207 Battery warning light, it's working but NOT working ? ?

[uncle buck]

Hi all,

2009 - 207 1.6 HDi

The battery warning light comes on with the ignition and goes out when you start the engine as it should.
The battery is in good condition & charging as it should, 12.6 volts before start, 14.5 volts when running so all good so far.

However, I noticed that if the engine is run with auxiliary belt removed so the alternator is not turning there is no battery warning light illuminated or any warning message

All connections to the alternator have been removed and checked and they are all in good clean condition.

Anyone out there with any idea on this issue ?


Cheers.

[PaulC5]

Why are you having to run the engine with the aux belt removed ?

[mickthemaverick]

An interesting one, I would suggest that the battery warning light is designed to come on at a specific voltage at the battery. I would guess that voltage to be around the 11.9-12V point so if your battery is showing 12.6 V with no alternator it may not be low enough to trigger the warning lamp. If you turn on the heated rear screen and the headlights with no aux belt and still get no light test the Battery volts at that point. If it is still above the threshold you have to leave it running with everything on and no charging until you read high 11s at the battery, at that point I'd expect the light to come on.

[xantia_v6]

I think that it is a "controlled" (Lin bus) alternator, so the warning light is not connected to the alternator, but is controlled by the engine ECU. I am a bit surprised that there is no error when running the engine with the belt removed, our 308 throws engine fault like 'alternator speed implausible ' under similar conditions.

[uncle buck]

Thanks for the interest

Why are you having to run the engine with the aux belt removed ?

Changing the timing belt, started engine to check all ok before aux belt was replaced noticed charge light was not lit.

@ mickthemaverick
I'll try your suggestions and see if the warning light comes on.

@ xantia_v6
Yes you would expect it to throw a wobbler wouldn't you, strange.

This car has electric power steering so the aux belt only turns the alternator & the Air Con pump, so if you didn't have the AC on & the belt snapped you would have no idea anything was wrong in the absence of a warning light !

Cheers

[uncle buck]

An interesting one, I would suggest that the battery warning light is designed to come on at a specific voltage at the battery. I would guess that voltage to be around the 11.9-12V point so if your battery is showing 12.6 V with no alternator it may not be low enough to trigger the warning lamp. If you turn on the heated rear screen and the headlights with no aux belt and still get no light test the Battery volts at that point. If it is still above the threshold you have to leave it running with everything on and no charging until you read high 11s at the battery, at that point I'd expect the light to come on.

Mystery solved . . . It works just like you said.

I hooked a multimeter to the battery & started the car the voltage was 12.50 V after starting, I put all the electrics on, headlights, fog lights, heated rear screen & blower which dropped the voltage to around 11.90 V still no warning light so I let it sit ticking over like this for a while. The voltage was dropping quite slowly but after 5 minutes or so the voltage was flickering around 11.50 v then it happened.....the battery waring light came on with a beep sound & a message on the central display saying "Battery charge or electrical supply faulty"

I've only tested it with the car stationary maybe if the car was being driven the warning light would come on earlier.

Thanks to all who replied


Cheers

[PaulC5]

We have all learnt something again, thanks for posting. Probably not a test to repeat often since it could ruin the battery.

[mickthemaverick]

If you were driving the car in that test state then the warning light would come on quicker simply because you would be adding extra load to the battery with the ignition circuit doing its stuff and things like brake lights using power so you would drop the voltage to the trigger point, apparently 11.5V, sooner and hence get the light sooner. You shouldn't do any permanent damage to the battery as it is designed to supply a much higher current when you are using the starter motor than it will be supplying under these test conditions. However it does mean you put the battery through a complete discharge - recharge cycle which does reduce the life of the battery by 1 cycle of course. Glad it has resolved your 'mystery'

[uncle buck]

In the good old days of simpler vehicles if your fan belt broke the battery warning light came straight on, throw into the mix a load of electronic wizardry and we're no further forward and more confused

Well I now know the warning light works.... that's my inquisitive mind satisfied for now.

Thanks.

Cheers.