W211 E220 cdi 2004 Possible SBC issues

uk174

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Hi,
I have been getting a reduced braking...start engine message when I unlock the car in the morning.Took it to my local merc indie who put it on a star diagnostic and found no codes stored and said that the sbc was fine.
My question is if it is battery related then surely would I not have starting issues?
The only other problem that I am having is that sometimes when I lock the car the alarm goes off.
What should
the aux and main battery voltage readings be before I start the car and what voltage is deemed poor enough to warrant a battery change?
 

John

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The W211 is sensitive to even slightly lower voltages but the engine still starts and runs fine.

My previous W211 gave me jip on early 13s running (c13.2v) and late 12s off (c12.9v).

Once the alternator was replaced (batteries both done a couple of years before), I had no issues and was running in the 14.1v > 14.3v area.
 
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uk174

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Morning,
Forgot to add that I get different messages, not always the same. Sometimes get reduced braking, start engine, sometimes ..longer braking distance required , and also another along the same lines..
 

OneForTheRoad

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my main agm battery was old and only ever held a partial charge enough to start the car , i found out when i left the cd player on for a few hours that the battery was knackered as it went flat, but would still start the car normally . i got no braking errors at all . id recommend you check the dates on both batteries and charge both to see if errors go away , then take it from there .
 

John

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Saying all that, I only ever got spurious electrical gremlins and the usual convenience messages.

I'm not saying it is not this but the SBC-related issues you are getting too do sound a bit odd.

Would be worth testing your batteries and alternator function to rule that out.
 
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uk174

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Saga of SBC is still running ...have charged both batteries and yet still get a reduced braking-start engine warning when I unlock the car in the morning or at any other time for that matter.
Did an alternator test in that checked main battery voltage before starting car..12.7V and then after starting car..13.92. And then put lights,fan,radi and heated seats on to see voltage drop to 13.5 only to go back up to 13.92 once all applications were shut down.
Did the same test on the auxillary battery ...before starting 12.66...and after starting the same??
Is that how how it should behave..ie/no increase in voltage.
Getting a little fed up with this now as I dont really want to spend ££s on a new SBC despite the fact that my local indie told me there were no faults stored against SBC on his star diafnostic.
Could it have been an anomalie...is it worth getting the codes read again.
Finally, may I add that I only get this message on unlocking the car in the morning or if after the car has been left to stand for a while.
 

HB

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Get the codes read, it's the only way but, it sounds like your sbc is on the way out.
 
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uk174

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Oh dear..hoping that wasnt the case.Will have to go see indie again and see if any codes show up this time.
Thanks for taking the time to reply.
 

pmcgsmurf

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Why not get both batteries checked properly, you local Halfords or Kwik-Fit would do this for free?

I had similar problems on my old W211, checked the batteries and both were original (10+ years) so changed them both and problem went away.
 

OneForTheRoad

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whats the dates on your batteries ? esp the small one .
 
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uk174

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Cant seem to find date on the main one but the aux is 04/04...the original I guess. Have ordered a new one for Tuesday hopefully but in the meantime your right I will go and get the batteries tested.
thank you for the reply
 

OneForTheRoad

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aux will probs be goosed by now . hopefully a cheap fix for you .
 

John

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I'd get a second opinion from MSLP in Brum.

Acid knows his onions and will let you know what's actually going on...
 

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