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Battery under seat

Started by braziersrus, December 16, 2021, 02:03:57 PM

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Hello, Thanks for letting me join. We have just acquired a non-running sharan 2008 4 motion. We have replaced the battery in the engine bay, but have found a second battery under the drivers seat. I have searched the internet but was unable to find anything relating to a second battery.
Any ideas as to the function of this battery?

I think you will find its intended as a leisure battery, its also sometimes there for the Aux heater - I would guess its more likely to be fitted where you have the 7 day timer unit for the heater so it can run the heater without the engine running to heat/defrost the car before you get into it. Most don't have one. wouldn't have thought that it would stop the car starting.

A few things will frequently stop them starting - more info would help there, petrol or diesel for example? Does it try to crank and fail to start, or refuse to turn over? Any fault codes? What does the led on the drivers door do when your trying to start?

Thank you for your reply, although I have been told off by my husband for not giving the full information. Men!!
The car was stood for 2 years at an airport, it worked perfectly well before it was parked up,
But due to covid the owners couldn't get to the airport here in France.
When they finally arrived and  tried to start it it it ran for a couple of minutes then cut out. We have recovered the car.
Put a new battery on it, drained all the old diesel out and put new diesel in.
Again it runs for about a minute or two and then just stops.
Any idea?
1.9 TDI.

Sounds like a lack of fuel getting through to me - You mention you drained the old diesel, have you changed the fuel filter as part of that?

I think there can be issues with the fuel pickup in the tank particually if the tank is low on fuel, but someone else would be able to better advise on that (think its something to do with it allowing air to leak in and casuing it to stall).

Will it restart once it cuts out? Or does it crank but fail to startup? Could be a relay 109 issue (search on here for more info) but think fuel is more likely given the times you mention (and filter a good possibility if its been on there some time before it was parked up)

Dread to think how much that airport parking bill was!

Yes, I think Brian's advice is wise as usual, try changing the fuel filter. May well be gummed up after all that time. Also have u considered putting a bottle of redex in the tank, that stuff fixes anything lol

Also could just be old fuel in the fuel lines, maybe crank some of it out and just keep trying to start the engine, if u can get it going for a few minutes it might just be enough to clear the cobwebs out so to speak
I drive a Seat Alhambra 1.9Tdi which has 115bhp and an automatic gearbox.

I am happy to help you with all your questions. I am not a qualified mechanic but seem to be better at fixing my car than even the most experienced garages.

I have lots of friends here and very much enjoy talking with you all. Always remember, a motor car is a serious tool and should be treated with respect. Put your safety first, always.

Another thing I forgot to mention oil and fuel filters were changed.
Fortunately the car parking was on a years ticket which was renewed.
Will pass on the information about the relay.

It does start each time but cuts out, he does think there could be a problem with fuel getting through.

The leisure battery is flat, how important is this?

Not sure the second battery will matter for the starting/running issue, as most don't even have the second battery anyway. You could try charging it to see if it will take a charge, but think its doubtful its of any relevence to your issue personally.

Its possible you have an air leak into the fuel system - easiest way to tell that is to replace a section of the pipework with some clear pipe as a temp measure so you can see whats going on, that should allow you to rule out or narrow down a fuel issue. Given the filter etc has been disturbed its possible theres something wrong there which may be causing the issue. How was the tank emptied? Via the access hole or by pumping out the contents?

I don't think the second battery was ever fitted to UK cars so assume this must be a European car or has been fitted after market.
It's job as Brian mentioned is to power the auxiliary heater when the engines not running ensuring there's always enough power in the main battery to start the engine.
What you can try is to remove the inlet pipe to the fuel filter from the tank place the pipe in a jam jar then just turn the ignition on, observe, you should get fuel pumped into the jar for a few seconds, if not.
You may need to remove the intank fuel pump to clean the filter screen, there is a plate in the floor under the second row of seats and carpet to do this.
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To chime in here (a pleasant break from fixing the forum lol) Chris is correct that the battery was never a UK option. You could buy what they called a 'dealer kit' to have it installed later though so that's possible, but I'm fairly sure the 4motion was discontinued circa 2006 by VW in the UK so again, that would make me think it's an import - although its not really that relevant to the issue tbh. The secondary battery was indeed fitted to operate the parking heater, if its factory fitted then your roof clock will have 4 buttons around it including a SET and 'Flame' icon. Either way though it shouldn't have any impact on the car, and if you can start it then its moot anyway as a flat battery won't cause a running motor to die unless the alternator is also defective.

You say it runs for about 2 minutes - can you clarify
a) how does it die? Just cuts out or splutters, falters and then stops.
b) What happens if you elevate the revs after start? Ie, sit with your foot on the throttle to say 1600RPM - does it still die?

I'm thinking the same as the others in that its fuel starvation, how much fuel was in the tank whilst it was sat? Diesel, especially cheap diesel which has a higher moisture content, is amazingly good at growing algae (yes weird but true) known as Diesel Bug - with two years that could likely be quite significant so the filter and injectors are probably gummed up. I'd be swapping the filter, and filling the new one up with 50% diesel 50% injector cleaner before fitting, then start it and hold the revs at 3Kish to put the cleaner through at pressure.

This is a boat filter (Image from BSAC)


Its especially prevalent in leisure boats which sit for long times but it forms a horrible gunk that may need special treatment if its too far gone, what was the old diesel like that you drained out?
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Yes, my thoughts exactly. Try and get it started a bit, try and get it revving up, get fuel and cleaner flowing, rev it up if it keeps running. Sounds basically like a nice Italian tuneup is what's needed here. A dam good thrashing should blow out the muck.
I drive a Seat Alhambra 1.9Tdi which has 115bhp and an automatic gearbox.

I am happy to help you with all your questions. I am not a qualified mechanic but seem to be better at fixing my car than even the most experienced garages.

I have lots of friends here and very much enjoy talking with you all. Always remember, a motor car is a serious tool and should be treated with respect. Put your safety first, always.

Thanks for all the replies with regards to our fuel problem. Sorry, I can't locate my original message, but the sharan is in need of a new relay 109 and fuel pump, as correctly mentioned by you brilliant people.
Parts have been ordered, so fingers crossed.

##Merged Topic## - Mirez 21/12/2021

I wonder whether braziersrus might be persuaded to tell us about her adventures with the Sharan? Did the relay and the pump solve the problem and is the vehicle running OK now?