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Start Stop no longer working

5K views 39 replies 7 participants last post by  Sandyman 
#1 ·
I've had my 07 120D for a couple of years now and all is fine apart from the stop/start system which has gradually started to fail. When I first bought the car it was fine, it used to work intermittently, though after a good motorway run it would come back for a short while. Now even after long runs it won't work anymore. The battery was replaced at the beginning of 2018 and there have never been any electrical problems with the car, like not starting. Only one thing I noticed is that with the engine off it won't let me listen to the radio for that long before shutting it down after the battery symbol comes on...don't know if this is normal?
Anyway, is there a way to assess whether the battery just needs a good charge to get it working at max capacity again (I do tend to use the car in town mostly so no long journeys really)? Can someone recommend a decent charger if this is the problem?
Thanks
 
#2 ·
Did you register the battery to the car in 2018?

These cars have an intelligent battery monitoring system which charges older batteries more. So if you put a new battery in without registering it to the car, the IBS system still thinks it's the old battery and will overcharge it.

All those issues are signs of a duff battery. You can try charging it, but it may need a new one. I use a Ctek MXS 5 charger on ours.
 
#4 ·
Well I truly jinxed it with my post because I suddenly got a battery warning light while driving earlier! So...I think it was yellow so hopefully alternator OK. I didn't register the battery because I bought the car after it had been replaced, but it was probably not done simply because the garage was an Indy one and not specialist, but still you'd think any decent mechanic would know these things?!
I did check to see what battery was fitted and even took a pic in case I needed serial numbers etc...even though you can't see much info on the top. It's a Duracell Extreme 3X...not a lot of info about this model but I think it's an AGM one. So if it is just the battery it will have lasted just over 3 years- not great!
Now waiting for RAC- thankfully made it back home before starting problems.
Will update once I get a diagnosis.
 
#6 ·
Thanks Octavius yeah I'm thinking the same.
Anyway RAC man just took a look and found the drive belt was hanging loose in the engine bay! The tensioner pulley has sheared off and bearings sitting on the undertray. I'm glad I made it home!! Obviously battery wasn't getting charged by the alternator and water pump not doing its usual job so probably just prevented a complete disaster by being close to home. Belt looks ok so can reuse but gonna have to call my mobile mechanic...
Might as well charge the battery while waiting for mechanic to come out, some point next week now. Can I use a standard cheap car battery charger or does it need to be a Ctek jobby and the like?
 
#10 ·
#12 ·
Octavius said:
As long as it's good for AGM batteries any will do.

I would change the serpentine belt at the same time as the pulley assembly.
Which pulleys do you recommend I change? There's one just above the tensioner and one to the right at the bottom...I think they're both guide pulleys? I've seen they're both included in a kit so would that be the best option? Which are people finding have a good price/quality relationship?
 
#13 ·
Thanks guys...the charger looks good. I'm gonna wait until I get the pulleys and belt replaced as that's priority and anyway the battery might be okay. Managed to get the tensioner off plus one of the guide pulleys...not that hard just restricted in terms of space. Followed a video and took the front plastic airway, air filter housing and fan to create more room. Need to make sure the belt routing is right when it goes back on! There are plenty of pictures...
 
#14 ·
Well I feel pretty chuffed with myself really! Managed to get new tensioner and idler pulley on, then reused the belt. Did need a jump start but all was running sweet. Took it for a 15 mile drive and hey ho the stop start is now working again. Result! Hope it stays that way 😀. Cheers for all the help!
 
#16 ·
CoupeSilver said:
I'm a paranoid sod, and I would (did) get the Ctek CT5 stop start as it explicitly states on the specs that it doesn't go above 14.55 Volts, and AGM batteries should never be subjected to voltages above 14.7 as it damages them in the long term. So most chargers that have a desulphurisation phase should be avoided as that's the phase where they usually use high voltages (often over 15 Volts). Unless the specs say the maxium voltage the charger will output is below 14.7 Volts.
The MXS 5 charger actually has a button that says AGM and AFAIK it does the proper voltage. I've used it on all our BMWs to date with no issues and our E91 battery was only changed last year after 10 years service, with periodic charging with the Ctek. :)

As said above, it's also the one BMW sell as their official charger.

