps acting like it’s got a flat battery. I parked up the other day and when I came back it was flat then 5 mins later started no problem. Then yesterday it done the same thing but this time it never came back to life we have tried a booster pack on it and it will only try to start when u put it in boost mode u get a couple of turns then flat again. Thinking the battery is flat we have took it off and put it on charge but it had 12.4v in it when I put a multimeter on it so I’m confused. The battery terminals are tight I’ve checked both bcm’s the one in the boot and drivers side footwell for water damage but can’t see any I’ve not took the plugs out and looked at them yet that’s my next plan and the starter motor cable for corrosion. Any help would be much appreciated as I’m lost now. 

[LairdScooby]

At what point did you measure the 12.4V on the battery? When you first took it off the car or what?

Also have you measured the battery voltage while trying to start?

[Bellasim]

This was after we removed the battery and the car was acting dead. Never tested it when trying to start it. Thanks for the reply 

[LairdScooby]

I'd strongly advise getting the battery drop-tested by your local auto-electrician. That's showing about 60% charge at 12.4V, i would expect more to be honest if it hadn't turned over. This suggests the battery has lost its capacity to deliver current but the only way of doing it is to either get it drop-tested or measure the voltage while trying to start.

[O.T.H]

I agree with Dave and I think its a battery problem ????

How old is the battery ???

[Bellasim]

Hi again after the battery was on charge all day it was testing at 14.4v, my stop start was working before this all started so Im thinking the batterys are in good health. After fitting the battery to the car this afternoon after being on charge all day nothing happened couldn't get an interior light to come on or even the hazards absolutely nothing dead. 

[Bellasim]

I’ve no idea of the age of the battery I’ve only had the car just over a year 

[O.T.H]

You must check all connections ???

[Big John]

Hi

I would start by checking the Mega fuses. I think they are located on the side of the boot above the battery. Try following the Positive lead from the battery and you should find them.

John

[LairdScooby]

10 hours ago, Bellasim said:

Hi again after the battery was on charge all day it was testing at 14.4v

How soon after taking it off charge did you test that voltage?

10 hours ago, Bellasim said:

After fitting the battery to the car this afternoon after being on charge all day nothing happened couldn't get an interior light to come on or even the hazards absolutely nothing dead. 

That could still be a dead battery.

[N6 JMX]

I assume you are using a suitable charger for the battery? Your battery is NOT a standard lead acid, but an AGM (Absorbent Glass Mat) and should never be charged using a standard style charger. It must be charged by a charger with an AGM setting. The AGM battery has a very different charging cycle and has different internals.

The fact that you sometimes get interior lights and ignition, would indicate that the battery can deliver a small level of current but not cranking the car would be a sign that the battery is past it's prime. If the battery has a Jaguar sticker on it, it could well be the original and therefore at least 9 years old, which is well past the use by date for a battery in a modern vehicle - 5 years would be more typical these days with all of the onboard electronics.

You certainly need to have the battery drop tested to confirm it's condition, but even then, I would suspect it to be dead - especially if charged incorrectly.

N6 JMX

[LairdScooby]

1 hour ago, N6 JMX said:

Your battery is NOT a standard lead acid,

You're correct if the car has the correct battery fitted which could in fact be part of the problem. If someone has previously changed the battery and not fitted an AGM battery, the stop-start will hammer the life out of a standard lead-acid and cause excess sulphation, drastically reducing the capacity of the battery.

However, if the battery is fully charged and not even the interior or hazard lights will work, it's pointing towards an earthing problem somewhere, rather than fuses.

That said, it could be a duff battery and an earthing problem..............

[Big John]

"it's pointing towards an earthing problem somewhere, rather than fuses."

... I Agree it is unlikely that a Mega fuse has totally failed however they do themselves suffer from corrosion and can be a source of intermittent problems. If the Battery is indeed good, then the most likely issue is around an electrical connector most likely the battery terminals, battery earth (both visible) or the Mega Fuses (less obvious).

Regards

John

[LairdScooby]

1 hour ago, Big John said:

I Agree it is unlikely that a Mega fuse has totally failed however they do themselves suffer from corrosion and can be a source of intermittent problems.

Spot on John, fuses are an often overloooked source of problems. Going back to the days of "Continental" ceramic (and later, plastic) fuses, they were almost guaranteed to give trouble.

Then blade fuses arrived and were much more reliable. However i've had many problems over the years with blade fuses, either the blades corrode causing a problem when they warm up and effectively disconnect the circuit or the fuse holder itself has overheated (usually as a side effect of the fuse corrosion) and melted the fuse holder. This extrapolates to all fuses to a greater or lesser degree so i totally agree with your analysis. The one point against it is that interior lights are a relatively low current draw so will drop less voltage over a resistive joint.

