g.matthews1987

Hi all,

Think i have an interesting one so any thoughts would be v much appreciated!

My 2015 C class W205 250d Bluetec has had an intermitent fault whereby it sometimes won't start. On the push of the button, the ignition lights come on but nothing happens. The engine doesn't crank at all. The engine light stays on, but disappears within a few seconds. Normally, a second attempt is required to start it and when it does, it runs fine. I sometimes have to push the button a couple of times which i understand cycles through ignition sequence and then the car starts fine.

I also have the same intermitent fault on the start/ stop. The light goes green, the engine stops, but doesn't always restart when i go to accelerate.

I've tried using my spare key and even putting the key into the ignition, but the problem persists. I had the main battery replaced 18months ago (Varta F21) and have charged it using a smart charger. Voltage once surface charge has dissipated is about 12.3v. On engine startup voltage drops to 8.5v-8.7v at a minimum. As soon as the engine has fired the voltage goes up to 14.5-14.6v.

I have checked the fuses and done a basic check on the relay on the starter and couldn't see any issue. I checked the resistance which was 82ohms which i have read is outside of tolerance on another forum so i have ordered a new relay just in case.

I do not have any fault codes using iCarsoft MB v2.0 with the latest firmware. Many people complain about the Aux battery (or capacitor) but i do not have a malfunction warning and the start/stop light goes green which makes me think the issue is on the starter circuit rather than the stop/start circuit.

Has anyone got any ideas what the problem could be before i have to take it into a stealership?

Many thanks

Cosworth2000

Hello, you have a major draw on your battery. Your battery should not drop to 8.5 when it starts up. It should remain around the 11-12v range. As you changed your battery, did you get the same amps or higher? This is not a problem with the aux battery there is something drawing on your battery. I would do a battery volt draw test.

g.matthews1987

Thanks. What sort of drain on the battery would be acceptable? Given the drop in voltage is instantaneous upon starting the engine do you think its likely to be on the starter circuit?

Cosworth2000

Check to see your battery and also to see what is drawing. You need our cars to go to sleep but you need the hood to be up. So open the hood, then leave the car (locked or Unlock) for 15-20 minutes. Then go under the hood and check the battery. For Mercedes it should not be more than 0.1- 0.2 amp drawn. Any more than this could draw the battery amps down.

stockbmw

Have your battery tested and claim the warranty for a new battery. Since your car is out of warranty and having start/stop problems, I would disable the feature upon entering the car either put on individual mode or press the buttton. You can manually press the button to stop the engine when waiting at the lights.

What's next, the starter failure?

g.matthews1987

Ok, I've had the battery tested at the battery is fine and in full working order. It was put on a proper battery tester rather than just taking the voltage. I understand I can turn off the eco stop start, but the biggest problem is that the car doesnt always start (can be hot or cold). I am mainly worried about my wife being out with the kids and the car not starting at all.

I read somewhere there is a relay or solenoid as part of the stop/start by the wiper motor, anyone got any ideas about this?

I've noticed that when it fails to start there is a click coming from the engine (assuming this is the starter engaging) but nothing happens. I can only just see the starter motor but cant get to it. The ignition lights go off and the engine light remains on but goes off after a little while. I've tried to see if anything is apparent on my iCarsoft MB v2 tool but cant see anything.

Any other ideas would be greatly appreciated, but just to be clear the issue occurs upon starting the car from the ignition and upon restarting from an eco stop/start. Thanks

stockbmw

Your battery reading of 8v is not right when you start the car. Should not dip below 12v else problem like yours occurs where starter don't get enough juice to start the car.

Go get your battery tested by another store like AutoZone for free, you should get a print out saying your battery is defective, use this to get new battery since this one is still under warranty.

And how many days is your car being driven in a week?

g.matthews1987

The car is driven every day but journeys are short so i charge the battery every now and then. I'll get it checked and come back.

With the drop in voltage on starting, could this stop the car from cranking period? Not sure how much drop in voltage there is when the car fails to start given the starter isn't drawing. The bit thats odd to me is the fact that normally on the second attempt the car starts straight away, no hesitation.

stockbmw

Your 12v starter needs 12v to crank. Anything under it won't give necessary speed to start the motor. Don't ask about why 2nd attempt work or not because 1st don't work and you are worry about your wife being stuck in boonies. You saw 8v when starting and that's dead give away resistance under load fail to start because of faulty battery.

Easiest solution is go buy 12v battery with good return policy like Costco and use it for a week to rule out the battery. Be sure to test this while cranking to see if it drops to 8v or hovers at 12v.

g.matthews1987

Ok, i have had the battery fully tested and its passed all of their checks including status of charge, battery life, cranking health and also had the alternator tested which was fine.

Any other suggestions?

MBenzOwner

I have this issue. The dealer and many from the forum couldn’t solve. The dealer spent hours of diagnostic labor without figuring it out. There are reports on NHSTA and scattered reports on the forums. See the below posts for all the things already looked at. It’s a pretty exhaustive list.

https://mbworld.org/forums/c-class-w...-stalling.html

It isn’t a simple battery issue. New battery and auxiliary battery / voltage converter didn’t fix it.
Also you need xentry to get the all the codes since those code readers don’t pick up everything. I have P1CE200 which is basically Eco start / stop detected low engine speed

realeric

Scan the car with xentry. iCarsoft is a good tool but there could be hidden record.

I have seen 10.7~10.8V when cranking, but 8.x is not normal even if the battery passed the test. Or the start motor drains power abnormally. Check the start motor relay…. if you couldn’t find the cause.

kashief682

Hey, how did you eventually fix this issue