 
#18 ·
waldorf said:
Very good! Keep in mind that a deep discharge of the battery causes some permanent damage to it. So during a cold period it could struggle to get it cranked.
Yes well it probably has been damaged to some extent because the stop start is not working again. I'm sure it's because I only really use the car around town, but anyway I now need to consider whether I should charge it properly with the correct charger or get a new battery. What do you reckon?
 
#19 ·
Sandyman said:
waldorf said:
Very good! Keep in mind that a deep discharge of the battery causes some permanent damage to it. So during a cold period it could struggle to get it cranked.
Yes well it probably has been damaged to some extent because the stop start is not working again. I'm sure it's because I only really use the car around town, but anyway I now need to consider whether I should charge it properly with the correct charger or get a new battery. What do you reckon?
You could try giving it a good charge and see if that rectifies it - we did this on our E91 when the battery was starting to go and it probably kept it going for another 1-2 years before needing replacing.

Or just get a new battery. It was circa £175 on our E91 for a new Yuasa AGM battery, fitted and registered.
 
#20 ·
I decided to buy the Ctek charger and connected it up. It started off on the third led and so thought it might take a while, but kept on checking it every so often. I was a bit surprised when it reached full charge within about an hour though but obviously it wasn't that down on charge. Anyway I was quite confident that would do the trick and took it for a quick spin but sadly stop start still refusing to work 🙁. I can only conclude I need a new battery after all, if I want the stop/start (of course many aren't too bothered but I am!), or is there anything I'm missing that could be the culprit?
 
#21 ·
It can take a bit of time for it to start working. When we had our new battery it took a few days for start/stop to work, not sure why!
 
#23 ·
Your car is full with electronics and software, it is quite possible the car needs to see the battery for a longer time to do a kind of health check.
The ideal voltages are: 12.6 v with everything off. Engine running at 2000 rpm: 14.6 v. During cranking it should stay above 11 v.

Mine has the startstop off by default. I think it is better for your engine, so wouldn't bother too much.
 
#24 ·
Thanks waldorf I'll test the battery to see what voltages I get. Yeah as I said it doesn't bother many people but I suppose I like things to work properly on the car and as a DIY mechanic, want to learn and be able to fix things myself. Not only does it cut the exorbitant labour fees charged by many garages but I find it incredibly rewarding...of course thanks to forums like this and a community of like minded enthusiasts!
 
#25 ·
One other thing to remember - on the Exx cars, like yours and our e91, the stop/start system is very fussy and you have to meet many conditions for it to activate. It has to be over 10 degrees temp outside, you have to have driven more than 10ft, not have much steering lock on, battery in good condition and many others.

Our e91 stop/start wasn't working today, but then I noticed it was only 8 degrees outside.

The f22 system on my 240 is much easier to get working.
 
#26 ·
When is 8C it should. Condition that car check. Materials from BMW TIS.
-Vehicle stationary
-No gear engaged
-Clutch pedal not depressed
-Engine temperature not too low
-Ambient temperature above -3 °C
-Brake vacuum sufficient
-Battery's charge status is adequate
-Driver's seatbelt is engaged
-Vehicle has not just been operated in reverse

On vehicles with MSA the engine can also restart automatically without any action on the part of the driver. Irate customers and customer complaints based on this system characteristic are not signs that a malfunction is present! Samples of conditions under which a fully-automatic engine start is executed without driver action include:

-A/C request signal: For instance, in response to condensation on the windscreen.
-Low brake booster vacuum: Low brake vacuum can lead to safety risks during braking manoeuvres. The engine restarts to rectify this condition.
-Engine stalls.
-Severe battery discharge: A discharged battery can lead to a vehicle breakdown. The engine restarts to rectify this condition.
-Vehicle starts moving from a stationary starting point on an incline: When the vehicle (engine) is switched off numerous systems are deactivated. Without the support supplied by various vehicle systems a rolling vehicle constitutes a safety hazard. The engine restarts to rectify this condition.
 
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