As you allude to, it may still be the battery but could also be a poor connection, the lack of any electrical activity points to a general connector which is more likely an earth rather than a fuse if all circuits are down.

[Bellasim]

Hi everyone a thanks for the replies, after speaking to a jag specialist where it’s getting delivered too he thinks it’s more than likely the alternator has burned out as it’s now 6 years old and to be fair a week before all this started I had a right smell of burning one day on the way to work I thought it was coming from out side or it was the road water on the hot exhaust. Fingers crossed a new battery and alternator will fix her and it last another 3 years till the cars paid off 🥴

[Big John]

Hi Ross

I would still have a look around the mega fuses as a poor connection there could well fit your symptoms (including the burning smell) and I am not convinced a dead alternator would account for non-operational interior lights and hazards...

Good luck

John

[Bellasim]

That’s what I thought to be fair could the smell of came from the bcm in the drivers foot well 🤷‍♂️

[LairdScooby]

The smell of burning semiconductors is different to that of an alternator or other wound component (eg motor, transformer etc) so that might give you the answer. If you stick your head in the footwell and have a good sniff, you should get your answer - if the BCM has fried, you'll smell it.

The alternator windings will be a more accrid smell and most obvious under the bonnet, particularly in the region of the alternator.

At this stage, guesswork won't do it, you need a proper diagnosis, hopefully your Jag specialist has autoelectrical training or at least, a working knowledge of electrical systems. Even then they can be tricky to diagnose.

[Bellasim]

Spoke to a jaguar electronics expert at Edinburgh he also says it won’t be the alternator or the battery more likely a bad earth somewhere like you all suggest or the bcm in the boot. 

[Bellasim]

Finally got my car home checked all the big fuses first non blown removed the rear bcm and found corrosion on the bottom middle plug. Where do I go from here and would this stop the car from starting

[LairdScooby]

Use some contact cleaner on those pins and also in the plug, remake/disconnect the plug several times then spray the contact cleaner in again and finally remake the connection.

Doubtful whether that would prevent starting but i have no tech data on the XF so anything is possible i suppose. I would suggest it's probably capable of preventing things like the hazards and interior lights not working though.

[Big John]

Hi Ross

Can we just go back and explore in more detail exactly what happens when you try and start the car?

Are the key batteries OK? Does the car show any signs of "waking up" when unlocked? Have you tried starting with the key held over the sensor? Any lights on the dash? Have you tried jump starting from another car / starter pack? etc

Regards

John

[Big John]

Hi Ross

Are you certain that the booster pack you used was fully charged, and powerful enough to start the engine?

Re-reading your original post in isolation I would say dodgy battery. A decent starter pack will only require engaging "Boost" if it is unable to detect a voltage in the vehicle battery. To then only do a couple of turns with a fully charged starter pack suggest either the starter pack is not powerful enough (or is itself flat) OR their is a massive short when the starter is engaged.

Just because a battery reads over 12v at rest does not mean it is OK. My wifes Skoda failed to start last week. Started fine with my Noco GB50 attached but initial quick test by garage said battery was OK and at 80%. Only when tested again 2 days later did it show as knackered. New battery and now running fine.

Is it possible to try a jump start from another car with heavy duty jump cables?

[LairdScooby]

42 minutes ago, Big John said:

Is it possible to try a jump start from another car with heavy duty jump cables?

At the risk of preaching to the converted John, that depends whether the battery is ok or not, if it's gone it may hog all the available jump start current. Also depends on whether the "slave" vehicle has a big enough battery to fire up a Jag.

[N6 JMX]

I agree with the principal assertion here that the battery on the vehicle has to be suspect, followed by:

1. A corroded / suspect earth point(s).

2. A failed Starter Motor.

I would not try a jump start from a slave vehicle as that may transfer issues from one to the other. Start by fully charging the existing battery using the correct charger such as a Ring Automotive Smart Charger, the version with the LCD screen that indicates the battery status when charging. A battery that can take a charge should be able to be at 90% within 12 hours of connecting up and switching on. REMEMBER you are dealing with an AGM battery so it is vital the chosen charger has that capability. As given earlier, if a "standard" charger has already been used, then the innards of the AGM battery may already be shredded.

If you are not confident with battery tests, or indeed don't have access to the correct charger, then remove the battery from the car and hand it to a qualified Auto Electrician to both charge and test. You need to eliminate possible causes in an ordered manner.

N6 JMX