Why auto start stop only lasts for 20 seconds?

[tomyin67]

The auto start stop function of my 2017 macan can only last for around 20s. before it forces itself to start again. I notice the battery voltage is around 12.3-12.4v before I first start the car every day. Could it be the low voltage of the battery that prevents the function from working properly?

[Paul]

Low battery, a/c on, slight steering angle....all will affect the stop / start function, and yes, all linked to battery capacity.

(...hateful invention; 1st thing I turn off every time I get in the car )

[pmg]

If you just been doing short runs with lockdown and afterwards , enjoy life and take it for a nice long drive!!

[Makanik]

...hateful invention; 1st thing I turn off every time I get in the car

With auto stop/start disabled, note that you also lose the coasting function, so there will be a double whammy on fuel consumption.

[Paul]

^^
Agreed (if there is any meaningful economy with stop/start,) but I had the diamond button programmed to enable glide when on a run.

[On-Track]

...hateful invention; 1st thing I turn off every time I get in the car

With auto stop/start disabled, note that you also lose the coasting function, so there will be a double whammy on fuel consumption.

One of the signs that battery voltage is down is coasting being disabled. I'm not too sure about the effect on fuel consumption. If your foot is off the throttle, is the engine still using fuel until it drops to idle? Even if the answer is no, fuel usage must be minimal.

[Paul]

I’m no expert () but I’ve often wondered....glide mode disconnects the drive so some fuel must go through to keep the engine on idle.
In drive, with no throttle applied, the engine keeps turning as it's still connected to the wheels but no throttle should stop fuel flow?
(Someone will probably know the answer)

[gmacan]

Personally, have long wondered what the ACTUAL gain in terms of fuel economy is with auto stop/start enabled, therefore inc. coasting, when comparing two absolutely identical journeys. Meaning one with it enabled, the other with it disabled. Assuming optimal condition of battery and weather exactly the same on both occasions. Obviously total saving is entirely dependent on number of stops and amount of coasting but, all things considered,
has anyone done any real-world comparisons and calculations?

It must be pretty negligible, I would imagine, in %age terms, but maybe worthwhile if doing a lot of journeys which involve 'the right' conditions.

[jaffacake]

Worth noting that for stop/start functions to exist, they already enlarged the battery and fitted additional re-gen functions. This allows them to comply with emissions testing and official CO2/economy figures. Testing is done from a full battery and stop/start optimised to kick in during those test conditions. Mnfrs don't care how efficient it is outside of official testing but it's likely that stop/start is worth using once you've gone to the effort of fitting all the extra kit needed. I'm not a big fan though and generally drive in Sport where it's intentionally disabled.

Taking your foot off the throttle usually cuts off fuel supply completely on an injection engine, as said above, the engine keeps turning due to drive from the wheels. The fuel cut off is what can cause nice pops & bangs from the exhaust when you open/close the throttle.

With coasting, you're right, the engine still needs to run...or does it? As soon as you come back on the throttle it can jump start itself from your momentum. Never come across this one before, so don't know the answer. Will find out.

We didn't buy these cars for economy though, did we?

[MikeM]

The auto start stop function of my 2017 macan can only last for around 20s. before it forces itself to start again. I notice the battery voltage is around 12.3-12.4v before I first start the car every day. Could it be the low voltage of the battery that prevents the function from working properly?

If it fires up as you stated without the a/c on or any other intervention by yourself (i.e touch/move controls) definitely battery, if you have a battery conditioner just leave it on for some time to bring it back to full charge state.