Low battery voltage and battery light on

My battery light came on today and my battery voltage is consistently 12v even while car is running.

Why is this? How do I fix it? Alternator isn’t more than 3 years old and is the higher output one rather than the standard one. The battery is less than a year old and reads 12.2 when off

Your battery is going to be very unhappy ... it should be reading 12.6 when "off".
Charging voltage is about 14 v for a few minutes after starting, and then drops to about 13.6 or so.

Your alternator may have worn brushes, or a damaged regulator... The brushes are part of the regulator, so changing that out may "fix" it. It could have a blown coil or bad regulator diodes.

The instrument cluster is the source of the "battery monitor signal" (the small wire to the alternator), which in many systems is a field-powering circuit to kick the alternator into current generation at lower speeds than its own "self excitation" will produce.

The battery light is the instrument cluster's interpretation of the monitor signal. In Ye Olden Days, the idiot light was the voltage
difference between that monitor and the battery voltage. The Sprinter doesn't follow that model... it could well be complaining that the battery voltage is not responding to the attempt to get the alternator to make current.

--dick
p.s. it's always a good idea to test your *meter* against other known voltage sources (such as flashlight batteries) to verify its accuracy. (especially if you're like me and have a collection of free Harbor Freight voltmeters)
p.p.s. 2003 service manual: http://www.diysprinter.co.uk/reference/05 service manual.pdf

It’s a Bosch alternator bought brand new three years ago... I don’t see how it could of worn out. Is there a test procedure rather than buying a new alternator and replacing it?

A local battery shop will test/diagnose your alternator and your battery if they are a solid shop.

Ask who is good at your local auto parts store.
Be sure to check with Bosch, the alternator I bought recently has a lifetime warranty.

bill in tomahawk

Going off of what Bill wrote, most auto parts stores can test your charging system in situ. There’s also a possibility that your ground cables are starting to go bad, preventing proper charging. You should be able to figure it out pretty quickly with the parts shop’s testing equipment.

Good luck

Just because stranger things have happened...
Check all of the fuses under the steering column. There is also a heavy fuse for the alternator mounted on the battery post.

Some general fuse and relay information is here.

https://sprinter-source.com/forum/showthread.php?t=24683

vic

billintomahawk said:

Be sure to check with Bosch, the alternator I bought recently has a lifetime warranty.

bill in tomahawk

Click to expand...

"Lifetime" is defined by Bosch. "They" (actually only their dealers - in my case Europarts - SD) did not honor my claim with full documentation as it lasted longer (over 10-years) then "their" definition of "lifetime" (whatever that is - no number was provided). But I do agree that 3-years would likely fall within even their definition.

Well the light went off on its own today. Battery is reading 13.7 running and high 12s off. There was a lot of smoke coming from the engine that day the light came on as well? Also never figured that one out either. I’ll post if it turns back on and go to a battery place. Autozone and such has always seemed to lead me more astray than help but maybe there is an actual battery store with better equipment/operators

Well the light went off on its own today. Battery is reading 13.7 running and high 12s off. There was a lot of smoke coming from the engine that day the light came on as well? Also never figured that one out either. I’ll post if it turns back on and go to a battery place. Autozone and such has always seemed to lead me more astray than help but maybe there is an actual battery store with better equipment/operators

Did the smoke smell like burning vinyl/wire? Could have been one of the alternator wires...

You should have a good look see. Problems rarely autocorrect and where there is smoke.....