2007 Fabia no start electrical issues...

[pewdiepie]

Ok, 2007 1.4 16V fabia estate, unexplained flat battery upon trying to start, all dash lights on pre ignition as normal,  recharged battery overnight, still no start (no crank no sign of life at solenoid), fitted new starter and battery, no change, solenoid lead wire physically intact (but unable to get any voltage reading when key in starter position) have currently removed battery and positive cable to starter from the positive bus bar (this cable is not shorted to earth) but, all large cables fixed to positive bus bar on plastic battery cover even when separately removed and tested for continuity to earth all reading connected to earth....? Im guessing these are alternator pas hrw etc...? Looking for ideas here please!

 

 

[pewdiepie]

Sorted.  Ignition switch faulty. Switch £46. Auto electrician call out £45, upto £80 labour so far prior to fitting new switch (on back order from skoda) the dashboard is in pieces but hopefully will go back together nice and creaky. All caused by dead battery apparently causing excess current going through ignition switch..

[rum4mo]

Duff ignition switch okay, but maybe the reason for its failure is bit suspect, if all dead batteries handed over excess current then they might be in big demand?

[Breezy_Pete]

Thanks for letting us know the outcome.

Once it's all back up together, check that the battery light comes on with ignition, as there's a common failure involving the alternator excitation wire breaking, which can result in charging problems. If that wire is broken, the battery light doesn't illuminate at the 'ignition on' position.

[Breezy_Pete]

3 hours ago, rum4mo said:

maybe the reason for its failure is bit suspect

 

I was thinking about this over a pint at lunchtime, and it may not be completely daft.

Someone who actually knows about these things will hopefully correct me if I'm wrong, but the so-called stall current is the highest that an electric motor ever demands, zero rpm, therefore no back-EMF, maximum current. This is why electric cars are torquey as hell from a standstill, but much less impressive at higher motor rpms.

Usually, with a good battery, this only happens for the briefest of moments before the motor and crank start spinning.  If the time that it is at zero rpm is much longer (due to weaker battery), the surge will last much longer and try to burn out the weakest link, which may  have been the ignition switch in this case?

 

Any takers?

[Breezy_Pete]

Nah, doesn't make sense. If the current was higher, the thing would spin up.

Ah, but maybe the current is lower, but just lasting longer cos it's spinning up more slowly, if at all? Integrate the current over time and you get more energy dissipation in the switch contacts?

I dunno!

Edited 18 May, 2018 by Wino

[rum4mo]

Remember this was the ignition switch that was being discussed, so only slight changes in current as the battery got loaded and pulled down as this switch is only servicing low current supplies, the contacts in the solenoid would be handling the "power" current for the motor.

[Breezy_Pete]

Ah, excellent point!

[rum4mo]

@Wino I suspect that your choice of beer at lunch time has caused this error in logic!  

 

Talking about beer, I have just come back from a night away with my wife, my choice of places for once, Moulin Inn near Pitlochry - it has its own micro brewery just behind the Inn, 4 beers, all sampled as pints, job done!

[pewdiepie]

ok the day before the failure i stop started the car while in a queue of very slow moving traffic about 5/6 times (i wouldn't normally do this but it was a very hot day i had the a/c cranked up plus my coolant light came on (needed a top up) so i was worrying about overheating. I dont know if this caused or contributed to the battery death & subsequent ignition switch failure (because otherwise there would be a higher demand for ignition switches...). All i can say is it is a PITA but at least the car conveniently broke down on the drive at home. At first when appeared just a dead battery issue I bought a really crappy unbranded battery from kwik fit for a whopping £85 & it was only 40Ah, so glad i took it back for a refund (blagged them i hadnt fitted it) i've ordered a branded 62Ah battery online for £65 and that includes next day delivery...

 

[pewdiepie]

12 hours ago, Wino said:

Thanks for letting us know the outcome.

Once it's all back up together, check that the battery light comes on with ignition, as there's a common failure involving the alternator excitation wire breaking, which can result in charging problems. If that wire is broken, the battery light doesn't illuminate at the 'ignition on' position.

yes i will. thanks.

[Breezy_Pete]

7 hours ago, pewdiepie said:

coolant light came on (needed a top up) so i was worrying about overheating.

 

Find/fix the leak and check that both rad fans come on when A/C is operating.

Radiator thermoswitch is a common leak area, tighten up a tad for a free fix.