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Discussion Starter · #1 ·
Hi all coming back from London today my car dash lit up with the message in red " Stop safely, electrical fault detected. I pulled over and went through the "normal" switch off, lock and then get back in again. When I got back in the car displayed battery low, restart engine. ( I had done about 200 miles before I stopped). I started the engine which was very sluggish to turn over and started driving again. I got the car home but noticed that the battery was illuminated in the dash ( no charge I guess).
Has anyone else had this fault ? and if so do you know what the problem was ? Jag assist called out - they will be with me tomorrow morning as I am at home ( and the patrols are short on fuel), no problem with that as I'm home.
 

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From what you are saying I am guessing either an alternator fault or battery fault. The battery should be charged after a 200 mile trip or at least enough to start the engine easily. They will probably do a load test and see if the alternator is providing the correct current output to the battery, if so it is likely the battery is not holding the charge or may need a good charge to get back to optimum. I had a diesel Merc which was really sluggish starting due to me not waiting for the glow plugs to heat before turning over so put more strain on the battery which eventually dropped too low to start, I trickle charged the battery over night, waited for the glow plugs to heat each time before starting and never had another issue during a further two years of ownership.
 

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Discussion Starter · #3 ·
Hi, I think it might perhaps be the alternator, or as you say perhaps a dodgy battery ! I will update the post tomorrow once the tech has had a look. ( morning off work for me, yippee)
 

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If you have an electrical tester you could put it across he alternator terminals (if you can get at them) and see what it is putting out, I know on the XF it should be around 14.5v so would expect this to be in the same ballpark.
 

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Discussion Starter · #5 ·
So update on the problem.
Car is being recovered to Jaguar, the belt that driver the alternator has shredded. Apparently this is a known issue but they can figure out why the belts are failing ( apparently there is nothing wrong with the integrity of the belt so the suggestion is that the problem lies within the belt tensioner.
You will not know if you have a problem until the belt fails but the tech did tell me he was surprised that I managed to limp the car home as normally the batteries are depleted very quickly and then the car just stops.
Have a good day everyone, a hire car is on its way to me as I type.
Superb service again from Jaguar, it's just a pity the car has the problem.
 

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Is it a conventional alternator or a starter/alternator that is being increasingly fitted to some cars.
Shredding alternator belts?? Sounds like a quality control issue - again
 

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Glad to read you have found your issue, now what is the cause of the belt being shredded would be my concern as unless this part is replaced the issue will happen again and could leave you stranded.
 

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Discussion Starter · #8 ·
Hi all,
Just to confirm, yes it is a starter alternator on the car ( Bosch). I believe that there is some kind of issue with the tensioner in that it relaxes when the car is running and then "nips up tighter") when it needs to restart the engine. I believe that is probably where the problem lies. A relaxed belt suddenly being pulled tight ( just as load is put on it). That shouldn't cause the problem on its own though, many manufacturers use the same type of system and it works. It might perhaps be the actual angle of the belt or something like that.
In any event, the car is still at the dealership awaiting parts, hopefully it won't be to long 🤞
 

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The Bosch starter/generator uses a 6Vee belt drive and a very small drive pulley, ample for charging but high torque starting they need to increase belt tension to prevent slip. If it was high tension always the bearings would fail quickly, a similar system is used on the MHEV and PHEV at higher voltage.
 

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Of course, back in the day, you'd simply use a pair of tights tied round the pulley to get you home if your 'fan belt' failed.......which they did regularly!
 

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Discussion Starter · #11 ·
Well guys, got the car back. Belt has been replaced together with a new model tensioner which has hopefully sorted the issue. Everything appears fine but I have a nice long journey tomorrow - so we will see.
I've got to say though, it's a superb car and hopefully this is just one of those " new model gremlins "
 

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I had the same issue, fortunately able to stop on motorway slip road, but still a scary place to be and took 2 hours to be recovered. Police attended and were brilliant. Jag technician has just finished replacing belt and tensioners on our drive. Apparently a software update is supposed to have fixed the issue so perhaps we've been unlucky that the belt has snapped. The software change apparently means the belt isn't snapped into action during stop/start which is what put the strain on it, so it shouldn't happen again.
 
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