"Hill Start Assist not available" warning (occasionally)

[alanfp]

Apologies for long post but I might as well give you all the info that I have now....

Over the last couple of months the "HSA not available" warning has been coming on occasionally, usually once I have come to a halt at a junction, not necessarily on a hill. It's getting more frequent.

I've owned the car for 7 years and it's only just started doing it. I suspect low battery voltage, although when I needed a new battery 3 years ago I never had the HSA warning appear. 

Batt readings with a multimeter:-

when engine just turned off 12.08V

when engine off for 20 minutes 12.30V

Voltage across battery terminals when being charged by alternator 14.1 V (fluctuates 14.0 - 14.2) with all elect loads off, 14.0 V (fluctuates 13.9 - 14.1) with fan and headlights on.  I have never had to resort to charging the battery with a charger.

I would have thought these readings were OK but are they a sign of an imminent electrical problem?

Or is it just a sign of old age and I'll just live with it ??? (much like my own ailments!). 

Any advice appreciated.

 

[unofix]

There is at least a 90% chance it's a simple case that the batteries health is failing. The voltage of 12.08V is very poor and even once the car has started to enter sleep mode a voltage of 12.30V is still only 70%

Your car uses a Smart charge system and as such charging voltages between 13.6V and 14.9V are quite normal and will constantly change.

Time to open the wallet and dig deep, looks like you need a new battery.

[alanfp]

Thanks for the reply. I expect you're probably right about needing a new battery, although it is less than 2 and a half years old.

But why is my car giving me a warning (which stems from a low batt voltage, I understand) while the engine is running, because the voltage across the batt terminals is 14v.  How does it know that the sleep voltage is 12.3v? Or does it remember that and then say "when the car has been driven for 10 minutes, I'll tell the driver that there's a battery problem". Or is it just magic???

[unofix]

The 'battery Monitor System' (BMS) monitors all current been drawn from the battery and all charge current flowing in to the battery. It knows the state of charge of the battery when it was parked and can easily calculate how much of the capacity has been used and what the present SOC is.

This is why on vehicles equipped with BMS that when charging the car battery you must charge it while the battery is still connected to the car. Also the battery charger positive lead has to be connected to the battery post, but the negative charging lead needs to be connected to the chassis earth point (NOT the battery). This then allows the BMS which is fitted to the negative battery post to monitor the charge and update the known value of the SOC.

[alanfp]

5 minutes ago, unofix said:

It knows the state of charge of the battery when it was parked and can easily calculate how much of the capacity has been used and what the present SOC is.

That makes sense, thank you.

[PaterAnt]

Try resetting the battery monitoring system: 

1. Get in to the car and do all from points 2 to 4 within 10 seconds.
2. Turn on ignition with engine off (key in position II) . Turn on headlights.
3. Turn on and off 5 times rear fog light switch .
4. Turn on and off 3 times hazard light switch .
5. If everything goes OK battery light will flash 3 times on cluster within next 15 seconds.
6. Resetting BMS is now finished, so turn off ignition.
NOTE: To make fog lights work, you need to do this with headlights "on".