Technical Start-Stop not stopping

[Steph3071]

No start stop function even when the vehicle is up to temperature. Pull up to a traffic light, keep my foot on the brake, put in neutral and release the clutch.... nothing.
Stall the car and it will auto restart.
No message on the cluster to say start stop isn't available.
No faults in MES

Any suggestions?

 

[GrandePunto PL]

Use Fiat specific software (FES, MES, AlfaOBD) and check the ECU (ECM, UCM/MEC in French) and Body Computer modules, they are controlling/managing the Start&Stop function. Universal code readers are useless.

 

[Steph3071]

I've used MES both with and without the yellow adapter and no faults are stored in any of the modules on the car.
Given that it will auto restart if stalled I'm assuming the battery condition is goo. It was only replaced a couple of years ago as Start/Stop had stopped working completely and wouldn't even restart when stalled.

 

[Pugglt Auld Jock]

No start stop function even when the vehicle is up to temperature. Pull up to a traffic light, keep my foot on the brake, put in neutral and release the clutch.... nothing.
Stall the car and it will auto restart.
No message on the cluster to say start stop isn't available.
No faults in MES

Any suggestions?

So you pull up to a standstill and let the engine idle with the gearbox in neutral and foot off the clutch pedal, but the engine doesn't stop?
If you stall the engine and then select neutral with your foot off the clutch it restarts?

If so the first thing you need to monitor is live battery voltage. You need to know what the voltage is when you're expecting it to restart as the system will only initiate a stop if it perceives the battery to be sufficiently charged. However it will attempt to restart a stopped engine regardless. Ok the battery is new but many vehicles won't do stop start for the first few stops in a journey until the system has restored the voltage lost during the cold start. It takes my nearly new Skoda Scala about a couple of miles from a cold start before it will operate and if it's been left without starting for a week it can take quite a lot longer. (modern vehicles have permanently live systems which drain the batter even with the ignition off). You need to know what the voltage is and it would be useful to know what the voltage drops to when cranking the cold engine.

Although unlikely it's not impossible that the new battery may have a problem. Somewhere like Halfords will do a battery condition test which includes a cold cranking voltage test and definitively establish whether you have a battery problem or not. Once the battery is eliminated as a possible problem then you can confidently explore other possibilities. Mind you, the FIAT stop start performance is notoriously fickle. Many on here report problems with it not working or working only spasmodically. We had this with my son's Punto. It did improve with a new high quality Yuasa battery, but it still had a mind of it's own.

 

[Asteris]

Most likely the battery went bad. Not bad enough to not start the car, but bad enough for the BCM to detect it will be risky to stop the car at traffic lights. Happened twice on my brand new ClioV, six months from new the start-stop disengaged, dealer replaced battery, six months later same thing with the second battery and finally i installed myself an AGM aftermarket battery, that works fine for the last year.

The two faulty batteries would work fine for a day or two, when i charged them overnight with a battery charger. Try that if you have a charger.

 

[Pugglt Auld Jock]

Most likely the battery went bad. Not bad enough to not start the car, but bad enough for the BCM to detect it will be risky to stop the car at traffic lights. Happened twice on my brand new ClioV, six months from new the start-stop disengaged, dealer replaced battery, six months later same thing with the second battery and finally i installed myself an AGM aftermarket battery, that works fine for the last year.

The two faulty batteries would work fine for a day or two, when i charged them overnight with a battery charger. Try that if you have a charger.

If you're a cynical person you might believe it's all part of a dastardly plan to sell more batteries?

 

[Asteris]

Not far from the truth, but on the other hand, most modern batteries do not warn on the way out. One time my Seicento started fine in the morning, no slow crank or anything and 10 minutes later it died while cruising from battery failure. At least with the Punto I know i usually have 3 to 6 months to replace the battery when the Start-stop disengages. Prefer it this way, not fancy getting stranded now i'm getting older...