Fault but no Codes?

marlowboy

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Hi all, long time since I’ve Posted on here, been busy restoring a 30 year old GTO, joy!
2005 350SL has the Red Battery and Visit Workshop illuminated. I’ve put my Isoft Reader on her and it’s showing no Fault Codes......errrm, she has a Fault! Any ideas please? Many thanks again and stay safe!
 

Blobcat

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Charge the battery up and give it a good run
 
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marlowboy

marlowboy

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Will do, it doesn’t get used as much as she deserves, 16 years old and 61k miles!
 
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marlowboy

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Me again....... 250 Mile drive to the coast and back, also charged for 12 hours before we left, disconnected Rear Battery for a while, reconnected, it’s still on! Any other ideas before going to the Garage? Thank you if you can offer any idea.
 

peterws1957

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Me again....... 250 Mile drive to the coast and back, also charged for 12 hours before we left, disconnected Rear Battery for a while, reconnected, it’s still on! Any other ideas before going to the Garage? Thank you if you can offer any idea.
I would suggest checking the voltage of both batteries (how old are they?) standing and also with the engine running. If the latter is not 14.5 v ish, you may have a problem with the alternator or it's regulator. 12 hour charge and a 250 mile drive should have been more than ample to fully charge both batteries if everything else is in order.
 
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marlowboy

marlowboy

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Thank you for reply, I’ll have a look tomorrow.
 
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marlowboy

marlowboy

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Mercedes.....just checked output, Rear Battery which is 3 Months old shows 14.1V running
Front Battery is old! Showing 12.4V Running
im not the brightest but shouldn’t they be the same?

The old GTO, I’m still flatting and polishing after I gave it a very poor Respray! To embarrassed to show photos yet!
 

mioba

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12.4 at the front running. There is your issue. Your alty not delivering juice to the front. should be reading near on 14v.

And what did your dealer say. surely you didnt go there and ask them to measure V
 
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marlowboy

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Hi, no Dealer involved for this!
I can’t get my head round why the difference between Front and Rear, same Alternator. Is the Front Battery U/S?
 

sonic

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Hi, no Dealer involved for this!
I can’t get my head round why the difference between Front and Rear, same Alternator. Is the Front Battery U/S?
Same alternator different batteries. 12.4volts running the battery needs changing.
 
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marlowboy

marlowboy

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Same alternator different batteries. 12.4volts running the battery needs changing.
Hi again, i have now charged both Batteries. Front one is showing 12.86v and 12.50 when running.
Rear one is showing 12.42v and 14.03 when running.

I still can not understand why from the same Alternator I’m getting 2 different readings.......help!
 
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marlowboy

marlowboy

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Hi, no, should I have done and for what reason?
 

LostKiwi

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First thing in morning before starting and with no load applied check front battery voltage. Anything under 12.6v the battery is tired. Anything under 12.5 and it's knackered.

That's with the battery having been rested (not on charge, no load overnight).

That applies to all batteries.
 
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marlowboy

marlowboy

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Thank, I’ll check in the morning.
 


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