Random "Conv. functions disabled"
Thread Starter
Member
Joined: Feb 2013
Posts: 94
Likes: 3
From: Maryland
'05 SL55
Random "Conv. functions disabled"
I am having an issue where at random, the message will come up on the dash "convenience functions disabled".
I have a 1 year old battery, 1100 that checks out OK. Voltage is 13.9-14.1 and I've monitored on dash as well. It's still reading 13.9 when the message comes up. Goes away after awhile. Someone suggested battery control module. Any other ideas?
I have a 1 year old battery, 1100 that checks out OK. Voltage is 13.9-14.1 and I've monitored on dash as well. It's still reading 13.9 when the message comes up. Goes away after awhile. Someone suggested battery control module. Any other ideas?
Thread Starter
Member
Joined: Feb 2013
Posts: 94
Likes: 3
From: Maryland
'05 SL55
Several say that the aux battery has nothing to do with this error including my buddy who is a Mercedes Master Mechanic and owns the same car. That battery seems ok anyway, 12.8v
I guess I could take for a charging check but his shop is almost 2 hours away. Hoping to diagnose myself. If voltage isn't fluctuating. Why do you say it's a voltage problem?
I guess I could take for a charging check but his shop is almost 2 hours away. Hoping to diagnose myself. If voltage isn't fluctuating. Why do you say it's a voltage problem?
Super Member
Joined: Jun 2017
Posts: 899
Likes: 140
2005 E55
Several say that the aux battery has nothing to do with this error including my buddy who is a Mercedes Master Mechanic and owns the same car. That battery seems ok anyway, 12.8v
I guess I could take for a charging check but his shop is almost 2 hours away. Hoping to diagnose myself. If voltage isn't fluctuating. Why do you say it's a voltage problem?
I guess I could take for a charging check but his shop is almost 2 hours away. Hoping to diagnose myself. If voltage isn't fluctuating. Why do you say it's a voltage problem?
Also may potentially be the voltage regulator starting to fail. The computer is probably smart enough to recognize when a diode is starting to pass voltage that's not supposed to. If you have an o-scope you can take a look at your output and see if there is a ripple in it but still at good average voltage.
If battery voltages are good with the motor off(in the 12s) and voltages of the alternator are high enough with the car running, I would start with replacing the voltage regulator for <$20, then hope it's not the alternator taking a ****.
That's the path I took, but it ended up being the alternator. If it is, I got the duralast gold alternator (new, not reman) for $150 online and it's been working great so far.
Good luck.
Thread Starter
Member
Joined: Feb 2013
Posts: 94
Likes: 3
From: Maryland
'05 SL55
My alternator just went out recently. It initially established itself as the conv functions disabled message but only occasionally and went away shortly after. When ever i got torque opened and looked at voltage it was at like 14. Then over the course of a month it became more steady and I finally caught that voltage was dropping to 12ish randomly. Then it became consistent, and stopped charging the batteries all together.
Also may potentially be the voltage regulator starting to fail. The computer is probably smart enough to recognize when a diode is starting to pass voltage that's not supposed to. If you have an o-scope you can take a look at your output and see if there is a ripple in it but still at good average voltage.
If battery voltages are good with the motor off(in the 12s) and voltages of the alternator are high enough with the car running, I would start with replacing the voltage regulator for <$20, then hope it's not the alternator taking a ****.
That's the path I took, but it ended up being the alternator. If it is, I got the duralast gold alternator (new, not reman) for $150 online and it's been working great so far.
Good luck.
Also may potentially be the voltage regulator starting to fail. The computer is probably smart enough to recognize when a diode is starting to pass voltage that's not supposed to. If you have an o-scope you can take a look at your output and see if there is a ripple in it but still at good average voltage.
If battery voltages are good with the motor off(in the 12s) and voltages of the alternator are high enough with the car running, I would start with replacing the voltage regulator for <$20, then hope it's not the alternator taking a ****.
That's the path I took, but it ended up being the alternator. If it is, I got the duralast gold alternator (new, not reman) for $150 online and it's been working great so far.
Good luck.
I'll do a parts search on the voltage regulator and give that a shot first.
Thanks
MBWorld Fanatic!
Joined: May 2015
Posts: 4,037
Likes: 1,011
From: Miami, FL
2003 CL 600
Those ford alternators fail so often it's not even funny. I replaced so many of them when I used to work at Firestone, on trucks, cars, whatever. Easy to change but unbelievable failure rate.
To the OP, most of the advice so far is sound, to avoid throwing parts at it, i'd suggest dealer/competent MB independent diagnostics, but without that, regulator/alternator/battery module are you most likely steps.
To the OP, most of the advice so far is sound, to avoid throwing parts at it, i'd suggest dealer/competent MB independent diagnostics, but without that, regulator/alternator/battery module are you most likely steps.
