W221 S350 Bluetec No lights on dash

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S350L

Active Member
Joined
Jan 1, 2016
Messages
72
Car
Mercedes
Hi Guys

ive a 2011 S350L Bluetec which is currently being a pain with an intermittent fault, which isn’t throwing up any codes.

Sometimes it starts 1st time and sometimes it doesn’t. Put the key in and there’s no lights on the dash. Turn the key, no response. Wait for up to 10 mins then it will work. It does seem to be getting worse.

ive put a new battery on her as the old one was reading 10.5 volts and have replaced the batteries in both keys


Any ideas please or anyone else had the same



many thanks in advance
 
Have you checked / changed the auxilliary battery in the boot?
 
i had similar fault with no codes on c320 i know its a differant set up but i found after removing sam unit it had water ingress some pins on plugs and relays where green so a good clean did the trick i used a contact cleaner and then sprayed it with wd40 while i was there i did the other sam in the boot. good luck
 
Thank you, any idea what type of battery it is

I have a 2011 S350 bluetec with standard wheelbase. The aux. battery on mine is a 12V AH, MB ref: A0009829308.

I would imagine that yours is the same, but I would strongly advise to check it out before ordering.
 
On my SL the car will tell you if the auxiliary battery is low and temporarily disable some non critical functions. The car should still start if the starter battery is ok, at least mine did.
 
i had similar fault with no codes on c320 i know its a differant set up but i found after removing sam unit it had water ingress some pins on plugs and relays where green so a good clean did the trick i used a contact cleaner and then sprayed it with wd40 while i was there i did the other sam in the boot. good luck

i forgot to add my fan was running realy fast when fault was happening on mine
 
Quote ive put a new battery on her as the old one was reading 10.5 volts and have replaced the batteries in both keys Quote

If it was reading 10.5 volts it wouldn`t even try to start the car.

You could try disconnecting the small sensor attached to the negative clamp of the starter battery, fully charge the starter battery or take car on long run then see what happens, if no change reconnect the sensor. To check battery voltage correctly charge battery, release bonnet, park car over night, do not open any doors, next day lift bonnet, uncover battery, test across battery terminals with multimeter, should read 12.8 volts. The Aux battery is for stop/start only, nothing else, if certain systems are closed down that`s due to the engine management unit reading the state of charge of the starter battery from the sensor attached to the neg clamp, it does that to ensure the starter battery has enough energy to restart the car after the stop/start system has stopped it.

I have a C-Class coupe Dec 2011 with both original battery`s , starter battery shows 12.8 volts, Aux shows 12.7, sensor was disconnected over 1 year ago.

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What about a pwer relay and where are they located
 
It’s not the rear battery, it reads 13.4volts
 
SOLVED. It was the EIS
 

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