Overcharging - m931a2

[roders]

Guys can anyone assist please,

I Have an AMG M931A2. Had problems with Alternator over charging and putting ABS light on !!! replaced with new Alternator, ran for 30minutes, all ok, ABS light out ,checked Alternator output reading 27Volts.

Voltage gage showing in green perfect then suddenly volt gage shoots into the red and ABS lightcomes back on. Leave for 2hrs, try again, run for 30 mins then problem reoccurs!

Thought it could be the Control Box - replaced this everything ok or so I thought - ran further 15 minutes and everything started over again. Over Charging Volt Gage in red, batteries starting to boil! Not good.

I have changed the 4 x themal fuses also, checked all earths, cannot think of anything more that could cause this problem.

Question - any one out there had same problem and if so what was the cause of this overcharging down to ?

Look forward to hearing from someone who has experienced this problem before.

 

[porkysplace]

I would lean towards a bad voltage regulator.

 

[PureMayhem]

I can't read a word you wrote in that blue font unless I highlight it. I am just saying.

 

[hklvette]

I would lean towards a bad voltage regulator.

Agreed. Once the regulator gets hot, something in it is failing. A common symptom in electronics that are on their way out.

 

[roders]

Thanks for the reply. Have tried 3 voltage regulator boxes. still the same problem. Tried 2 Alternators. Changed 4 thermal fuses, disconnected CTIS and ABS. Still problems after 30 mins running after cold???

 

[73m819]

You have a NON circuit breaker controlled circuit short somewhere that ONLY happens when the engine is running, good luck on finding it, this kind of short will trick the alt. into thinking the batteries are down and then you get the overcharging.

 

[Julian]

I have noticed a similar problem with my 923, except if it is going to do it, it will do it at start-up. Voltage goes into the red, ASB light on. I have discovered that turning off the master switch and back on clears the problem. Also sometimes when I turn on the master switch, the gages do not come on unless I recycle the switch. I think you should also look for an open circuit or an intermittent relay. I suspect a relay or loose connection in mine but have not had time to trouble shoot.

 

[roders]

Hi many thanks for your help ,I even have STE/ICE Tester and could not find anything wrong running full test on starter/Alternator and Batteries found nothing ! my next try will be fit 4 x new Batteries and recheck all connections and earths on the truck then run another test (NG50) with the STE/ICE and see what we get ,unfortunately can do this till this weekend but will shoot you a email to let you know how things turn out,
Cheers Roders.

 

[stampy]

Mine does this on start up for about 3-4 min . I assume this is due to the low battery issue but I am concerned that it may be harder on the batteries due to there only being two. While I know 4 is preferable due to capacity two batteries start and run the truck just fine here in NC. Any easy work around so its not overcharging the batteries for 3-4 min or will this not hurt them?