Stop start not working... intermittently?

[gustacus]

I own a 2016 ford focus 1L eco boost clocking in at around 56k miles. Looking after it best as I can knowing that the engines are prone to fail due to the wet belts.

The car has a stop start system in built which when bought was not working. I thought nothing off it possibly a battery that does not take it. However around a month ago done a long drive around 6 hour round trip of around 400 miles and coming towards the end of the journey the stop start system starts to work all off a sudden showing the green A symbol on the dash that it's engaged. The next day the system stops working again and has not since. I'm curious to what could be causing this to happen. I'm guessing it's a sign that the battery is past the point it can't support it but I'm not the most car savvy person on here some ideas/advice would be great!!

 

[HERTS P&D]

Don't worry about it. It kills starters and batteries.

Andy

 

[carmanmemoranda]

Battery issue.

Is it a stop start battery fitted?

 

[gustacus]

Battery issue.

Is it a stop start battery fitted?

I haven't actually checked but I imagine so If the battery is still stock and never been changed. But given how long it's been it's probably worth while for me getting a battery change soon. But not sure if it's worth the extra £150 or so for an agm battery.

 

[mattylad]

Is it actually £150 for one?
While they do cost more than an ordinary battery for a focus surely they are less than that?

 

[Mottie]

Battery. Sure sign when the start stop packs up.

The lady that used to work for me asked me to look at her daughter’s car - it was having the same problem. I went round to pick it up early one morning and she was in her dressing gown. She gave me the keys and I went to start it but it wouldn’t even turn over - battery was dead. I told her I’d need a push to get it started. She said “Let me just get dressed first" and went back inside. She came out about 30 seconds later, still in her dressing gown. "I thought you were going to get dressed" I said. "Nah, I just needed to put me knickers on in case I go arse over tit when pushing the car".

 

[carmanmemoranda]

Is it actually £150 for one?
While they do cost more than an ordinary battery for a focus surely they are less than that?

I'd expect that area for stop/start.

And yes get the right type. It has a smart charge system and needs the right type or you will get more issues.

 

[Brigadier]

Battery. Sure sign when the start stop packs up.

The lady that used to work for me asked me to look at her daughter’s car - it was having the same problem. I went round to pick it up early one morning and she was in her dressing gown. She gave me the keys and I went to start it but it wouldn’t even turn over - battery was dead. I told her I’d need a push to get it started. She said “Let me just get dressed first" and went back inside. She came out about 30 seconds later, still in her dressing gown. "I thought you were going to get dressed" I said. "Nah, I just needed to put me knickers on in case I go arse over tit when pushing the car".

Reminds me of a story, but it is off-thread so Mottie wouldn't approve

 

[Old Salt]

The stop/start systems I am familiar with rely on certain criteria being reached. Engine temperature, ambient temperature, air con settings etc. my merc has come on twice in 8k miles. Personally I hate the function and turn it off by default.

 

[Rodders53]

My 2019 Ford Galaxy has stop start.
It seldom works.
I don't do enough miles regularly enough.

It tells me it's shutting down to save battery charge most days I get in to use it.

In winter the Quickclear heated windscreen won't work due to the lack of battery voltage. Rear and mirrors work though! Ford tell me that's by design with the latest eco-saving vehicles.

I'll sometimes use a smart charger to pep up the battery and IF we then do enough miles on a run the Stop Start might decide to work. I think the last time it sprang into action was in a hilly area of Yorkshire where the regenerative braking (charging) pumped a lot into the battery. East Anglia just ain't hilly enough!

EDIT The battery gets the all clear on every service!
DO NOT replace an AGM stop start with a normal flooded wet lead acid. The charging system will need dealer alteration (if that's even possible) to match; and it'll get killed very rapidly without that.
AGM stop start will tolerate only being charged to 80% normally and have the capacity to absorb energy from regenerative braking. Wet LA's wont be happy with that depth of discharge regularly and the regen voltages will be too high, as well.

 

[pcaouolte]

On the Ford there is a smart battery charging system which is designed to only charge the battery to 80% of its capacity in normal use, this is to save fuel by reducing the alternator load on the engine. In some circumstances the alternator is enabled when the battery is at 80% or above, e.g. when going downhill the alternator is enabled to increase engine braking. So the battery charge will normally sit below 80% but will occasionally be above 80%. The stop start system needs the battery to be above 80% or it will not work. As stated above the system also needs engine temperature, ambient temperature and the cabin heating/cooling to be within specific ranges or stop start will not work.

Don't worry about it not working. It is designed to work for the duration of the emissions tests in order to show an artificially high mpg. In normal use it would just increase wear on the engine, starter and battery.

If you want it to work for a week then charge the battery to 100%. The smart charging system will spend the next week trying to get the charge level back down to 80% and then the stop start will fail again.

 

[Mottie]

In normal use it would just increase wear on the engine, starter and battery.

I’d be more concerned about the constant sudden loads on an aging cam belt.

 

[Rodders53]

Don't worry about it not working.

+1 on that!

If you want it to work for a week then charge the battery to 100%. The smart charging system will spend the next week trying to get the charge level back down to 80% and then the stop start will fail again.

If only it would take a week. Days, or less, I've found.

 

[pcaouolte]

I’d be more concerned about the constant sudden loads on an aging cam belt.

The cam belts are fine if the engines are serviced at the correct intervals, using the correct oil, and no-one puts engine flush chemicals in the engine. The other thing that kills them is having the car standing about unused for months with one end of the belt in the oil and the rest of the belt dry, this happened a lot during Covid.

 

[wv62]

I've got 2 vehicles with stop start. Luckily there's an app that you can use to turn it off on Minis and BMWs so I only have to remember to disable it each time I drive the Transit. I've never understood why anyone would want it on.